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THE ALKALOIDS Chemistry and Pharmacology VOLUME 44

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THE ALKALOIDS Chemistry and Pharmacology Edited by Geoffrey A. Cordell College ofP/itir ni~ii:v University qf Illinois (11 Chicogo C/2iCYZ~O. IIlinois

VOLUME 44

Academic Press, Inc. A Division o j Horcoiirt Brrrce & Cotnpntz>’

San Diego New York Boston London Sydney Tokyo Toronto

This book is printed on acid-free paper. @ Copyright 0 1993 by ACADEMIC PRESS, INC. All Rights Reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publisher.

Academic Press, Inc. 525 B Street, Suite 1900, San Diego, California 92101-4495 United Kingdom Edition published by ACADEMIC PRESS LIMITED 24-28 Oval Road, London NW 1 7DX

International Standard Serial Number: 0099-9598 International Standard Book Number:

0-12-469544-2

PRINTED IN THE UNITED STATES OF AMERICA 9 3 9 4 9 5 9 6 9 7

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CONTENTS

............................................ ............................................

CONTRIBUTORS ...... PREFACE. . . . . . . . . . . .

vii ix

Chapter I . The Tropane Alkaloids A N D TAIUATAMMINEN MAURILOUNASMAA

I. Introduction .............................. 11. Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I l l . Synthesis ...................................... IV. Reactions

................... ..............................................

I 3 78 89 92 95 97 99 I00

Chapter 2. The Biosynthesis of Tropane Alkaloids

J. ROBINSA N D NICHOLAS J. WALTON RICHARD Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Organ Tissue Cultures for Biosynthetic Studies ............... Formation of Putrescine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . FormationofTropinone ......................... . . . . . . . . . . . . . . . . . . . Formation of Tropine and Pseudotropine . Formation of Acidic Moieties of Tropeines ........................... Formation of Tropeines ........................... Metabolism of Tropeines ......................... Degradation and Oxidation of Tropeines ............................. X. Overall Regulation of Pathway ....................... XI. Future Prospects ................................ References .......................................................

I. 11. 111. IV. V. VI. VII. VIII. IX.

I16 I19 I30 134 146 151 155

160 164 168 I80 I82

Chapter 3. Simple Indolizidine Alkaloids A N D TAKEFUMI MOMOSE HIROKITAKAHATA

I. Introduction ...................................................... 11. Indoiizidines with Alkyl and Functionalized Alkyl Appendages

III. Elaeocarpus Alkaloids

.........

.............. ._............................. V

189 190 22 I

vi

CONTENTS

IV . Slaframine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . V . Hydroxylated lndolizidines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VI . Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References .......................................................

223

228 250 250

Chapter 4 . Chemistry and Biology of Carbazole Alkaloids

D . P . CHAKRABORTY I . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I1 . Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111. Chemistry of Carbazole A loids ................................... IV . Physical Properties of Carbazole Alkaloids ........................... .... V . Biogenesis of Carbazole Alkaloids ................... VI . Biochemical and Medicinal Properties of Carbazole AIka Related Compounds . . . . . . . ....................... References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....

CUMULATIVE INDEX OF TITLES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

258 258 258 349

351 352

360

365 373

CONTRIBUTORS

Numbers in parentheses indicate the pages on which the authors’ contributions begin

D. P. CHAKRABORTY (257), Institute of Natural Products, Calcutta 700 036, India MAURILOUNASMAA (l), Laboratory for Organic and Bioorganic Chemistry, Technical University of Helsinki, SF-02150 Espoo, Finland TAKEFUMI MOMOSE(189), Faculty of Pharmaceutical Sciences, Toyama Medical and Pharmaceutical University, Toyama 930-01, Japan RICHARDJ. ROBINS( 1 15), Agricultural and Food Research Council Institute of Food Research, Norwich Laboratory, Colney, Norwich NR4 7UA, United Kingdom (189), Faculty of Pharmaceutical Sciences, Toyama HIROKITAKAHATA Medical and Pharmaceutical University, Toyama 930-01, Japan TAIUATAMMINEN (l), Laboratory for Organic and Bioorganic Chemistry, Technical University of Helsinki, SF-02 150 Espoo, Finland NICHOLAS J. WALTON(1 IS), Agricultural and Food Research Council Institute of Food Research, Norwich Laboratory, Colney, Norwich NR4 7UA, United Kingdom

vii


PREFACE

The scientific accomplishments of Professor Edward Leete, who contributed so much to alkaloid chemistry and biochemistry during his brilliant and illustrious scientific career, are honored in this volume by two chapters on the tropane alkaloids, an area of alkaloid research that was especially dear to him. The format for the presentation of these two chapters is new to this series. In Chapter I , Lounasmaa and Tamminen provide a complete summary of the occurrence of the more than 200 tropane alkaloids characterized and also review the synthetic pathways that have been developed for their formation. In Chapter 2, Robins and Walton describe the tremendous progress that has been made in the level of understanding of the intricate tropane alkaloid biosynthetic pathway. As is now revealed, seminally by Leete and co-workers, the biosynthesis of the tropane alkaloids, particularly the most infamous alkaloid, cocaine, is substantially more complex than originally envisaged. As details of these processes and the enzymes involved are further studied and characterized, the intense subtlety of the pathways is becoming apparent. Takahata and Momose review the simple indolizidine alkaloids in Chapter 3. These alkaloids are widely distributed in nature and some, such as castanospermine (a potent glucosidase inhibitor), have been the subject of intense synthetic and biological interest in the recent past. Finally, in Chapter 4, the isolation, synthesis, and biological responses of the carbazole alkaloids is reviewed by Chakraborty. Ranging from the simple analogs present in Murraya species to the complex derivatives found in certain fungi, the group displays a broad spectrum of structural diversity and biological activity. Geoffrey A. Cordell University of Illinois at Chicago


-CHAPTER 1-

THE TROPANE ALKALOIDS MAURILOUNASMAA A N D TARJA TAMM~NEN Laboratory f o r Organic and Bioorgunic Chemistry Technical University of Helsinki SF-02150 Espoo, Finland

I . Introduction ........................ 11. Occurrence

.................................... .....................................................................

...................................

.80

....................82

E. Lansbury Synthesis ......................

K. Jung et al. Syn L. He and Brossi

I

gongteng A ..............................

............................................. .89 ...................89

IV. Reactions .......

C. Photocyanation ..

.............................................................. .91 References .....................................................................

I. Introduction The tropane alkaloids have been reviewed on six earlier occasions in this series (1-6). Although a relatively short time has passed since the 1 THE ALKALOIDS. VOL 44 Copyright CJ 1991 by Academic Pre,,. Inc All right\ of reproduction in m y form raerved

2

MAURl LOUNASMAA A N D TARJA TAMMINEN

last review (6) in 1988, the number of known structures has increased dramatically, from 151 to 200 (i.e., 203 - 3; vide infra). To bring the record up to date, a new chapter has been prepared, following the same general lines as before (6). The focus is on areas where major changes have taken place (especially in the areas of occurrence and synthesis). Sections addressing areas in which there has been little activity are quite short (e.g., the section on spectroscopy). In the following chapter, Robins and Walton (7) review biosynthesis of the tropane alkaloids; thus, our section on biosynthesis is short, despite the significant changes that have occurred in this area. The literature is covered up to June 1992. In addition, some recent articles, appearing since the completion of the original manuscript, have been added to the reference list. The tropane alkaloids are a structurally well-defined group of natural products, and the mydriatic and anesthetic properties of several of the tropane alkaloids were exploited long before the structures were elucidated (8).Although an extensive literature exists on the pharmacological properties of tropane alkaloids, these are touched on only briefly. Readers with a deeper interest in the subject are referred to other publications (9-12) and to the references given in Section VII. The common structural element of the tropane alkaloids is the azabicyclo[3.2. lloctane skeleton, and the systematic name for tropane is 8-methyl-8-azabicyclo[3.2. ]]octane (Fig. 1). Applying the uniform numbering system presented in Fig. I , most disubstituted tropane alkaloids designated as C-3, C-6 disubstituted in the literature become C-3, C-7 disubstituted. The same principle, where applicable, is applied to the C3, C-6, C-7 trisubstituted tropane alkaloids. The C-3, C-7 notation is also used where the choice between the C-3, C-6 and C-3, C-7 notation in the literature has been arbitrary. Only in cases where the determination of absolute configuration has a solid basis, and where the structure is correctly presented by the C-3, C-6 notation also in the present numbering system, has the original C-3, C-6 notation been retained. The strict applica-

Me 7

6

5

\

4

6 FIG. 1. Ring system of the tropane alkaloids.

1.

TROPANE ALKALOIDS

3

tion of the system adopted here is certainly in several cases a simplification of the real situation and should be regarded as such. Because the systematic names in the tropane series are often long and used by very few authors, the traditional nomenclature is followed here. Trivial names are used where they exist, while for other compounds a semisystematic name based on the word “tropane” (vide infra) is adopted. In Tables II-IV, however, the nomenclature is based entirely on the semisystematic names (except for dimers and the trimer), and the trivial names are given in parentheses.

11. Occurrence The tropane alkaloids mainly occur in the plant family Solanaceae, but are found as well in the families Convolvulaceae, Erythroxylaceae, Proteaceae, and Rhizophoraceae (Tables I and 11). In addition, the presence of tropane alkaloids has occasionally been indicated in the families Brassicaceae (=Cruciferae), Euphorbiaceae, and Olacaceae (see Tables I, 111, and IV) (13-15). During the preparation of our earlier review (6), we became acutely aware of the lack of reliable information on the natural occurrence of tropane alkaloids. As a means of correcting this situation, we have collected in this chapter as much information as possible on the distribution of tropane alkaloids in plants. Thus, our main effort during the preparation of the present review was focused on the occurrence of the tropane alkaloids. The results are brought together in Tables 111 and IV. The earlier claimed natural occurrence of compounds 113, 144, and 185 (vide infra) has turned out to be erroneous. To preserve the created numbering system intact, however, and to indicate the proposed structures, compounds 113,144, and 185 are nevertheless included in Table I1 (with footnote explanations); the compounds are omitted from Tables 111 and IV. No chemotaxonomic conclusions should be drawn on the grounds of this review alone, without resort to the original papers. The plant organs from which the alkaloids have been isolated are indexed in some detail, but information concerning the geographical distribution and seasonal changes in occurrence are omitted, as well as the relative proportions of the various alkaloids. Reference to the original papers is therefore still necessary. In spite of these limitations, we believe that this compendium,

TABLE I BOTANICAL CLASSIFICATION OF PLANTS CONTAINING TROPANE ALKALOIDS Dicot yledoneae Malviflorae Euphorbiales Euphorbiaceae Phyllanthus Violiflorae Tamaricales Brassicaceae ( = Cruciferae) Cochlearia Proteiflorae Proteales Proteaceae Agaslachus Bellrndena Darlingia Knightia M yrtiflorae Rhizophorales Rhizophoraceae Bruguiera Crossostylis Pellacalyx Rutiflorae Geraniales Erythrox ylaceae Erythroxylum Sect. I1 Macrocalyx Sect. I11 Rhabdoph yllum Sect. IV Leptogramme Sect. V Heterogyne Sect. VI Archerythrox ylum Sect. IX Microphyllum Sect. X Melanocladus Sect. XI Sethia Sect. XI1 Lagynocarpus Sect. XIV Coelocarpus Sect. XVI Venelia Sect. XVIl Pachylobus Santaliflorae Geraniales Olacaceae Hcisteria

TABLE I (continued) Solaniflorae Solanales Solanaceae Anthocercoideae Anthocercideae Anthocercis Anthotroche Crenidium Cyphanthera Duboisia Grammosolen Symonanthus Cestroideae Salpiglossideae Schizanthus Solanoideae Solanineae Solaneae Cyphomandra Ph ysalinae Physalis Withania Jabroseae Latua Salpichroa Datureae Datura Sect. Brugrnansia Sect. Dutra Sect. Ceratocaulis Sect. Datura Solandreae Solandra Nicandreae Nicandra Atropoideae Atropeae Atropa Hyoscyamus Mandragora Physochlaina Przewalskia Scopolia" Convolvulaceae Calystegia Colutea Conuoluulus Erycibe Euoluulus a

Including species of Arropanthe and Anisodus.

5

6


covering all known plants with tropane alkaloids, will be a valuable source of information. Reference to original articles rather than reviews has been preferred. Our original intention was to cover the literature of the nineteenth century as well. However, it became evident that referring to those papers would only have caused confusion, as in many cases both the botanical and chemical identifications were doubtful. Overviews of the older literature are included in relatively recent papers on Duboisia (16,17),Datura Sect. Brugmansia (18), Atropa (19), Withania (20), Mandragora (21,22) and Erythroxylum (23).

1 . Botanical Classification The system of Dahlgren (24,25) was used for the general botanical classification (Table I). The family Solanaceae, the principal source of tropane alkaloids, has been classified according to the chemotaxonomic system of TCtCnyi (26), but incorporating the revision of the subfamily Anthocercideae by Haegi (27). Families containing only a few “tropane genera” have not been subdivided. The main principle in listing the genera and species in Table 111 was to employ one name for one taxon. A more ambitious botanical treatment was found to be impossible. Even this seemingly trivial goal was difficult to achieve in cases where the literature covered a long time period-more than 100 years for some species of the Solanaceae. A uniform scheme was also difficult to formulate when results pertaining to the same genus flourishing in different parts of the world had to be summarized. The names used in the original papers are mentioned wherever they differ from the ones employed in this text. The nomenclature was adopted from botanical monographs when available. Fortunately Datura, perhaps the most complex genus, has been the subject of a thorough analysis by Hammer et al. (28). The section Brugmansia, not included in that monograph, has been treated according to Bristol (29,30). It was impossible to treat the species D . arborea L. and D . candida (Pers.) Saff. separately, although Bristol presents them as distinct species, as an indication of the species investigated was lacking or misleading in several cases. It is very probable that the name D . arborea has been widely used in the chemical literature as a synonym for D . candida (31). The genus Atropa has been arranged according to Heltmann (32). This approach was adopted because it covers the whole genus, even though it may not be a botanically valid revision. Scopolia is mainly treated in the manner of Weinert ( 3 3 , but even in this case some questionable species outside Weinert’s treatment (S. anomala and S . paruijloru) were included in the list.

7

1. TROPANE ALKALOIDS TABLE I1 TROPANE ALKALOID STRUCTURES Alkaloid

Structure

1. 3a -Monosubstitutedtropanes The 3a-monosubstituted tropanes consist of 49 representatives. All members (1-49)are formally derived from 3a-hydroxytropane (1)or from the not yet naturally found 3ahydroxynortropane.

3a-Hydroxytropane ( = tropine) 3a-Acetoxynortropane 3a-Acetox ytropane 3a-Propiony lox ytropane

3a-(Hydroxyacetoxy) tropane 3a-Tigloylox ynortropane

3a-Butyryloxytropane 3a-Isobutyryloxytropane ( = butropine) 3a-Isovalerylox ynortropane ( = poroidine) 10 3a-(2’-Methylbutyryloxy)nortropane ( = isoporoidine) 11 3a-Tigloylox ytropane

12 3a-Senecioylox ytropane

13 ( + )-3a-(Z’-Methylbutyryloxy)tropane ( = valtropine) 14 3a-Isovalerylox ytropane 15 3a-Benzoyloxynortropane 16 3a-(Z’-Furoyloxy)tropane 17 3a-Tigloyloxytropane N-oxide 18 3a-Benzoyloxytropane 19 3a-Phenylacetoxynortropane 20 3a-Apotropoyloxynortropane ( = aponoratropine) 21 3a-Cinnamoyloxynortropane 22 3a-Phenylacetoxytropane 23 3a-(3’-Hydroxybenzoyloxy)tropane ( = cochlearine) 24 3a-Apotropoyloxytropane ( = apoatropine) 25 3a-Cinnamoyloxytropane

R = Me, R, = H R = H, R, = acetyl R = Me, R, = acetyl R = Me, R, = propionyl R = Me, R, = hydroxyacetyl R = H, R , = tigloyl R = Me, R, = butyryl R = Me, R, = isobutyryl R = H, R, = isovaleryl R

=

H, R,

=

2-methylbutyryl

R = Me, R, = tigloyl R = Me, R, = senecioyl R = Me, R, = 2-methylbutyryl R = Me, R , = isovaleryl R = H, R, = benzoyl R = Me, R , = furoyl R = Me, 0, R, = tigloyl R = Me, R , = benzoyl R = H, R, = phenylacetyl R = H, R, = apotropoyl R = H, R, = cinnamoyl R = Me, R, = phenylacetyl R = Me, R, = 3-hydroxybenzoyl R

=

Me, R ,

R

=

Me, R, = cinnamoyl

=

apotropoyl

(continued)

8

MAURI LOUNASMAA A N D T A N A TAMMINEN

TABLE I1 (continued) Alkaloid 26 ( -)-3a-(1’,2’-Dithiolane-3’27

28 29

30 31 32 33 34 35

36 37

38 39

40

carbony1oxy)tropane ( = brugine) ( ~)-3a-Tropoyloxynortropane ( = noratropine) ( - )-3a-Tropoyloxynortropane ( = norhyoscyamine) 3a-(4‘-Methoxybenzoyloxy)tropane ( = datumetine) 3a-(3’-Hydroxyphenylacetoxy)tropane 3a-(4’-Hydroxyphenylacetoxy)tropane 3a-Vanilloyloxynortropane ( = convolidine) (?)-3a-Tropoyloxytropane (=atropine) ( - )-3a-Tropoyloxytropane ( = hyoscyamine) ( -)-3a-(2’-Hydroxy-3’phenylpropiony1oxy)tropane ( = littorine) 3a-Vanilloyloxytropane ( = phyllalbine) 3a-Veratroyloxynortropane ( = convolvine) 3a-Tropoyloxytropane N-oxide I ( = hyoscyamine N-oxide 1) 3a-Tropoyloxytropane N-oxide 2 ( = hvoscvamine N-oxide 2) . 3a-Veratroyloxytropane( = convolamine)

41 3a-Veratroylox y-N-hydroxynortropane

Structure

1,2-dithiolane-3-carbonyl

R

=

Me, R,

R

=

H, R ,

=

tropoyl

R

=

H, R,

=

tropoyl

R

=

Me, R,

=

4-methoxybenzoyl

=

R = Me, R, = 3-hydroxyphenylacetyl R = Me, R, = 4-hydroxyphenylacetyl R = H, R, = vanilloyl

R = Me, R, R = Me, R,

tropoyl tropoyl

= =

R = Me, R, = 2-hydroxy-3phen ylpropion yl R = Me, R, = vanilloyl R = H, R, = veratroyl R

=

Me, 0, R ,

R

=

Me, 0, R, = tropoyl

R = Me, R , R = OH, R,

= =

=

tropoyl

veratroyl veratroyl

( = convoline)

42 3a-Feruloyloxytropane 43 3a-Veratroyloxy-N-formylnortropane ( = confoline)

44 3a-Veratroyloxytropane N-oxide

R R

= =

Me, R , = feruloyl CHO, R , = veratroyl

R = Me, 0, R, = veratroyl

( = convolamine N-oxide)

45 30-(3’,4‘,5’-

46 47 48 49

Trirnethoxybenzoy1oxy)nortropane ( c )-3a-Veratroyloxy-Nisopropylnortropane ( = convosine) (?)-3a-Veratroyloxy-Nacetylnortropane ( = convolicine) 3a-(3’,4’,5’-Trimethoxy benzoy1oxy)tropane 3a-(3’,4‘,5‘-Trimethoxy cinnamoy1oxy)tropane

R

=

H, R,

=

3,4,5-trimethoxybenzoyl

R = i-Pr, R, = veratroyl R

=

acetyl, R, = veratroyl

R

=

Me, R,

R

= Me, R, = 3,4,5trimethox ycinnamoyl

=

3,4,5-trimethoxybenzoyl

I.

9

TROPANE ALKALOIDS

TABLE I1 (continued) Alkaloid

Structure

2. 3p-Monosubstitutedtropanes The 3P-monosubstituted tropanes comprise 3p-hydroxytropane (SO), its five naturally occurring ester derivatives (51,52,53, 55, and 56), and the nortropane derivative 3Pbenzoyloxynortropane (54).

50 51 52 53 54 55 56

3P-Hydroxytropane 3P-Acetoxytropane 3P-Tigloyloxytropane ( = tigloidine)

3P-(2’-Methylbutyryloxy)tropane 3P-Benzoyloxynortropane 3P-Benzoyloxytropane ( = tropacocaine) 3P-Cinnamoyloxytropane

R = Me, R, = H R = Me, R, = acetyl R = Me, R , = tigloyl R = Me, R, = 2-methylbutyryl R = H , R, = benzoyl R = Me, R, = benzoyl R = Me, R, = cinnamoyl

3. 3n,6/3- and 3a,7fi-disubstitutedtropanes The base compound of the large group of disubstituted tropanes (63 representatives) is 3a,7P-dihydroxytropane (57). All other compounds (58-119) are mono- or diesters of 57 or of the corresponding 3a,6P-derivative.

R

57 3a,7P-Dihydroxytropane 58 3a-Acetoxy-7P-hydroxynortropane 59 ( + )-3a-Acetoxy-7P-hydroxytropane 60 3a-Hydroxy-7P-acetoxytropane 61 3a-Hydroxy-7P-propionyloxytropane

R = Me, R, = Rz = H R = H, R , = acetyl, Rz = H R = Me, R, = acetyl, Rz = H R = Me, R , = H. Rz = acetyl R = Me, R, = H, R2 = propionyl

(continued )

10

MAURl LOUNASMAA A N D TARlA TAMMINEN

TABLE I1 (continued) Alkaloid 62 (

+ )-3a-Hydroxy-7P-

Structure

R = H, R,

=

H, R2

=

tigloyl

tigloyloxynortropane 63 64 65 66 67 68 69 70

3a-Tigloylox y-7P-h ydrox ynortropane

3a-Isobutyryloxy-7~-hydroxytropane 3a-H ydrox y -7P-isobutyrylox ytropane

3a-Hydroxy-7~-tigloyloxytropane 3a-Hydroxy-7~-angeloyloxytropane 3a-Tigloyloxy-7~-hydroxytropane 3a-Senecioyloxy-7~-hydroxytropane ( - )-3a-Hydroxy-7P-(Z'methylbutyry1oxy)tropane 3a-Isovaleryloxy-6~-hydroxytropane 3a,7P-Diacetoxytropane 3a-Benzoyloxy-7f3-hydroxynortropane 3a-Hydroxy-7~-benzoyloxytropane 3a-Benzoyloxy-7~-hydroxytropane

71 72 73 74 75 76 3a-Phen ylacetox y-7P77 78 79 80 81 82 83 84 85 86 87

88 89 90 91

R R R R R R R R

= = = = = = = =

H, R, = tigloyl, R2 = H Me, R, = isobutyryl, R2 = H Me, R, = H, R2 = isobutyryl Me, R, = H , R2 = tigloyl Me, R, = H , R2 = angeloyl Me, R, = tigloyl, R2 = H Me, R, = senecioyl, R2 = H Me, R, = H, R2 = 2-methylbutyryl

R R R R R R

= = = = = =

Me, R, = isovaleryl, R2 = H Me, R, = R, = acetyl H, R, = benzoyl, R2 = H Me, R, = R2 = H, benzoyl Me, R, = benzoyl, R2 = H H, R, = phenylacetyl, R2 = H

hydrox ynortropane 3a-Acetoxy-7~-isobutyryloxytropane R R 3a-lsobutyryloxy-7~-acetoxytropane 3a-Cinnamoyloxy-7~-hydroxynortropaneR 3a-Phenylacetoxy-7~-hydroxytropane R R 3a-Hydroxy-7P-phen ylacetoxytropane R 3a-Tigloylox y-7P-acetox ytropane 3a-Cinnamoyloxy-7P-hydroxytropane R 3a-Apotropoyloxy-7~-hydroxytropane R 3a-Tigloyloxy-7~-propionyloxytropane R R 3a-Benzoyloxy-7~-acetoxytropane ( - )-3a-Tropoyloxy-6~-hydroxytropane R [ = ( - )-anisodaminel (~)-3a-Tropoyloxy-6~-hydroxytropane R ( = 6P-hydroxyatropine) R 3a-Tropoyloxy-7f3-hydroxytropane 3a-Tigloyloxy-7~-isobutyryloxytropane R R 3a-Phenylacetox y-7P-acetox ytropane

92 3a-Acetoxy-7P-phenylacetoxytropane 93 3a.7P-Ditigloyloxytropane N94 3a-Tropoyloxy-6f3-hydroxytropane

= Me, R, = acetyl, R2 = isobutyryl = Me, R, = isobutyryl, R2 = acetyl = H, R, = cinnamoyl, R2 = H = Me, R, = phenylacetyl, R2 = H = Me, R , = H, R2.~ = phenylacetyl = Me, R, = tigloyl, R2 = acetyl = Me, R, = cinnamoyl, R2 = H = Me, R, = apotropoyl, R2 = H = Me, R, = tigloyl, Rz = propionyl = Me, R, = benzoyl, R, = acetyl = Me, R, = tropoyl, R2 = H =

Me, R,

=

tropoyl, R2 = H

Me, R , = tropoyl, R2 = H Me, R, = tigloyl, Rz = isobutyryl = Me, R, = phenylacetyl, R, = acetyl R = Me, R, = acetyl, Rz = phenylacetyl R = Me, R, = R2 = tigloyl R = Me, 0, R , = tropoyl, R2 = H = =

oxide (=6P-hydroxyhyoscyamine N oxide) 95 3a-Tigloyloxy-7~-(2'-methylbutyryloxy)R = Me, R, = tigloyl, meth ylbutyryl tropane

R2 =

2-

1.

I1

TROPANE ALKALOIDS

TABLE I1 (continued) Alkaloid 96 3a-Tigloyloxy-7~-isovaleryloxytropane R

97 3a-Cinnamoyloxy-7~-acetoxytropane R 98 3a-(3’ ,4’ ,5’-Trimethoxybenzoyloxy)-7~-R

Structure = Me, R, = tigloyl, R2 = isovaleryl = Me, R, = cinnamoyl, R2 = acetyl = H, R, = 3,4,5-trimethoxybenzoyl,

R2 = H R = Me, R, = tropoyl, R2 = acetyl R = Me, R, = 3,4,5-trimethoxybenzoyl, 100 ( + )-3a-(3’,4’,5’-Trimethoxybenzoyloxy)R2 = H 7P-hydroxytropane R = Me, R, = 4-methoxyphenylacetyl, 101 3a-(4’-Methoxyphenylacetoxy)-7PR2 = H hydroxytropane ( = physochlaine) 102 3a-(Pyrrolyl-2‘-carbonyloxy)-7~-(N”- R = Me, R, = pyrrolyl-2-carbonyl, R2 = N-methylpyrrolyl-2-carbonyl meth ylpyrrol yl-2”-carbon ylox y) tropane ( = catuabine C) R = Me, R, = methylmesaconyl, 103 3a-Methylmesaconyloxy-7PR2 = tigloyl tigloyloxytropane ( = schizanthine F) R = Me, R , = methylitaconyl, 104 3a-Methylitaconyloxy-7/3R2 = tigloyl tigloyloxytropane ( = schizanthine G ) R = Me, R , = methylmesaconyl, 105 3a-Methylmesaconyloxy-7PR2 = angeloyl angeloyloxytropane ( = schizanthine I) R = Me, R , = methylitaconyl, 106 3a-Methylitaconyloxy-7PR2 = angeloyl angeloyloxytropane ( = schizanthine H) R = Me, R, = R2 = benzoyl 107 3a,7P-Dibenzoyloxytropane 108 3a-(3‘-Ethoxycarbonylmethacryloyloxy )- R = Me, R, = 3ethox ycarbony Imethacryloyl, 7P-senecioylox ytropane R2 = senecioyl ( = schizanthine A) R = Me, R, = ethylitaconyl, 109 3a-Ethylitaconyloxy-7~R2 = angeloyl angeloyloxytropane ( = schizanthine L) R = Me, R, = ethylmesaconyl, 110 3a-Ethylmesaconylox y-7PR2 = tigloyl tigloyloxytropane ( = schizanthine K) R = Me, R, = ethylitaconyl, 111 3a-Ethylitaconyloxy-7~R2 = tigloyl tigloyloxytropane ( = schizanthine M) 1 U 3a-Tropoyloxy-7~-tigloyloxytropane R = Me, R, = tropoyl, R2 = tigloyl 113“ 3a-Acetyltropoyloxy-6~-acetoxytropaneR = Me, R, = acetyltropoyl, R2 = acetyl ( = 6P-hydroxyhyoscyamine diacetate) 114 3a-Tropoyloxy-7~-isovaleryloxytropane R = Me, R, = tropoyl, R2 = isovaleryl R = Me, R, = tropoyl, R2 = 2115 3a-Tropoyloxy-7P-(2’methylbutyryl methylbutyry1oxy)tropane R = Me, R, = R2 = cinnamoyl 116 3a,7P-Dicinnamoyloxytropane R = Me, R, = 3,4,5-trimethoxybenzoyl, 117 3a-(3’,4’,5‘-Trimethoxybenzoyloxy)-7PR2 = benzoyl benzoyloxytropane ( = catuabine B) 118 3a-(3’,4‘,5’-Trimethoxybenzoyloxy)-7P- R = Me, R, = 3,4,5-trimethoxybenzoyl, R2 = N-methylpyrrolyl-2-carbonyl (N“-methylpyrrolyl-2”-carbonyloxy) tropane ( = catuabine A) 119 3a-(3’,4’,5’-Trimethoxycinnamoyloxy)- R = Me, R, = 3,4,5trimethoxycinnamoyl, R2 = benzoyl 7P-benzoylox ytropane

h ydroxynortropane 99 3a-Tropoyloxy-7~-acetoxytropane

(continued)

12



Structure

4. 3a,6P,7P-Trisubstituted tropanes The 3a,6P,7P-trisubstituted tropanes (120-135) are formally derived from the recently naturally found 3a,6P,7P-trihydroxytropane(120) (or from the corresponding nortropane).

120 3a,6P,7/3-Trihydroxytropane U 1 3a,7P-Dihydroxy-6P-tigloyloxytropane 122 3a-Tigloyloxy-6P,7P-dihydroxytropane ( = meteloidine)

R R R

127

128 129

130 131 132

133 134 135

= =

Me, R, = R2 = R, = H Me, R, = R, = H, R, = tigloyl Me, R, = tigloyl, R2 = R, = H

Me, R, = benzoyl, R, = R, = H Me, R, = R2 = H , R3 = benzoyl = Me, R, = cinnamoyl. Rz = R3 = H dihydroxytropane R = H, R, = phenylacetyl, 3a-Phenylacetoxy-6P.7PR, = R3 = H dihydrox ynortropane R = Me, R , = phenylacetyl, 3a-Phenylacetoxy-6P,7PR? = R, = H dihydroxytropane 3a-(2‘-Hydroxy-3’-phenylpropionyloxy)- R = Me, R, = 2-hydroxy-3phenylpripionyl, R2 = R, = H 6P,7P-dihydroxytropane ( = 6P,7Pdihydrox ylittorine) R = Me, R, = tigloyl, R, = H, 3a-Tigloyloxy-6P-hydroxy-7pR, = isovaleryl isovalerylox ytropane 3a,7P-Ditigloyloxy-6~-hydroxytropane R = Me, R, = R, = tigloyl, R2 = H 3a-(3’,4’,5’-Trimethoxybenzoyloxy)- R = Me, R, = 3,4,5-trirnethoxybenzoyl, R2 = R, = H 6P,7P-dihydroxytropane R = H, R, = 2-hydroxy-3( + )-3a-(2’-Hydroxy-3‘phenylpropionyl, R2 = H , R, = tigloyl phenylpropionyloxy)-6~-hydroxy-7Ptigloy lox y nortropane 3a-Acetoxy-6~,7~-dibenzoyloxytropaneR = Me, R, = acetyl, R2 = R, = benzoyl 3a-(3’,4’,5‘-Trimethoxycinnamoyloxy)-R = Me, R, = 3,4,5trirnethoxycinnamoyl, R2 = H, 6P-h ydroxy-7P-benzoyloxytropane R, = benzoyl 3a-(3‘,4’,5‘-Trimethoxycinnarnoyloxy)R = Me, R, = 3,4.5-trimethoxycinnarnoyl, R, = acetyl, 6~-acetoxy-7~-benzoyloxytropane R, = benzoyl

l23 3a-Benzoyloxy-6P,7P-dihydroxytropane R w 3a,6~-Dihydroxy-7P-benzoyloxytropaneR R 125 3a-Cinnamoyloxy-6p,7/3126

=

= =

1.

13

TROPANE ALKALOIDS


Structure

5. 3a-Substituted 6P,7P-epoxytropanes The 3a-substituted 6P.7P-epoxytropanes (136-143) are characterized by the 6P,7P-epoxy ring.

R 136 3a-Hydroxy-6@,7P-epoxytropane ( = scopine) R 137 3a-Apotropoyloxy-6P.7Pepox ynortropane (= aponorscopolamine or aponorhyoscine) 138 3a-Apotropoyloxy-6~,7~-epoxytropane R ( = aposcopolamine or apohyoscine) 139 3a-Tropoyloxy-6~,7~-epoxynortropane R ( = norscopolamine or norhyoscine) 140 ( - )-3a-Tropoyloxy-6~,7P-epoxytropaneR (=scopolamine or hyoscine) 141 (t)-3a-Tropoyloxy-6/3,7~-epoxytropaneR ( = atroscine) 142 ( - )-3a-(2’-Hydroxytropoyloxy)-6/3,7p- R epoxytropane [ = (-)-anisodine or daturamine] R 143 3a-Tropoyloxy-6P,7p-epoxytropaneNoxide ( = scopolamine N-oxide or hyoscine N-oxide)

= Me, =

H, R,

= Me, =

R, = H =

apotropoyl

R, = apotropoyl

H,R, = tropoyl

= Me,

R, = tropoyl

= Me,

R, = tropoyl

= Me,

R, = 2-hydroxytropoyl

= Me, 0, R, = tropoyl

6. 3P-Substituted 2P-carboxytropanes The 3P-substituted 2p-carboxytropanes (144-150) can be considered to be derivatives of 2P-carboxy-3P-hydroxytropane(ecgonine, 146) or of the corresponding, not yet naturally found, 2p-carboxy-3P-hydroxynortropane.

144b (-)-2P-Carboxy-3/3-formylnortropane ( =norecgonine formyl estei)

R

=

H, R, = formyl, R2 = H

(continued)

14

MAURI LOUNASMAA A N D TARJA TAMMINEN

TABLE I1 (continued) Alkaloid 145 2,3-Dehydro-2-methoxycarbonyltropane ( = A2(3)-anhydroecgoninemethyl ester or methylecgonidine) 146 ( - )-2P-Carboxy-3P-hydroxytropane ( = ecgonine) 147 ( - )-2P-Methoxycarbonyl-3Phydroxytropane ( = ecgonine methyl ester) 148 ( - )-2p-Carboxy-3P-benzoyloxytropane ( = benzoylecgonine) 149 ( - )-2p-Methoxycarbonyl-3/3benzoyloxytropane ( = cocaine) 150 (- )-2p-Methoxycarbonyl-3@cinnamo ylox ytropane ( = cinnamoylcocaine)

Structure R = Me, A2(3), R2 = Me

R = Me, R, = R2

=

H

R = Me, R, = H, R2

=

Me

R

=

Me, R, = benzoyl, R2 = H

R

=

Me, R, = benzoyl, R2

R

=

Me, R,

=

=

Me

cinnamoyl, R2 = Me

" .

7. 3a-Substituted 4a-benzvltro~anes The 3a-substituted 4a-benzyltropanes (151-155) are without functionality at C-6 and C-7.

151 3a-Acetoxy-4a-benzyltropane ( = alkaloid KD-B) 152 3a-Acetoxy-4a-hydroxybenzyltropane 153 3a-Acetoxy-4a-acetoxybenzyltropane ( = acetylknightinol) 154 3a-Benzoyloxy-4a-benzyltropane (=alkaloid KD-A) 155 3a-Benzoyloxy-4ahydroxybenzy ltropane

R, = acetyl, Rl = H R,

=

acetyl, R2 = OH

R, = acetyl, R2 = acetoxy R, = benzoyl, R2 = H R, = benzoyl, R2 = OH

8. 3a,6P-Disubstituted, 4a-benzyltropanes The 3cu-6P-disubstituted 4a-benzyltropanes (156-157) are 3a-substituted 4abenzyltropanes with an additional functionality at C-6.

15

1 . TROPANE ALKALOIDS TABLE I1 (conrinued) Alkaloid

156 3a-Acetoxy-4a-benzyl-6phydroxytropane ( = knightoline) 157 3a-Cinnamoyloxy-4a-benzyl-6phydroxytropane (=alkaloid KD-D)

Structure

R,

=

acetyl, R2

R,

=

cinnamoyl, R2 = R3

=

R3

=

H =

H

9. 3a,7p-Disubstituted 4a-benzyltropanes The 3a,7p-disubstituted 4a-benzyltropanes (158-160) are similar to those of the preceding group except that the additional functionality is at C-7 instead of C-6.

R3°Q& R2

\

158 3a-Hydroxy-4a-benzyI-7pR , = R2 = H, R3 = benzoyl benzoyloxytropane (=alkaloid KD-C) 159 3a-Cinnamoyloxy-4a-hydroxybenzyl-7p-R, = cinnamoyl, R2 = OH, R, = benzoyl benzoyloxytropane ( =alkaloid KD-E) R, = H, R2 = OH, R, = benzoyl 160 3a-Hydroxy-4a-hydroxybenzyl-7pbenzoyloxytropane ( =alkaloid KD-F) 10. 3P,6P-Disubstituted 4a-benzyltropanes The 3/3,6p-disubstituted 4a-benzyltropanes (161 and 162)are the only 4a-benzyltropanes where the C-3 substituent is p.

161 3~-Hydroxy-4a-hydroxybenzyl-6~R, acetoxytropane ( = knightalbinol) 162 3~-Benzoyloxy-4a-hydroxybenzyl-6p- R, hydroxytropane ( = knightolamine)

=

H, R2 = OH, R, = acetyl

=

benzoyl, R2

=

OH, R, = H

(continued)

16



Structure

11. Pyranotropanes The natural products 163-166 contain a y-pyrano group attached to the 3,4-position of the tropane ring.

Me\

R1

163 Pyranotropane ( = strobiline) 164 10-Methylpyranotropane ( = bellendine) 165 1 I-Methylpyranotropane ( = isobellendine)

166 10,l I-Dimethylpyranotropane

R, = R2 = H R, = Me, R2 = H R , = H, Rz = Me R, = R2

=

Me

( = darlingine)

12. 3,4-Dihydropyranotropanes Compounds 167-168 are y-pyranotropane derivatives in which the 3,4-double bond is reduced.

MI?

\

D F H H

'O

167 1 I-Methyl-3,4-dihydropyranotropane ( = 5,ll-dihydroisobellendine) 168 lO,ll-Dimethyl-3,4dihydropyranotropane ( = 5 , l l dihydrodarlingine)

R, = H, R2 = Me R, = R2 = Me

11

1.

17

TROPANE ALKALOIDS


Structure

13. l0,ll-Dihydropyranotropanes The 10,l I-dihydropyranotropanes (169-174)are y-pyranotropanes in which the 10,I I double bond is reduced. It has not been possible to deduce from the data available whether the C-10 and/or C-ll substituents, when present. are Q or P .

169 10,I I-Dihydropyranotropane

Rl

=

R2

R,

=

Me,,, Rz = R,

=

H

171 10-Methyl-10,lI-dihydropyranotropane R ,

=

Me,,, R2

R,

=

H

R,

=

Rz = Meeg, R,

=

H

R,

=

R3

Ph,,

R1

=

H, R2

=

R,

=

H

( = dihydrostrobiline)

170 10-Methyl-10,ll-dihydropyranotropane ( = dihydrobellendine)

=

( = epidih ydrobellendine)

172 10,l I-Dimethyl-10.1 I dih ydropyranotropane ( = 2,3-dihydrodarlingine) 173 11-Phenyl-l0,ll-dihydropyranotropane ( = strobamine) 174 7P-Hydroxy-l I-phenyl-l0,11dihydropyranotropane ( = strobolamine)

=

H, R2 =

=

Ph,,, R,

=

OH

14. Miscellaneous tropanes The following heterogeneous group contains I3 "monomeric" compounds (175-187) not falling in any of the 13 preceding groups. Some, however, are apparent precursors for compounds mentioned earlier [e.g., chalcostrobamine (187)for strobamine (173)l.

175 3-Oxotropane

( = tropinone)

(continued )

18


TABLE I1 (confinued) Alkaloid

Structure

176 Ip-Hydroxytropane (hydrochloride) ( = physoperuvine) OH

177 2P,6P-Dihydroxynortropane ( = baogongteng C)

m$ OH H

H

6

H\

FH

H

178 2P,7P-Dihydroxynortropane ( = erycibelline)

OH H

179 Ip,2a,3P-Trihydroxynortropane ( = calystegine A,) H r

Y

180 ( + )-3,4-Dehydro-4-acetyltropane ( = ferruginine)

Me

1.

19

TROPANE ALKALOIDS


Structure

181 Ip,2a,3/3,6P-Tetrahydroxynortropane (=calystegine B,)

mgH OHH

H

OH

a

182 lp,2a,3P,4cr-Tetrahydroxynortropane ( = calystegine B2)

q; OHH

OH

183 ( - )-2P-Hydroxy-6P-acetoxynortropane ( = baogongteng A)

184 ( + )-4a-Benzoyltropane ( = ferrugine)

(continued)

20


TABLE 11 (conrinued) Alkaloid

Structure

185" (+)-2a-Benzoyloxy-3Phydrox ynortropane

186 6,7-Dehydro-3~(4'hydroxybenzoy1oxy)tropane [ = 3a-(4hydroxybenzoyloxy)trop-6-ene]

19;

7

6

0

Me

\

I

OH

I k

OH

187 ( + )-3,4-Dehydro-4-cinnarnoyl-3hydroxytropane ( = chalcostrobarnine)

0

Q I

1.

21

TROPANE ALKALOIDS


Structure

15. “Dmeric” and “trimeric” tropanes Fifteen “dimeric” tropane alkaloids (188-202) and one “trimeric” tropane alkaloid (203) have been found so far. 188 Schizanthine C

189 Schizanthine D

A 190 Schizanthine E

(continued)

22

MAURI LOUNASMAA A N D T A N A T A M M I N E N


Structure

191 a-Belladonnine

Me.

192 P-Belladonnine

Me.

II 0

193 a-Scopadonnine

23

1. TROPANE ALKALOIDS TABLE I1

(continued)

Alkaloid

Structure

194 p-Scopadonnine Me.

195 Schizanthine B Me,

C-Me

I Me

l . -

I

Me

H Me-?

-0

L"

he

1% Schizanthine X

(continued)

24


TABLE I1 (continued) Alkaloid 197 7-Acetoxytropan-3-yl tropan-3’-yltruxillate

198 Subhirsine

199 Convolvidine

Structure

1.

25

TROPANE ALKALOIDS

TABLE 11 (confinued) Alkaloid

200 7-Acetoxytropan-3-yl 7’-hydroxytropan3’-yl-truxillate

HO,

0-

201 a-Truxilline

202 P-Truxilline

Structure


Structure

203 Grahamine

$=-

Phenylladc acid

OH CH,--F-*~--S-CoA I

H

O

F‘henyllactoyl-CoA

1 (-t

#H3

H CH*-y-*$-O I OH 0

Hyoscyamine

Littorine

SCHEME 10. Proposed pathway for the incorporation of phenylalanine into hyoscyamine and littorine.

represents a specific activity of tropane alkaloid metabolism, as in plants the pathway to phenylalanine proceeds via prephenate and arogenate, not phenylpyruvate as it can in bacteria (107). Obtaining further information about the enzyme has remained difficult, however, and it is only recently that a phenylalanine aminotransferase from a tropane alkaloid-producing species has again been reported, this time from transformed roots of H. albus (108). No further details are currently available. Aminotransferases showing activity with phenylalanine have been reported from plants of other genera (109), though their relevance to phenylalanine metabolism is unclear (see Refs. 107 and 110). To date, no enzyme responsible for the reduction of phenylpyruvate to phenyllactate has been described. This is somewhat surprising in view of the ease with which NADPH-linked oxidoreductases can be assayed; however, attempts to measure this reductase in H. albus root cultures have so far proved unsuccessful (111). Phenylpyruvic acid is readily incorporated into tropane alkaloids (112). It has been shown in root cultures of D.stramonium that [3’-*H2]phenylpyruvic acid is incorporated into both hyoscyamine and littorine with the predicted retentions of one and two 2H atoms/molecule, respectively.

,

2.

BIOSYNTHESIS OF TROPANE ALKALOIDS

153

Incorporation was determined by G U M S on a DB-17 column, which fully resolves these isomeric alkaloids (78). Similarly, the incorporation of phenyllactic acid into littorine and hyoscyamine has been clearly established (103). Woolley and colleagues acid was converted to showed that ( R S ) - [l’,3’-’3C,,3‘-’4C]phenyllactic hyoscyamine by whole plants of Datura (98,100).More recently, we have shown that ( R S ) - [1’ ,3’-’3C2]phenyllacticacid was incorporated into hyoscyamine in transformed root cultures of D.stramonium with a specific incorporation of about 60% (113). Similarly, this compound was incorporated into littorine, hyoscyamine, 6-hydroxyhyoscyamine, hyoscine, apoatropine, and apohyoscine by root cultures of a Datura hybrid (101) at levels of up to 65% specific incorporation. In both experiments, coupling in the tropate moiety between the 1’- and 3’-I3C nuclei of phenyllactic acid was shown by NMR, indicating that the predicted shift in carbon bonding had occurred. Only littorine showed no coupling, as expected. In parallel experiments in which ’H-labeled (RS)-phenyllactic acids were fed to D. stramonium and Anthocercis littorea root cultures, it was demonstrated that (RS)-[3-2H2]-,(RS)-[2-,H]-, and (RS)-[2-2H,3-2H2]phenyllactic acids all gave rise to ’H in littorine and hyoscyamine at the level predicted if this molecule were incorporated directly or following a C- 1’-C-2’ to C1’-C-3’ bond rearrangement (78). In Datura, the retention of the 2-% in hyoscyamine (23%) and littorine (18%) was similar, suggesting that phenyllactic acid was not metabolized via phenylpyruvic acid. Some loss of the 2-’H might be expected, however, as the phenyllactate dehydrogenase reaction is likely to be reversible. Thus, incorporation from the C2‘ might be lower than from the C-3’, but this has yet to be confirmed by ’H NMR. The analysis is further complicated by the possible loss of some 2-’H in hyoscyamine by racemization. Furthermore, we have found that both (R)-[l’,3‘-’3C2]-and ( S ) - [I ’,3’-’3C2]phenyllacticacids are incorporated into hyoscyamine by D . stramonium root cultures at equivalent levels (113). This may indicate that racemization of the phenyllactate takes place in uiuo during the feeding period. These apparently conflicting results need to be resolved. In cultures of D . strarnonium, it has been found that the (R) isomers of P-phenyllactic acid, mandelic acid, and 2-phenylpropionic acid are less toxic than the (S) isomers (78). This may indicate a greater ability to metabolize the (R) isoforms, since the toxicity of these compounds is usually a general effect of acidity. Interestingly, feeding either (RS) or (R)-phenyllactic acid increased the littorine level, but not the hyoscyamine content, of these cultures (78,113).The isolation of the enzymes concerned along with study of their properties in uitro will enable a clearer picture to be established of the exact pathway.

154

RICHARD J . ROBINS A N D NICHOLAS J . WALTON

Despite these uncertainties, however, it seems reasonable to argue that this pathway involves the metabolism of phenylalanine to phenylpyruvate and, subsequently, phenyllactate. In contrast, the route by which phenyllactic acid is metabolized to hyoscyamine is much less clear-cut. That the C-2’ of phenylalanine forms the carboxymethyl group of hyoscyamine was elegantly established by Leete and Louden (95). Exactly when, and how, the carbon group migration occurs is undescribed, as is the mechanism of ester formation (see Section VI1,B). What has been established is that the carbon shift does not involve the oxidation of the C-2’-C-3’ bond. The 3-2Hand 2-2Hlabels are both retained during the rearrangement, indicating that double bond formation has not occurred (78,97).The intermediacy of an epoxide has not, however, been ruled out. Recent experiments examining the incorporation of label from phenylpyruvic, phenyllactic, and tropic acids into tropoyl-tropanes have caused the putative role of free tropic acid in hyoscyamine biosynthesis to be questioned (see Section X,A). A considerable effort in enzymology is clearly required to establish the metabolic events occurring in the conversion of phenyllactic acid to hyoscyamine. It may be, for example, that the rearrangement in the side chain takes place after the activation of phenyllactic acid, possibly as the CoA thioester (Scheme 10). Not unexpectedly, the benzoic acid component of cocaine is derived from phenylalanine (124,115). Although, for example, the properties of phenylalanine ammonia-lyase (PAL), responsible for the conversion of phenylalanine to trans-cinnamic acid during cocaine biosynthesis in E. coca, are likely to be similar to those of PAL characterized from other plant sources (116), there is no specific evidence on this point. B. FORMATION OF OTHERESTERIFYING ACIDS Besides tropic and phenyllactic acids, a wide range of other acids are found esterified with tropane bases (4). These range from such common and simple compounds as formic and acetic acids to highly unusual molecules, such as the sulfur-containing 1,2-dithiolane-3-carboxylicacid, the esterifying acid in brugine, an alkaloid of the Rhizophoraceae (117). The structures of the esterifying acids found in the tropane alkaloids have been thoroughly reviewed previously (4) in this treatise (see also Chapter 1, this volume) and need not be repeated here. Limited labeling evidence is available on the origin and likely biosynthetic pathway of these acids. Tiglic acid, the acidic component of tigloidine and meteloidine, has been shown to be derived from isoleucine, probably via 2-methylbutanoic acid (Scheme 11) (2,118-120) and not via trans-2,3-dimethylacrylic (angelic) acid, as is apparently the route for

2.

Angelic acid


Tiglic acid

155

2-Hydroxy-2-methylbutanoic acid

SCHEME 1 1 . Pathway of tiglic acid formation from isoleucine.

heliosupine formation in Cynogfossum(121). N o specific biochemical characterization at the cell-free level has been reported, however, and, where a particular reaction or sequence of reactions is not shared with a wellcharacterized pathway, no information at all is available directly. In the case of tiglic acid formation, this reflects the lack of detailed characterization of the catabolic pathway for isoleucine in plants, though this pathway has been well studied in animals and bacteria (122). It is likely that the final stage of esterifying acid addition involves the formation of CoA thioesters, since, in the few cases where evidence is available, the esterifying reactions use the CoA esters as substrates, as discussed below (see Section VII).

VII. Formation of Tropeines The reactions described in Sections V and VI result in the biosynthesis of the two intermediates that constitute the alkamine and acidic moieties which are brought together as an ester in the tropeines. The reactions by which the ester bonds are formed have remained essentially uncharacterized until recently. A number of reported properties of esterases appear more related to tropane ester hydrolysis (see Section IX). It has now been demonstrated, however, that a number of esters can be formed in uitro by acyltransferase reactions involving the transfer of the acidic group

156

RICHARD J. ROBINS A N D NICHOLAS J . WALTON

from the relevant coenzyme A thioester to tropine or pseudotropine. The reactions by which the CoA thioesters are formed have yet to be described. ACIDS A. ESTERSOF ALIPHATIC Although in D. stramonium root cultures (see Section II,B) the dominant alkaloid is hyoscyamine, the roots accumulate substantial quantities of acetyltropine in response to feeding with tropine or tropinone (21). Callus cultures of D. innoxia also accumulate acetyltropine when fed tropine (123, whereas suspension cultures of Duboisia myoporoides produce both acetyltropine and isobutyryltropine (25). Similarly, some enhanced tiglyltropine formation occurs when tiglic acid is fed to a Datura hybrid (22). The ability of these cultures to make high levels of acetyltropine led us to investigate the acetyl-CoA: tropine acyltransferase activity present in D. strumonium root cultures in the anticipation that, by understanding the properties of the enzyme, it might be possible to define the conditions required to assay hyoscyamine biosynthesis successfully. A preliminary analysis of extracts of 10-day-old roots indicated that enzymes able to esterify tropine and pseudotropine with acetyl-CoA were present (124). Surprisingly, considering that the a series of tropane alkaloids strongly dominates in this species, the activity with pseudotropine was 5- to 10fold higher than that with tropine. The acetylation of tropine and pseudotropine by extracts of D. stramonium roots shows maximal activity at pH 8.5-9.5 and only about 20% of this level at pH 7. This may indicate that tropine needs to be in the neutral state to act as substrate for the enzymes. The reaction transfers an acetyl unit to the C-3 hydroxyl of the substrate, and the nature of the products has been confirmed by cochromatography of the products derived by incubating ['4C]tropine or ['4C]pseudotropine with unlabeled acetyl-CoA with the products formed by incubating [ I-'4C]acetyl-CoA with tropine or pseudotropine (124). On G U M S , the products of tropine or pseudotropine acetylation co-elute with authentic synthetic standards and show the same fragmentation characteristics. Preliminary studies of the two activities show there to be two separable enzymes present (124). It is possible to obtain a fraction from anionexchange chromatography containing only the acetylpseudotropineforming activity. The tropine-acetylating activity has not, however, been obtained free of any pseudotropine-utilizing enzyme. In crude extracts it shows apparent K , values of 0.22 and 0.24 mMfor acetyl-CoA and tropine, respectively. The observed acetylation of tropine in suspension cultures of D. innoxia (123) has also been further examined. Unpublished studies (125) of this

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system showed an activity to be present that acetylated tropine with acetyl-CoA and which peaked at the maximum growth rate of the culture. The product was confirmed by crystallization to constant specific activity to be 3-acetyltropine. In contrast to the D. sframonium enzyme, activity appeared to be highest at pH 7.5. Whether this represents a different enzyme activity from that found in D. sframonium roots has yet to be resolved. A further activity that forms P-tigloxyltropane (tigloidine) from tiglylCoA and pseudotropine has also recently been found in root cultures of D. stramonium ( I 26). Again, although tigloxyltropane extracted from roots of this species is predominantly (-80 : I ) the 3a stereoisomer, the activity that forms the 3p isomer is present at high levels in the extracts. Only a trace of 3cu-forming activity can be detected. The enzyme has been purified about 100-fold by sequential ammonium sulfate precipitation, hydrophobic interaction chromatography, anion-exchange chromatography, and chromatofocusing. The activity that forms 3-acetylpseudotropine copurifies with the 3-tiglylpseudotropine-formingenzyme to about the same level of purification. At present, it appears that a single enzyme may be responsible for both activities, based on the copurification and kinetic experiments that indicate competitive kinetics between acetyl-CoA and tiglyl-CoA. The enzyme shows a K , of 0.30 mM for acetyl-CoA, similar to that of the tropine-acetylating enzyme. The K, of 1.1 mM for tiglylCoA is rather higher, but the V,,, is very much greater. The similarities of the K , values for pseudotropine (0.34 mM with tiglyl-CoA and 0.36 mM with acetyl-CoA) supports the conclusion that this is a single activity. The enzyme shows a high degree of specificity for the alkaloidal substrate, being active only with pseudotropine (100%) and 4-hydroxy-lmethylpiperidine (14%). In this respect it is dissimilar to TR I and TR 11, with the latter enzymes showing a broader substrate specificity. With the acyl-CoA thioester, however, a broad range of substrates was utilized, although all at rates of less than 10% that of tiglyl-CoA. The range of acyl groups accepted could indicate that the wide range of aliphatic esters found (4) is derived from the activities of a small number of broad-specificity acyltransferases. The differences in the apparent affinities of the 3a-forming and 3pforming enzymes for the CoA thioesters and 3-hydroxyltropane bases may also be an important factor in determining the alkaloidal spectrum formed in uivo. In D. stramonium, TR I activity is 5- to 10-fold higher than that of TR I1 (82,87),and the tropine to pseudotropine ratio is typically about 30 : 1. Thus, even though the total potential enzyme activity as determined in uitro is much lower for 3cu-acetylation than for 3p-acetylation, the availability of the substrate, coupled with the slightly greater affinity of

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RICHARD J . ROBINS A N D NICHOLAS J . WA LTO N

the 3a-acetylating enzyme for acetyl-CoA or of the 3P-enzyme for both its substrates, establishes conditions in which the 3a-acetyl is the favored product. A similar situation may arise with 3-tigloxyltropane formation, but this analysis awaits the description of the tiglyl-CoA:tropine acyltransferase enzyme.

B. HYOSCYAMINE A N D OTHERAROMATIC ESTERS The formation of the tropoyl ester of tropine, hyoscyamine, is, in many species, quantitatively the dominant metabolic reaction involving tropine esterification in v i m . Investigations in the early to mid 1960s claimed to measure ester formation, but these results have subsequently failed to be substantiated. Extracts of whole leaves of wild D. srramonium plants and of 2- to 3week-old cultured seedlings were used by Kaczkowski to prepare enzyme extracts (127). Following ammonium sulfate fractionation and DEAEcellulose chromatography, he reported the separation of a tropine esterase (see Section IX) from a synthesizing activity. The 75-100% saturated ammonium sulfate cut was described as having an “irregular but considerable” activity. When the desalted extract was incubated at pH 6 (0.2 M phosphate buffer) with 6 p M tropine and 6 p M tropic acid, 1 mg/1.7 ml ATP, and traces of Mg2+and Mn2+,up to 3% of the substrate was reported to have been converted to hyoscyamine. The reaction was optimal at pH 6, 25”C, and with 6 p M substrates, higher levels causing a loss of activity. The report concluded that “atropine synthase” had only been found because of the successful separation of this enzyme from atropine esterase, which was reported present at a 7-fold higher level. There appear, however, to be a number of problems associated with the findings of Kaczkowski, and later workers have had difficulty reproducing the results. The extracts were made from the leaves, yet synthesis is known to occur in roots. The “irregular” nature of the occurrence of hyoscyamine might indicate contamination with alkaloid from the tissue, which we know can be carried through a number of purification stages tightly bound (nonspecifically) to protein. Yet the rates Kaczkowski obtained tend to preclude this possibility. Another reason to question these reports, however, is the improbability that tropine and tropic acid, even in the presence of MgATP, are combined directly. Evidence obtained subsequently from numerous other biological ester-forming systems shows that the acid is normally activated, frequently as the CoA thioester. Jindra and co-workers recognized a number of these deficiencies and reinvestigated this work. They incubated the expressed sap of D.srrumonium roots with tropine and tropic acid, but without effect (128). The addition of CoA and ATP to the reaction mixture did not stimulate biosyn-

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thesis (129). Subsequently, however, in a brief communication, success was claimed using extracts made from 27- or 31-day-old D. stramonium suspension cultures (105). Expressed juice was concentrated 10-fold by lyophilization and incubated with 30 mM tropic acid, 30 mM tropine, 5 mg/ml ATP, and 0.15 mg/ml CoA at pH 7. After 6 to 48 hr, samples were analyzed and found to contain hyoscyamine by cochromatography. The amount present appeared to increase with time, and no product was found in boiled extracts or when reactions were incubated at pH 5.3. Details of these experiments have not been published (106), and neither has the report, made simultaneously, that the suspension cultures would convert added tropine and tropic acid to hyoscyamine. In view of the findings of later workers, both these claims need to be substantiated by further analysis. The potential role of tropoyl-CoA in hyoscyamine formation led to the development of a synthetic route for this putative intermediate in which tropic acid is first activated as the N-hydroxysuccinimide ester (yield 50%) and tropoyl-CoA made by transesterification with free CoA (yield -35%) (130).Incubations made with this substrate, however, have proved ineffective (83,131,132). Nevertheless, it is likely that a CoA thioester is involved. The role of thioesters in the acyl transfer of aromatic groups is well established for the phenylpropanoid pathway (68). In recent work, an enzyme activity in transformed root cultures of D. stramonium has been identified that acylates pseudotropine with phenylacetate from phenylacetyl-CoA and with benzoate from benzoyl-CoA (132). Furthermore, when labeled benzoic acid was activated as the S-(2acetamidoethyl)ester, incorporation rates into cocaine were greatly improved (133). Interestingly, N-methylecgonine was not benzoylated by the extract from D. stramonium, indicating that a quite separate enzyme, able to accept the presence of the 4-carboxyl group, is probably present in Erythroxylon species. An intriguing possible alternative route was investigated by McGaw and Woolley (134). They argued that esterification might occur prior to cyclization if hygrine were reduced first to hygroline (Scheme 12). The

@ - @ - @ H3C,N,6 C II 0

Hygrine

N = H3C\yC

H I ‘OH

Hygroline

N : H3C\C/C

H

-

\

/,c - CH3

C - CH3

H’ ‘ W C - 7 II 0 CH3

Tiglylhygroline

It

0

\ CH3

3-Tigloyloxytopane

SCHEME 12. Proposed hygroline/tiglylhygnne pathway.

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RICHARD J . ROBINS AND NICHOLAS J . WALTON

hypothesis was tested by feeding intact D . meteloides plants with [1',2'''C2]tigloyl hygrine and found not to be valid, as the 1 ' : 2' ratio of I4C was not maintained in the tigloxytropane esters, as shown by degradation.

VIII. Metabolism of Tropeines A. CONVERSION

OF

HYOSCYAMINE TO HYOSCINE

In many whole plants, and some root cultures, the major product that accumulates is not hyoscyamine, but the 6,7-P-epoxide, hyoscine. The conversion of hyoscyamine to hyoscine is the most thoroughly investigated part of the pathway at the biochemical level, with a series of studies since the late 1980s having resulted in the purification of the pertinent activities, the clear demonstration of the mechanism of the reaction, and the cloning of a gene. This work demonstrates effectively how biochemical studies can clarify uncertainties that cannot be resolved by chemical labeling studies alone. Prior to this biochemical analysis, the route by which the conversion occurred was not clear. Feeding experiments with 6,7-dehydrohyoscyamine in a Daturaferox scion showed that this compound was efficiently incorporated into hyoscine, but not hyoscyamine (135). When [N-methyl14C,6P,7P-3H2]tropine was fed to whole plants of D . innoxiu and D . metebides, both 3Hatoms were lost (136), supporting the proposed intermediacy of the 6,7-dehydro compound. Two alternative pathways were proposed (see Scheme 13). One pathway suggested that hyoscyamine is first dehydrated and then hydrated to 6-hydroxyhyoscyamine, this subsequently being oxidized to form the 6,7-epoxide (137);the other pathway hypothesized that 6-hydroxyhyoscyamine is formed directly from hyoscyamine followed by dehydration to 6,7-dehydrohyoscyamine and subsequent conversion to hyoscine. A flaw in both schemes was the complete absence of the putative dehydro intermediate in alkaloid extracts made from hyoscine-forming species. In any event, neither scheme proved correct, although it is the case that the first event is the hydroxylation of hyoscyamine to form the 60hydroxy derivative. The correct sequence of reactions can be assigned on the basis of the enzymology. In 1986, Hashimoto and Yamada (138) described an enzyme (hyoscyamine 6P-hydroxylase, H6H) in extracts of root cultures of Hyoscyamus niger that would carry out this reaction. The enzyme shows an absolute requirement for molecular oxygen, Fez+,2-

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6,7-~ehydmhyoscyamine

SCHEME 13. Alternative routes for the conversion of hyoscyamine to hyoscine.

oxoglutarate, and hyoscyamine. I n uitro,the activity is also stimulated 3to 6-fold by ascorbic acid, but it is not clear whether this effect is due to its acting to maintain the iron in its Fe(1I) oxidation state or is due to some other effect on the enzyme reaction mechanism. The reaction shows a I : 1 stoichiometry between the production of 6P-hydroxyhyoscyamine, as determined by GC, and the decarboxylation of 2-oxoglutarate to succinate, as determined by the loss of 14C02from 2-[l-'4C]oxoglutarate. The reaction product was confirmed to be (-)-6P-hydroxyhyoscyamine by G U M S , NMR, melting point, and ORD. The presence of this activity correlated well with the ability of cultures to make hyoscine de nouo. It shows variable activity with the age of the cultures, showing a peak of activity about 7 days after switching the cultures to IBA-free medium (139). The H6H in Datura similarly shows a peak during the growth of the cultures (22). Following a purification of about 300-fold (17% yield) by sequential hydrophobic interaction, ion-exchange, and hydroxyapatite chromatographies, the properties of the enzyme were described in detail (139). The enzyme appears to be a monomer with a molecular weight of about 41,000. The activity is maximal at about pH 7.8 and shows a moderately high affinity for both its organic substrates, with a K , of 35 p M f o r hyoscyamine and a K , of 43 p M for 2-oxoglutarate. Although the specificity for 2oxoglutarate was very high, hyoscyamine could be replaced by a number

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RICHARD J . ROBINS A N D NICHOLAS J . WALTON

of other tropanes, some of which were inhibitors of hyoscyamine hydroxylation (Table IV). The enzyme showed good activity with a number of nor compounds, and there appeared little requirement for the carboxymethyl group of the tropate moiety. The nonnatural analog homatropine was readily hydroxylated. In all cases, the enzyme showed complete regiospecificity, the reaction placing a hydroxyl only at the C-6 position. It also showed an absolute requirement for the ester to be 3a and to have the d configuration. With the exception of Mg2+and Ca*+,the enzyme appeared to be completely inhibited (>95% at 0.4 m M ) by all other divalent metal ions tested. Surprisingly, however, in view of the putative role of ascorbate, Fe3+inhibits activity only by about 30%. Like other known 2TABLE IV SUBSTRATE SPECIFICITY OF HYOSCYAM~NE 6P-HYDROXYLASE FOR ALKALOIDAL SUBSTRATES" Relative activity Substrate

(9%)

Product

I-Hyosc yamine Tropine Acetyltropine lsobut yry ltropine Apoatropine I-Norh yosc yamine Noratropine-N-acetic acid Noratropine-N-butyric acid Atropine methyl bromide Phenylacet yltropine 2-Phenylacrylylpseudotropine Phenylalanyltropine tert-Cinnamoy ltropine

100

( - )-6P-Hydroxyhyoscyamine

p-H ydroxyatropine I-Homatropine 2-H ydrox y-3-phen ylpropion y ltropine 3-H ydrox y-3-phenylpropionyltropine 6.7-Dehydrohyoscyamine

0 1

I5 45 81 17 0 1

81

3 8 39 26 81 15 56 119

-

nd nd 6-H ydrox yapoatropine 6-H ydrox ynorh yosc yamine nd

-

nd 6-H ydrox yphen ylacet yltropine nd nd terr-Cinnamoyl-6h ydroxytropine nd 6-H ydrox yhomatropine 2-H ydroxy-3-phenylpropion yl6-h ydrox ytropine 3-H ydrox y-3-phenylpropionyl6-h ydrox ytropine Scopolamine

Inhibition (%Y ndd nd nd nd 29 nd 19 nd nd 12 nd nd nd nd 8 nd

nd 32

" Data from T. Hashimoto and Y. Yamada, Eur. J . Biochem. 164, 277 (1987): Y . Yamada and T. Hashimoto, Proc. J p n . Acad. 65B, 156 (1989). Activities (relative to that observed with I-hyoscyamine) were measured in the presence of each alkaloid at 0. I mM. Percentage inhibition of I-hyoscyamine hydroxylation with an inhibitor concentration of 0.2 m M . nd, Not determined.

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163

oxoglutarate/Fe2+-dependentdioxygenases, H6H is totally inhibited (>92% at 0.1 mM) by superoxide scavengers such as nitro blue tetrazolium. The availability of purified hyoscyamine 6P-hydroxylase enabled studies to be performed that clarified the aberrant metabolism of 6,7-dehydrohyoscyamine previously observed. In uitro, this compound proved to be an excellent substrate for H6H, being converted to hyoscine. Thus, it was still conceivable that 6,7-dehydrohyoscyamine was an intermediate in viuo. This possibility was eliminated, however, by examining the metabolic fate of I8O in [6-'80]hydroxyhyoscyamine (140). The labeled intermediate was prepared by incubating I8O2with an extract of H6H from H . niger. An incorporation of 85% was obtained based on the isotope ratios determined by derivatized G U M S analysis. The metabolism was tested in shoot cultures of Duboisia myoporoides, themselves unable to make hyoscine but previously demonstrated to convert hyoscyamine efficiently to 6-hydroxyhyoscyamine and hyoscine (26). The hyoscine extracted from the shoots after 6 days of feeding showed an isotopic ratio of 84.6%, indicating that complete retention of the 6-0 occurs during epoxidation. This finding fully supports that of Leete and Lucast (136). Furthermore, when [7P-*H]6P-hydroxyhyoscyamine was fed to D . myoporoides shoot cultures, all the 2H was lost on conversion of the substrate to hyoscine (141).

What has proved much more difficult to establish, however, has been the nature of the epoxidase enzyme. Experimentally, it has proved impossible to separate the hyoscyamine-hydroxylating activity from the 6-hydroxyhyoscyamine epoxidase activity (139,142). The latter enzyme shows a similar absolute requirement for 2-oxoglutarate and Fe", stimulation by ascorbate (about 3-fold), and sensitivity to divalent metal ions. During molecular exclusion chromatography, the activities were found to coelute at 41,000 D, and the two activities eluted in the same fractions from both hydrophobic interaction and ion-exchange columns. In the course of purification, however, the epoxidase activity was substantially lost. In a crude extract, the ratio of the specific activities was 2.3 : 5 . 3 in favor of the hydroxylase, but after purification a ratio 3.3 : 255 was observed (139). Thus, the epoxidase appears to be much less stable than the hydroxylase. Nevertheless, an indication that the two activities may be associated with a single protein is that both hyoscyamine 6P-hydroxylation and 6,7dehydrohyoscyamine epoxidation were found to be inhibited in parallel by a monoclonal antibody raised to purified H6H protein (143,143~).Furthermore, when the H6H clone (see Section XI) is expressed in transgenic, hyoscyamine-rich A . belladonu plants (83,1449,the major product accumulated is hyoscine, not hyoscyamine, as found in control plants. This could

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RICHARD J. ROBINS A N D NICHOLAS J. W A L T O N

result from an abundance of epoxidase activity in the plants and a deficiency of only the hydroxylase. However, when the clone was expressed in Nicotiana tabacum, which cannot normally make these products, hyoscine accumulated in response t o feeding hyoscyamine or 6-hydroxyhyoscyamine (83), indicating that epoxidase activity was present. Thus, it appears that both activities are indeed the property of a single protein.

B. FURTHER ESTERIFYING REACTIONS The introduction of a 6p-hydroxyl into tropane alkaloids occurs in many instances other than hyoscyamine (4). Because hyoscyamine 6phydroxylase does not act on tropine as a substrate (139), it is apparent that other enzymes must be present that catalyze the formation of 6pand 7p-hydroxyltropanols and esters. Although no enzymology is available for the formation of these compounds, some interesting indications of possible activities are available. By examining the results from D. innoxia and D. meteloides plants (145-147) challenged with 3c-w-tigloxyltropane labeled with I4C in both the alkamine and acidic moieties and with I4Clabeled tiglic acid, and from the findings of competitive feeding experiments, it proved possible to propose an ordered metabolic sequence to the di- and trioxygenated tropanes and, in particular, to deduce which reactions were unlikely to take place. It is also conceivable that the further oxygenation actually occurs prior to reduction of the 3-one, since 6P-hydroxytropan-3-one is a substrate for both TR I and TR I1 (87). When extracts of D. stramonium root cultures were incubated with 6phydroxytropan-3-one and tiglyl-CoA, no 6/3-tigloxyltropan-3-onecould be detected, however (132). Unraveling these complex hydroxylations and tigloylations will prove extremely challenging.

IX. Degradation and Oxidation of Tropeines

In contrast to the increasing information on the biosynthesis of the tropane alkaloids, their degradation remains a comparatively neglected field. To obtain a clear picture in whole plants, it is necessary to distinguish between degradation and translocation. If the total alkaloid content of a plant is not determined, it cannot be concluded that a decrease in the alkaloid content of a particular organ does not simply reflect the movement

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of alkaloid to other sites within the plant (see Section X). Convincing evidence of the occurrence of tropane alkaloid degradation has, however, been obtained both in studies using isolated organs and, perhaps more satisfactorily, in experiments using labeled alkaloids wick-fed to whole plants. Neumann and Tschope (148) reported evidence for the degradation of alkaloids in plants of a number of solanaceous species, including Atropa belladonna, Withania somnifera, Cyphornandra betacea, and Nicotiana glauca. There appeared to be substantial degradation of atropine fed to isolated leaves of Withania and Cyphomandra, in both the light and the dark. When [ l’-I4C]atropine was fed to isolated leaves of Cyphomandra betacea, almost 45% of the label was recovered after 24 hr in neutral organic substances. It was therefore suggested that, following ester hydrolysis, an early step in atropine degradation might be the decarboxylation of the resulting tropic acid. Hamon and Youngken (149) later investigated the degradation of [3H]atropine in mature D. innoxia plants. They found that almost 60% degradation of the alkaloid occurred during the first day and that after 20 days only 1.5% of the label remained in the alkaloid fraction. Because this degradation could also be shown in maturing plants, the total alkaloid contents of which were increasing, it was concluded that synthesis and degradation might occur simultaneously. Alkaloid degradation has not yet been studied directly in transformed root cultures. Circumstantial evidence for its occurrence has come from alkaloid determinations in D. strarnoniurn cultures that have been induced to differentiate by being subcultured in media containing NAA and kinetin (23; see also Section X,A). A rapid decline in alkaloid content occurs which, in apparent contrast to the situation in cultures of Nicotiana rustica (150), cannot be ascribed entirely to dilution of the alkaloid present at subculture. It is also noticeable that the ratio of alkaloids changes; in particular, there is a much greater loss of hyoscyamine than of 3-acetyltropine (see Section X,A). Data from these experiments are summarized in Table V. It is probable that the initial step in tropane-alkaloid degradation is ester hydrolysis. Cleavage of atropine to tropine and tropic acid was studied by Jindra and co-workers (128,151). Esterase activity catalyzing this reaction was found in the sap prepared from roots of D. strarnonium plants; the highest activity was obtained from plants approximately 24 weeks old, at a time of low alkaloid accumulation. No activity was found in the root sap of 9-week-old plants or in the sap from stems or leaves. The pH optimum was between 5.0 and 5.8, and the reaction was inhibited by physostigmine. The extract would also hydrolyze homatropine and nova-

TABLE V CHANGESI N ALKALOIDCONTENTOF Datitra stramoniitm ROOT CULTURESI N RESPONSETO MEDIUMCONTAINING PLANTGROWTHREGULATORS~ ~

Treatment*

B5O

NK5

a

Time from subcultureC (days)

HYg

cus

Tro

Tri

ACT

DaT

PaT

Apo

Hyo

Total

0 8 14 5 8 14

0 39 0 0 0

38 66 0 0 1

15 18 5 0 0 4

110

65 370 21 1 194 98 8

20 87 131 7 4 2

-

280 29 229 9 6 2

850 800 1490 117 56 13

1380 1393 2546 340 166 29

Alkaloid content (nmolig FW)d

30 203 8 2 0

19 49 0 0 0

Data from Robins et a[. (23).

* B50 medium contained Gamborg’s B5 salts with the addition of 3% sucrose: NK5 contained, additionally, 2.0 mgiliter a-naphthaleneacetic acid and 0.2 mgi liter kinetin. The initial subculture was made with roots that were 14 days old. Hyg, Hygrine; Cus, cuscohygrine; Tro. tropinone: Tri. tropine: ACT.3-acetyltropine: DaT. 3.6-diacetyltropine: PaT, 3-phenylacetyltropine; Apo, apohyoscyamine; Hyo, hyoscyamine. The total includes some further minor alkaloids.

2.


I67

tropine, although cocaine was not attacked. Esterase activity and its possible relationship with hyoscyamine synthesis were also studied by Kaczkowski (127; see Section VI1,B). Cosson and Paris (152) estimated hyoscyamine and scopolamine esterase activity in extracts made from the roots and aerial parts of Datura tatula plants at various stages of development. They found that root extracts generally gave a higher level of activity, whereas in extracts of aerial parts the greatest activity could be demonstrated prior to flowering; during fruiting, the activity disappeared from the aerial organs but persisted in the roots. The activity of atropine esterase in intact roots and cultured roots of various solanaceous tropane alkaloid-producing species has recently been thoroughly documented by Kitamura and colleagues (153). Appreciable levels of activity were found in roots of plants of Darura farufa,Hyoscyamus niger, Atropa belladonna, Scopolia japonica, and Duboisia leichhardtii. The highest activities were found in roots taken from fruiting plants of D.tatula and H . niger; roots taken from growing plants of these species in full leaf, or from flowering plants, gave activities of around 15% of these values. Roots from plants of A . belladonna, whether growing, flowering, or fruiting, gave broadly similar values intermediate between these limits. In no case were measurable activities found in the leaves or stems of plants. Furthermore, in contrast to the activities found in normal plant roots, no activity was detected in cultured roots of these species, despite the presence of substantial accumulations of alkaloids. It appears that the presence of stems and leaves is essential for the development of atropine esterase activity, suggesting that the function of the enzyme may be the hydrolysis of alkaloid transported from the aerial parts back to the roots. In support of this, atropine esterase in regenerated plantlets of Duboisia myoporoides was initially very low in relation to that of seedlings and appeared to be correlated with a very low alkaloid concentration in the leaves of the plantlets (154). The picture that emerges, therefore, is one in which the roots are likely to be the chief sites of both alkaloid synthesis and degradation, with alkaloids being transported to and from the aerial parts as required in response to developmental or other factors (see Section X). At present, however, the metabolic fate of the basic and acidic fragments of hydrolysis remains largely uninvestigated. It would appear that, to some extent, they are reutilized for alkaloid biosynthesis. When littorine containing I4Clabel in the acidic moiety and 3Hlabel in the alkamine moiety was fed to Datura innoxia plants, both isotopes became incorporated into hyoscyamine (102). The initial ratio of 3H to I4C was not maintained,

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RICHARD J. ROBINS A N D NICHOLAS J . W A L T O N

however, indicating deesterification of the littorine followed by the differential utilization of the two resulting fragments. A number of tropane alkaloid-producing genera form small quantities of nor-type alkaloids in which the nitrogen atom is unmethylated (59). In principle, these compounds could be produced directly from putrescine, via pyrroline, without methylation (see Section IV,A). Alternatively, however, they might be produced by demethylation of the methylated alkaloids (e.g., norhyoscyamine from hyoscyamine), by analogy with the formation of nornicotine from nicotine, shown to occur in leaf extracts of Nicotiana species (155,156). Evidence on this possibility is presently lacking. Either way, however, these compounds can hardly be regarded as degradation products, and, furthermore, it is doubtful whether they are any more susceptible to extensive degradation than their methylated counterparts. A quite general reaction of alkaloids is N-oxidation. Phillipson and Handa (157) isolated the two isomeric N-oxides of hyoscyamine from species of Atropa, Datura, Hyoscyamus, Scopolia, and Mandragora and one N-oxide of hyoscine from species of the first four genera. Substantial amounts of the hyoscyamine N-oxides were present in A. belladonna (between 5 and 40% of the amount of tertiary base), with particularly large quantities being present in the seeds of mature fruits. In view of the insolubility of the N-oxides in diethyl ether, it is possible for their occurrence to be overlooked in routine alkaloid extraction procedures. Nothing is known, however, of the further metabolism of these compounds, or whether they represent end products more or less stable than the tertiary bases from which they are derived. Interestingly, in Senecio vulgaris root cultures, the major stable end product accumulated is senecionine Noxide (158). Furthermore, it appears that it is in this form that the alkaloid is translocated in the plant (41).

X. Overall Regulation of Pathway Alkaloid biosynthesis is regulated, indeed made possible, by organizational features at the cellular and tissue levels that ensure that an ordered sequence of reactions occurs and that appropriate relationships are maintained with other metabolic processes. In contrast, at the level of the whole organism, alkaloid production is affected and regulated by a wide range of nutritional and environmental factors. The mechanisms relating such influences at the whole-plant level with their consequences at the biochemical level are the province of both physiologists and molecular

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169

biologists and pose problems that are particularly difficult to identify and to solve. AT BIOCHEMICAL LEVEL A. REGULATION

With the exception of hyoscyamine 6P-hydroxylase (and its associated activities), which is known in roots to be present specifically in the pericycle (143; see Section VIII,A), no information is yet available on the tissue or subcellular localization of enzymes of tropane alkaloid biosynthesis. Progress on both of these questions needs to be made before a full understanding of the organization of the pathway can be achieved. As a result of recent investigations, however, insights into the biochemical regulation of the pathway are beginning to emerge. Simple feeding experiments with metabolites of the pathway supplied to transformed root cultures of Datura species have indicated likely limiting steps in hyoscyamine formation. Feeding individually putrescine, agmatine, Nmethylputrescine, tropinone, or tropine to root cultures of D . stramonium was, in each case, largely ineffective in increasing hyoscyamine formation (Table VI) (21). On the other hand, substantial increases in the production of hygrine, cuscohygrine, tropine, and 3-acetyltropine were found after feeding the amine precursors, as well as increases in tropine and 3acetyltropine after supplying tropinone; tropine was also metabolized to 3-acetyltropine (Table VI). Broadly consistent data from cultures of the D. candida X D . aurea hybrid have also been obtained (22). Of special interest is the observation that exogenous tropinone was entirely converted to tropine and 3-acetyltropine virtually without stimulating the production of hyoscyamine. Even when fed at 5 mM, tropinone is totally reduced within 48 hr. This suggests that the reduction of tropinone is rapid in relation to hyoscyamine formation and unlikely to be of regulatory significance. This conclusion is further supported by the presence of substantial tropinone reductase activities in transformed root cultures of both D. stramonium (82,87) and the D . candidu X D . aurea hybrid (22; see Section V). It may also be inferred from Table V1 that the formation of 3-acetyltropine occurs in response to a surfeit of tropine. Its seemingly adventitious formation may thus bear little direct relationship to the mechanism of hyoscyamine formation (see Section VII). This interpretation is also consistent with the effect of feeding TBON, which is metabolized to the 3-O-acetyl derivative of the corresponding alcohol, TBOL (see Scheme 9) (92). From these results it might be deduced that the supply of tropic acid is likely to be an important limitation to hyoscyamine production. This has been tested in a number of systems by feeding free tropic acid

TABLE VI EFFECTS OF FEEDING TROPINE A N D METABOLIC PRECURSORS ON INTRACELLULAR ALKALOID LEVELS I N TRANSFORMED ROOT CULTURES OF Datura stramoniuma

Alkaloid content (nmol/g FW)c Experiment I

Compound suppliedb None Putrescine Agmatine

2

None N-Methylputrescine Tropinone Tropine

a

Concentration (mM)

Growth (g FW)

Hyg

Cus

Tro

Tri

ACT

DaT

Apo

Hyo

1 .O 5.0 1.o 5.0 1 .O 5.0 1 .O 5.0 1.o 5.0

6.7 7.4 7.1 7.8 6.8 9.5 8.2 9.0 9.2 9.5 10.1 12.2

7 58 98 28 89 7.8 98.5 88.5 6.6 2.8 7.6 10.4

9 6 278 83 344 10.6 306.7 237.6 5.6 14.2 7.1 20.7

ndd nd nd nd nd 4.5 9.8 7.1 5.9 5.9 2.8 4.3

150 520 775 357 504 65 46 1 290 213 1469 592 1322

90 289 419 34 1 49 1 82 33 1 235 254 1425 460 78 1

nd nd nd nd nd 66 I07 74 65 90 65 91

278 443 157 265 128 218 137 106 260 181 162 154

1205 1314 1271 1472 670 1734 1721 1906 1698 2019 2034 2039

Data from Robins ef a / . ( 2 1 ) . Additions of compounds were made to roots at subculture, and alkaloids were determined 21 days later. Hyg, Hygrine; Cus. cuscohygrine; Tro, tropinone; Tri, tropine. ACT. 3-acetyltropine; DaT. 3,6-diacetyltropine; Apo, apohyoscyamine; Hyo, hyoscyamine. nd, Not determined.

2.


171

(21,22,123,159,160). The effect has been variable, but, in the main, no

enhanced tropoyltropane levels were obtained. This could simply indicate that a further step is limiting, for example, the activation of tropic acid. In some instances tropic acid was detrimental to hyoscyamine production. For example, when fed at 1-2 mM to root cultures of D. stramonium, exogenous (RS)-tropic acid caused a 60% reduction in hyoscyamine accumulation. In contrast, 1-2 mM (RS)-phenyllactic acid (while also failing to stimulate hyoscyamine production) did not have the same inhibitory effect (21,f13). (RS)-Phenyllactic acid did, however, enhance the formation of littorine, causing a change in the littorine to hyoscyamine ratio from 0.07: 1 to 0.26: 1 when fed at 1.5 mM (113). The implication of these experiments, namely, that free tropic acid is acting indirectly on the formation of hyoscyamine, is strengthened by recent feeding experiments. Root cultures of Duboisia leichhardtii incorporated ~ ~ - [ l - ' ~ C ] t r o acid p i c into hyoscyamine very poorly (97 : 3) resulting from the chelation control operating between the lithium cation and the free amine. Cyclization of the allene 212 with p-toluenesulfonic acid, followed by hydrolysis of the resulting bicyclic enol ether 213, gave the 7-indolizidinone 209. Aldol condensation of 209 with aldehyde 214 followed by dehydration afforded the enone 215. Stereoselective reduction of 215, followed by silylation of the resulting allylic alcohol, provided the indolizidine 216. Debenzylation of 216 followed by Swern oxidation furnished the aldehyde 217, the coupling of which with the known ylide 218 provided the a’-silyloxylated (E)-enone219. Threo-selective reduction of 219 with LiAIH, was accompanied by desilylation to afford (+)-allopumiliotoxin 339B [( +)-831 (Scheme 26). Trost and Scanlan reported a novel synthesis of ( +)-allopumiliotoxin 339 B [( + )-831 using an innovative, Pd(0)-catalyzed 6-endo-trigonal mode of cyclization of the vinyl epoxide 224 (78). Thus, the treatment of the Lproline-derived ketone 211 with the allyltitanium reagent 221, followed by epoxidation, afforded 220, which was diastereofacially cyclized with Pd(0) to provide the indolizidine 223 as a single isomer. Hydroxyl groupdirected epoxidation of 223 gave the vinyl epoxide 224, which, under Pd(0)-induced condensation with the ally1 sulfone 225, provided the glycol 226 possessing the side chain profile of the target alkaloid. Desulfonylation of 226 and subsequent threo-selective reduction, accompanied by concomitant desilylation, gave ( + )-allopumilitoxin 339B [( +)-831 (Scheme 27). The first total synthesis of ( + )-allopumiliotoxin 339A [( + )-82], an indolizidinediol containing a @-oriented C-7 hydroxyl, was achieved via the pivotal, nucleophile-promoted iminium ion-alkyne cyclization step by Overman et ul. (48). Alkyne 227, provided with the full side chain profile of the pumiliotoxin A alkaloids (77, 82, and 83), was prepared from (R)2-methyl-4-pentenol (228) in eight steps. Addition of the lithio derivative of 227 to the a-benzyloxyaldehyde 229 provided the alcohols 230 and 231 with 4 : I selectivity. Treatment of 230 with silver triflate afforded the pyrrolidino-oxazine 232, the precursor for the key cyclization step. Iodinepromoted cyclization of 232 provided the alkylidene-indolizidine 233, with no other stereoisomer. Deiodination of 233, followed by debenzylation afforded ( + )-allopumiliotoxin 339A [( +)-82] (Scheme 28). Both the Overman and Trost groups have used various strategies based on (S)-proline for the synthesis of the indolizidine skeleton. Gallagher has reported the enantioselective synthesis of pumiliotoxin 25 ID (78) employing an allene-based electrophile-mediated cyclization and the rapid

218

HIROKI TAKAHATA A N D TAKEFUMI MOMOSE

210

21 1

21 2

e-g

d

3

213

209

21 5

CH3 21 4

-

I

h,i

"OTDMS

"OTDMS

216

21 7 218

21 9

(+)-a3

(+)-79

SCHEME 26. Reagents: a , CF3C02H;b, 1-lithio-1-methoxyallene; c, TsOH; d, HCI; e, Ph3CLi;f, 214; g, (CF3C0)2,DBU; h, NaBH4, CeC13;i, TBDMSCI, n-BuLi; j, Na, NH3; k, (COCI),, DMSO, EtjN; I, 218; m, LiAIH4.

elaboration of the indolizidine skeleton by the correct choice of an electrophilic trigger (79). Pd( 11)-mediatedcyclization of the enantiomerically pure allenic arnine 234 provided the 2-substituted pyrrolidines 235a,b with a negligible level of diastereoselectivity (1 : 1). Reduction of 235a to the corresponding allylic alcohol, followed by Claisen rearrangement, effected homologation to the ester 236. Hydrolysis of 236 and reaction of the resulting carboxylate salt with acetic anhydride led directly to the bicyclic lactam 237 as a single enantiomer. Hydration (hydroxymercuratiod reduction) of 237 provided the tertiary alcohol 238 with a high level of stereoselectivity (10: 1) in favor of the expected axial alcohol. The introduc-

3.

219

SIMPLE INDOLIZIDINE ALKALOIDS

+ a __c

SCzH,

-

222 21 1

220

('PrOkTi -SC,H,

221

-

-

C

223

224

0 225

226

(+)-83

SCHEME27. Reagents: a, 221, (CF3CO),0; b, (CH3),0BF4, NaOH; c , catalytic (dba)3Pdz-CHC13,(RO),P, H,O; d, CF3C03H;e , 225, (dba)3Pd2-CHC13,dppf, H,O; f. Na(Hg), NaHPO,; g, LiAIH4.

CN

b

230, R'= OH, R2= H 231, R'=

232

H,R ~ OH = CHI OH CH3,,.& OH

d.e

r

233, R= En, X=l (+)-82.R= X=H

SCHEME28. Reagents: a, 227, "BuLi; b, AgOS02CF3;c, TsOH, NaI, (CH,O),, acetone-H20; d, "BuLi, MeOH; e , Li, NH3.

220

HIROKI TAKAHATA A N D TAKEFWMI MOMOSE

tion of the (Z)-alkylidene unit at C-6 was performed by an aldol condensation of 238 with (R)-2-methylhexanal followed by syn elimination and anti elimination of the resulting alcohols 239a and 239bc,respectively. Finally, 1,2-reduction of the unsaturated lactam moiety of the (Z)-alkylidene indolizidine (Z)-240 thus obtained was achieved by using LiAICI, to afford pumiliotoxin 251D [( +)-781 (Scheme 29). Honda et al. reported a 16-step synthesis of the key intermediate 237 from the product (R)-241 of the Katsuki-Sharpless kinetic resolution of the racemic 2-furylmethanol 241, derived from 2-lithiofuran and 5-trimethylsilyl-4-pentynal (80).

d,e

b,c PhACH3

235a

234

236

235b, epimer at C-2

on

OH

OH

f.g '0 1.1.

237 I

1

239a,b,c

(0-240

16steps

li

TMS

(R)-241

EH,

(+)-78

EH3

(2)-240

SCHEME 29. Reagents: a, 1% PdCl,, CO, CH30H, CuCI,; b, DIBALH; c, (EtO),CCH,, H + ;d, NaOH; e, (CH,CO),O; f, Hg(02CCH3)2;g, NaBH,, NaOH; h, LDA, (R)-2-methylhexarial; i, DCC, Cu(I)Cl;j, CH3S02C1, pyridine, KOH ( E : Z = 2.6: 1); k, LiAIH,-AICI,; I, Ref. (80).

3.


22 1

111. Elueoculpus Alkaloids

Following the discovery (81) of the Elaeocarpus alkaloids, several total syntheses concerning racemic elaeokanines were reported (82). However, the absolute configuration of these alkaloids remained unknown. The first asymmetric total synthesis of elaeokanines A (242) and B (243) via an optically active a-sulfinylketimine (244) was achieved by Hua et af.,which permitted the absolute stereochemistry of these alkaloids to be established (83). (+)-(R)-Sulfinylketimine 246, prepared by reaction of the anion of pyrroline 245 with (-)- 1-menthyl p-toluenesulfinate, was alkylated with 1,3-diiodopropane to provide the key bicyclic intermediate 244. Reduction of 244 with NaBH, gave the four separable diastereomeric indolizidines 247a,b and 248a,b in the ratio 4 : 4 : 1 : 1 . The stereochemistry at C-8a of the sulfoxides was determined by desulfurization of each isomer, which gave either a (-)-indolizidine or a ( )-indolizidine. a-Hydroxybutylation of the major isomer 247a or 24713 furnished a mixture of the alcohols 249a and 24913 in a 2 : 1 ratio, whereas the similar reaction of each minor isomer 248a,b provided a 2 : 1 mixture of 250a,b. Single-crystal X-ray analysis of 249a established the relative stereochemistry. Dehydrosulfinylation of 249a or 249b furnished the natural enantiomer (-)-elaeokanine B [( -)2431, which was oxidized to afford the unnatural antipode (-)-elaeokanine A [(-)-2421. Under the same reaction conditions, dehydrosulfinylation of 250a,b provided (+)-251, which was oxidized to afford the natural enantiomer (+)-elaeokanine A [( +)-2421 (Scheme 30). Comins and Hong reported the asymmetric total synthesis of elaeokanine C (2521, together with that of elaeokanine A (242), using a chiral dihydropyridone intermediate (84). Reaction of the chiral l-acylpyridinium salt 253, prepared from 4-menthoxy-3-(triisopropylsilyl)pyridine(85) and the chloroformate of (-)-8-(4-phenoxyphenyl)menthol,with the Grignard reagent 254 gave the alcohol 255 in 92% diastereomeric excess, which was converted to the chloride 256 by treatment with triphenylphosphine and N-chlorosuccinimide (NCS). On removal of the chiral auxiliary with sodium methoxide, concomitant cyclization occurred to afford the enone 257. Carbamylation of 257 followed by desilylation yielded the amide 258. Stereoselective reduction of the enaminone moiety of 258 using catalytic hydrogenation over PtO, gave a mixture of alcohols 259a,b in a 95 :5 ratio. Treatment of 259a with cerium chloride and n-propylmagnesium chloride gave elaeokanine C [( +)-2521. Because the optical rotation for the isolated natural (-)-elaeokanine C is levorotatory, it was demonstrated that the absolute configuration is (7R,8S,8aS). Elaeokanine C was converted to

+

222

HIROKI T A K A H A T A A N D T A K E F U M I MOMOSE

U 245

246

d

247a,b

244

G!J;+< 249a

+

e l (-)-243

(-)-242

249b

248a,b

250a

(+)-251

(+)-242

250b

SCHEME 30. Reagents: a, LDA, (-)-(S)-I-menthylp-toluenesulfinate;b, LDA, 1,3-diiodoPropane; c, NaBH,; d, LDA, butyraldehyde; e, toluene; f, pyridinium chlorochromate.

+ )-elaeokanine A [( + )-2421 by treatment with sodium hydroxide (Scheme 31). The asymmetric synthesis of elaeokanines A and C based on a novel approach involving diastereoselective addition of an enolic nucleophile to a tricyclo-iminium species, and subsequent removal of the stereo template by a retro-Diels-Alder reaction, was achieved by Koizumi and co-workers (86). Oxidation of the maleimide 260, prepared by the addition of 10mercapto-isoborneol to N-tert-butyldimethylsilyl (N-TBDMS) maleimide followed by chlorination and dehydrochlorination, afforded the sulfinylmaleimide 259 as a single diastereomer. Diels-Alder reaction of 259 with cyclopentadiene produced the em-sulfinyl adduct 262 with greater than 99% diastereomeric excess (87). Desilylation of 262 and subsequent N alkylation gave the acetal 263. Regioselective reduction of 263 followed by desulfinylation with samarium( 11) diiodide afforded the y-hydroxylactam 264, which was transformed into 265. Addition of 2-(trimethylsilyloxy)pent-I-ene to 265 in the presence of BF,-Et,O provided the lactam 266 as a single diastereomer possessing a p-oriented five-carbon chain at

(

3.

258


259a, R'= OH, R2=H

223

(+)-252

259b. A'= H. R2= OH

SCHEME 31. Reagents: a. 254; b, H,O+ ;c , Ph,P, NCS; d, NaOMe; e, LDA, dirnethylcarbamoyl chloride; f, (COOH),; g, HI, PtO,; h, PrMgCI, CeCI,; i. NaOH.

C-5. Acid-catalyzed aldol reaction of 266 afforded the tetracyclic lactam 267, which was converted to the dehydroindolizidinone 268a,b, separable diastereomers at C-8a, in a 3 : 1 ratio by flash vacuum pyrolysis (retroDiels-Alder). Hydrogenation of the major isomer 268a and subsequent protection of the ketone produced the lactam 269. Reduction of 269 followed by acid hydrolysis gave elaeokanine C [( +)-2521, which was transformed into elaeokanine A [( + 1-2421 according to the same procedure as described in Scheme 31 (Scheme 3 2 ) .

IV. Slaframine Forage materials contaminated with fungus Rhizocronia legitminicola (88) are responsible for a disease in ruminants known as black patch (89). The most obvious symptom associated with ingestion of contaminated feed is excessive salivation, which is thought to be caused by the alkaloid slaframine (270). Slaframine has previously been mentioned on several occasions in this treatise. The chapter by Howards and Michael offered a comprehensive review, covering the isolation, structure, biosynthesis, synthesis, and biological activity of this alkaloid ( I ) . Thereafter, further biological studies on slaframine included a potentially important use of the alkaloid in deliberately altering ruminal fermentation to improve the efficiency of feed utilization, lactation, and growth in sheep and cattle, and the ability of slaframine to stimulate circulating concentrations of a

224

HIROKI TA K A H A T A AND T A K E F U M I MOMOSE

259

260

c,d

-

262. R= TBDMS 263, R=

I

h

'

264, R= H c265,

266

R=Me

268a,b

qo]

267

269

(+)-252

SCHEME32. Reagents: a, 3-chloroperbenzoic acid; b, cyclopentadiene, ZnCI,; NaH; e , NaBH,; f, Sm(II)12;g, pyridinium c, silica gel; d, 2-(2-bromoethyl)-l,3-dioxolane, p-toluenesulfonate; h. 2-(trimethylsilyloxy)pent-I-ene, BF,-Et,O; i. conc. HCI; j , flash vacuum pyrolysis; k, H,, Pt on alumina: I , (EtO),CH, TsOH; m, LiAlH.,; n, 10% H2S04: 0, NaOH.

growth hormone in broiler chicks was also investigated (10). Biosynthetic studies by Harris et d.have been actively pursued (90). Recently, the asymmetric synthesis of (-)-slaframine has been achieved by three groups. Pearson et ul. reported the first synthesis of (-)-270 via reductive cyclization of an epoxy azide as a key step (Scheme 3 3 ) (91). N-Benzylation of L-glutamic acid, followed by protection, provided the N benzyloxycarbonyl derivative 271. Diborane reduction of both carboxyls afforded the diol 272, which was selectively silylated to produce 273, presumably because of the different steric and electronic environments of the two hydroxyl groups. Conversion of 273 to the azide 274 was accomplished with the Mitsunobu reaction. Deprotection of 274 and oxidation of the resultant hydroxyl at C-4 gave the azido aldehyde 275, which was converted to the Z-alkene 276 by a highly stereoselective Wittig olefination. Epoxidation of 276 with m-chloroperbenzoic acid (MCPBA) was nonselective, producing a 1 : 1 ratio of the diastereomeric epoxides 277 and 278. Tosylation of 277 afforded the azide 279, and selective reduction of 279 to an amine in the presence of the two benzyl protecting

3.

S I M P LE I N D O L I Z I D I N E ALKALOIDS

'

27 1

272, X=CHpOH, Y= OH

225

276

273, X=CH20TBDMS, Y= OH

d'e

c

274. X=CH,OTBDMS, Y= N3

275. X=CHO, N3

278 R= H i

283 R=Ts '

c

285 R,= En, R2= Cbz, R3= Ac 286 R,= H, R2= H, R= , A

SCHEME 33. Reagents: a, BH,-THF; b, TBDMSCI. pyridine. catalytic DMAP: c. Ph3P, DEAD. (PhO),P(O)N,; d , "BudNF; e . (COCI)?. DMSO, NEt3; f. Ph3P+ (CH2),0HBr-, KN(SiMe,),. TMSCI. 275; g. HCI; h, MCPBA; i. TsCI, pyridine. catalytic DMAP; j , 10% Pd/C ( 5 wt %), H?; k, K2C03;I, Ac,O, pyridine: m, 10% Pd/C (100 wt %, 10 mol 7% Pd). H,;n, Ac,O, pyridine.

groups was accomplished by hydrogenolysis. The resultant amine was not isolated, but was directly heated in the presence of a base. Intramolecular epoxide opening and subsequent alkylation of the nitrogen by the tosylate afforded the indolizidine 280. Acetylation of the secondary alcohol in 280

226


gave 281, which was deprotected to afford (-)-slaframine [( -)-2701. The signs of the specific rotations of both synthetic N-acetylslaframine 282 [a];' -11.2' (EtOH) and natural 282 [ a ] $ -15.9" (EtOH) are the same, indicating that the absolute stereochemistry of natural ( 4 - 2 7 0 is (lS,6S,8aS). A similar sequence afforded (-)-I ,8a-diepislaframine 286 in good yield from the epoxy tosylate 283 (Scheme 33). Cha and co-workers reported an enantioselective synthesis of ( 3 - 2 7 0 through an intramolecular azide [2 + 31 dipolar cycloaddition reaction (Scheme 34) (92). The chiral phosphonium salt 287 was prepared from the readily available aldehyde 288 (obtained from L-aspartic acid in eight steps) (93). Diisobutylaluminum hydride (DIBAL) reduction of the known and readily available lactone 290 (94) and subsequent Wittig reaction with the ylide derived from 287 afforded the adduct 291. Subsequent tosylation followed by DIBAL reduction yielded the alcohol 292. Selective N-tosylation of 292 followed by azidation with sodium azide via an intramolecular azide [2 + 31 cycloaddition produced the imine 293. Bicyclic ring closure was achieved uneventfully by selective 0-mesylation and subsequent NaBH, reduction to produce the protected slaframine 294. Finally, a series of straightforward deprotection steps and 0-acetylation afforded (-)slaframine [( -)-2701. The synthesis of (-)-270 was executed in 11 steps via radical cyclization from resolved (S)-3-hydroxy-4-pentenamide (295) by Knapp and Gibson

OA N A

a-c

kN, PMB

PMP

PMP

R

c288

g-i

- Hbo \

2pso\ e.f

OTs

290

291

OH

292

R= CHo

L289

R= CH2Br 287 R= CHZ'PPh3Bi

293

PMP= pmethoxyphenyl PM0= pmethoxybenzyl

294

(-)-270

SCHEME34. Reagents: a, NaBH,; b, TsCI, catalytic DMAP; c, LiBr, NaHCO,; d, PPh,; e, KN(SiMe,h; f, 290, DIBAL; g, N-tosyl-N-methylpyrlidine perchlorate; h, NaN,; i, toluene; j, MsCI, Et3N; k, K2C03;I, ceric ammonium nitrate; m, "Bu,NF; n, Na, NH,; 0,HCI, AcOH.

3.


296

295

300a a-isomer R= THP

2917

302

?A'

227

299

303

300b p-isomer R= THP 301a a-isomer R= H 301b D-isomer R=H

WN3 - PN"' 0

AcO

ti

304

AcO

(-)-270

35. Reagents: a, TMSOTf, Et3N: b, 12; c, aq. Na2SOl: d. PhSeSePh, NaBH4; e, TBDMSCI, irnidazole: f, NaH, 298: g, "Bu4NF;h, AczO, pyridine: i, (Me$i),SiH, AlBN: j, AcOH; k, MsCI, 'PrzEtN; I, NaN3; rn, BH3-SMe2: n, TMDEA; 0,H2 5% Pd/C. SCHEME

(95) (Scheme 35). Stereoselective iodolactamization of 295 provided the

iodolactam 296 (96). Replacement of the iodo in 296 with the phenylseleno group and subsequent protection of the hydroxyl in 296 afforded 297. N Alkylation of 297 with 3-iodo-2-(2-tetrahydropyranyloxy)propene (298) and subsequent replacement of the silyl group and installation of the acetyl group gave the required substrate 299. Formation of an indolizinone from 299 by radical-initiated cyclization using tris(trimethylsi1yl)silane proceeded to yield two pairs of diastereomers 300a,b in the ratio 7 : I owing to the tetrahydropyranyl (THP) group. Hydrolysis of the 6a-hydroxyl diastereomer (300a) provided a single alcohol (301a). Conversion of 301a to its methanesulfonate 302 followed by SN2 displacement of the mesylate with azide gave the azidoindolizidinone 303. Reduction of the lactam with a borane-dimethyl sulfide complex and liberation of the free amine with tetramethylenediamine afforded the indolizidine 304. Finally, azidoslaframine (304) was converted to (-)-slaframine [( -)-2701 by catalytic hydrogenation.

228

H l R O K I T A K A H A T A A N D T A K E F U M I MOMOSE

H OH

305

H

OH

9H

306

OH

307

308

31 0

309

FIG.8.

V. Hydroxylated Indolizidines The alkaloids to be considered in this section are the l-hydroxyindolizidines 305 and 306, indolizidinediols 307 and 308, swainsonine (309), castanospermine (310), and their analogs (Fig. 8). A. ~-HYDROXYINDOLIZIDINES A N D I ,2-DIHYDROXYINDOLlZlDlNES

(IS,8aS)-l-Hydroxyindolizidine(305) and (IR,8aS)-l-hydroxyindolizidine (306) were recognized as key precursors for the biosynthesis of the toxic indolizidine alkaloids slaframine (270) and swainsonine (309), respectively, in the fungus Rhizoctonici lc~griminic~olrr. Investigation of their elegant biosynthesis has been performed by Harris et al. (90), and the current view of their biosynthesis in R . iegrrtninicola is summarized in Scheme 36. It was shown that the alkaloids are formed from L-lysine via L-pipecolic acid, 1 -oxoindolizidine 310, and 1 -hydroxyindolizidines 305 and 306. Harris and Harris prepared the four diastereomers of l-hydroxyindolizidine (305,306,312, and 313) in high optical purity (>%%I by NaBH, reduction of the ( + )- and (-)-3-bromocamphor-8-sulfonic acid (BCS) salts of I-oxoindolizidine [( ?)-311], followed by separation of the resulting diastereomeric alcohols with ion-exchange chromatography (Scheme 37) (97). Enantiocontrolled synthesis of 305 has been achieved through a condensation of (3R,2S)-hydroxyprolinal (314) with a three-carbon synthon by Sibi and Christensen (98). Baker's yeast reduction of the protected 3ketoproline ester 315 afforded 3-hydroxyproline ester 316. Interchange of the benzyloxycarbonyl with the tert-butoxycarbonyl protecting group, followed by protection of the hydroxyl group and conversion of the ester to the aldehyde using DIBAL reduction, provided the aldehyde 314. Wittig

3.


L-lysine

-eH L-pipecolic acid

305

u

229

OH

306

310

H

307

OAC

270

309

SCHEME36. Biosynthesis of slaframine and swainsonine

reaction of 314 with the phosphorane 317 gave a mixture of cis- and trcinsolefins 318. Hydrogenation of 318 followed by mesylation furnished the mesylate 319, which was treated with 3M HCl to provide the desired (IS,8aS)-1-hydroxyindolizidine (305) (Scheme 3 8 ) . An asymmetric synthesis of 1-hydroxyindolizidines 305 and 306 was performed by a short reaction sequence involving intramolecular amidomercuration as shown in Scheme 39 (99). The kinetic resolution and asymmetric epoxidation of racemic N-benzyloxycarbonyl-3-hydroxy-4-

7 (f)-311

(+)-BCS salt

\

306

(-)-BCS salt

313

SCHEME37. Reagents: a, ( + ) - B C S ; b, (-)-BCS; c, NaBH,; d, Dowex 50.

230


,.,OH

-2-

,OTBDMS

b-e

q..cmE,

f Q'CHO

b

Ph3P'(CH*),OHCI-

Cbz

Cbz

Boc

31 5

31 6

31 4 317

p

s

g,h

(3 Boc

BOC

OH

OMS

31 8

i

-

305

31 9

SCHEME38. Reagents: a, baker's yeast; b, H,, Pd; c , BoczO; d, TBDMSCI, base; e , DIBAL; f, 317, LiHMDS; g, H2, Pd; h, MsCI, Et,N; i , 3 M HCI.

pentenylamine (320), capitalizing on the Katsuki-Sharpless reagent, provided three kinds of products, (S)-320, the epoxy alcohol 321, and the pyrrolidine 322 (100). Stereoselective intramolecular amidomercuration of (S)-320 followed by radical Michael addition to methyl acrylate afforded the cis-2,3-disubstituted pyrrolidine 323 without isolation of the trans isomer. Exposure of 323 to hydrogenation gave the indolizidinone 324, which on reduction with LiAlH, provided 305. Conversion of 324 to 306

c-c Y"

Cbz

(+)-320

a

/

+c

KY+--$ YH I

Cbz

(S)-320

Cbz

321

OH

Cbz

322

If ! T

OCOPh

p : ( y J 0

325

kj OH

306

SCHEME39. Reagents: a, D-(-)-diisopropyl tartrate, 'BuOOH, Ti(O'Pr),; b, Hg(O COCFh; c , CHz=CHCOOMe, NaBH(OMe),; d , H,, Pd(OH),; e, LiAIH,; f, Ph3P,diethy1 azodicarboxylate, PhCOOH.

,

3.

23 1


was achieved by inversion of the hydroxyl group in 324 employing the Mitsunobu reaction followed by reduction. Indolizidinediol307 has been isolated from R. legurninicola and Astuagalus lentignosus (101). In addition, 307 has been demonstrated to be a biosynthetic precursor of swainsonine (309) as shown in Scheme 36 (90). The absolute configuration of (1S,2R,8aS) was confirmed by efficient reutilization of the compound in the further biosynthesis of swainsonine. Lentiginosine (308), isolated from A . lentignosus, inhibited the a-glycosidase amyloglucosidase (102). The structure was confirmed by spectroscopic data. On the basis of biosynthetic considerations, the absolute configuration is assumed to be (IS,2S,8aS). Heitz and Overman reported the enantiodivergent synthesis of both enantiomers of 1,2-indolizidinedioI (307) from the common intermediate 326, which was prepared in three steps from commercially available Disoascorbic acid (Scheme 40) (103).The enantiodifferentiation stems from cyclization at either the carbon site represented by the carbonyl or the one

X c-e

three steps

D-isoascorbic acid

326

327

328

330

329

(-)-307

0 x 0

TMS

332

(+)-307

331

SCHEME 40. Reagents: a, MsCI, Et3N;b, NaH; c, Lawesson reagent; d, Et,0BF4, 2.6di-rerr-butylpyridine; e , LiBEt3H; f , Cu(OS0,CF3),; g, H2. PdlC; h, 2M HCI; i, S03-py, DMSO; j, Ac,O, DMAP; k, BF,-OEt2; I, LiAIH4.

232

H l R O K l T A K A H A T A A N D T A K E F U M I MOMOSE

bearing the hydroxymethyl in the amide 326. The lactam 327, a potential precursor to an iminium ion intermediate, was obtained from 326 by conversion via mesylation followed by cyclization. The conversion of 327 to the 2-ethylthiopyrrolidine 328 was performed by a sequence involving thioamidation, methylation, and reduction. The iminium ion-vinylsilane cyclization was accomplished by treatment of 328 with copper triflate to provide the tetrahydroindolizidine 329, which was transformed by reduction followed by deprotection of the resulting acetonide 330 into the desired (-)-307, [a];' -39.4' (0.58, CHCI,). On the other hand, the conversion of 326 to the acetate 331 was carried out by oxidation of the hydroxymethyl followed by acetylation of the resulting hydroxy lactam. The acetoxy lactam 331, on treatment with boron trifluoride. underwent cyclization on the less hindered convex face to give 332, which was converted by the standard transformation to the unnatural ( 1-307 [a];4 +40.2" (0.88, CHCI,). An enantiocontrolled synthesis of the acetonide form (330) of (-1-307 was achieved starting with the pyrrolidino ester 323, described previously (Scheme 39), by Takahata et al. (104). Reduction of 323 followed by selective monotritylation provided the 3-hydroxypyrrolidine 333. Elimination of the hydroxyl group in 333 afforded the 3-pyrroline 334, which was dihydroxylated from the opposite side to the ring appendage at C-2 to furnish the diol335 as a single diastereomer. Subsequent acid hydrolysis. acetonide formation, mesylation, and cyclization afforded the desired 330 (Scheme 41).

+

,+OH Q..,,-Co0Me Cbz

323

335

ab

+OH

1Q.Cbz "

f l M O T r

333

336

Cbz

334

330

SCHEME 41. Reagents: a, DIBAL; b, 'HCI, Et,N; c , NaH, CS2, Mel; d , 170°C; e, catalytic OsO,, N-methylmorpholine oxide; f, HCI; g, (CH3)2C(OCH3)2. TsOH; h, MsCI. pyridine; i , H2, Pd(OH),; j. aq. K2C0,.

3.

233

SIMPLE I N D O L I Z I D I N E A L K A L O I D S

B . SWAINSONINE From the fungus Rhizoctonici legrrrninic~olciwas isolated the toxic indolizidine alkaloid swainsonine (309) (105). Swainsonine has also been shown to be present in locoweed (Astrrrgcrlus lentiginosus)(106) and Sirwinsoniu canescens (107), as well as in the fungus Metarrhizium unisopliue (108). The pronounced a-mannosidase inhibitory (109) and immunoregulative properties (110) of swainsonine have stimulated considerable chemical, biosynthetic, and pharmacological interest (111 1, and its total synthesis by several groups, including five enantioselective syntheses ( 112-1 161, has already been described ( I ) . Most of the syntheses are based on a route from carbohydrates. Hashimoto and co-workers carried out a short, enantiospecific synthesis of (-) swainsonine [(-)-3091 from D-mannose using. a5 a key step, the double cyclization of the epoxy amino ester337 (Scheme 42) ( 1 17).Conversion of the oxime 338, readily accessible from D-mannose, to the protected amine 339 was followed by selective hydrolysis to form a diol, which led to the epoxide 340. Oxidation of 340 to an aldehyde and Wittig reaction of the latter furnished the a$-unsaturated ester 341. The required 337 was obtained by reduction of 341 with sodium borohydride in the presence of trifluoroethanol as a proton source. Release of the amino group and subsequent reflux in ethanol resulted in double cyclization of 337 to the lactam 338, which was converted to (-)-309. Fleet and co-workers devised a new design in which the mannosederived azidoepoxide 343 played a pivotal role (Scheme 43) (118). The

D-mannose

NHCbz

338

341

340

339

337

NHCbz

338

(-)-309

SCHEME 42. Reagents: a , LiAIH,: b, CbzCl; c. MsCI, pyridine; d, TsOH; e, Amberlite IRA 400 resin; f, Collin’s reagent; g. Ph3P=CHC02Et; h, NaBH4. CFICH20H; i. H2. Pdi C; j , EtOH; k, LiAIH,; I, 6M HCI.

234


344

346

345

338

SCHEME43. Reagents: a, NaN,: b, camphorsulfonic acid: c, Ba(OH),; d, (CF3S02),0; e , LiCH2CO2But;f, H2, Pd/C: g, NaOMe: h, BH3-Me2S; i, CF3C02H-H20:j, ion-exchange chromatography.

dimesylate 344, readily available on a large scale from mannose, underwent selective displacement of the primary mesylate by azide anion to give the azido mesylate, which, on partial hydrolysis, afforded the diol 345. Base-mediated epoxidation of 345, followed by two-carbon extension at the terminal hydroxyl, provided the azido epoxide 343. Hydrogenation of 343 gave the pyrrolidino ester 346 by intramolecular S,2 attack of the resulting amine on the oxirane. Subsequent heating with sodium methoxide provided the same &lactam (338) as described above (Scheme 42). Preparation of the highly valuable intermediate 347 developed by Fleet and co-workers for the synthesis of (-)-swainsonine was achieved by a 15-step sequence starting from D-mannose (Scheme 44) (119). The application of selective tosylation, acetonization, and silylation to benzyl-a-Dmannoside (348) gave the tosylate 349. Nucleophilic displacement at the tosyloxymethyl in 349 by reaction with allylmagnesium chloride followed by desilylation and Swern oxidation, provided the olefinic ketone 350. Oxidation of the olefinic terminus of 350, followed by esterification of the resulting carboxyl group, furnished the ester 351. NaBH,-mediated reduction of 351 by attack of hydride from the a side and subsequent trifluoromethanesulfonation gave the triflate 352, which, on treatment with sodium azide, was transformed into the azide 353. Hydrogenation of 353 followed by lactamization gave the bicyclic lactam 354, which was converted with LiAlH, to the pivotal intermediate 347 for the synthesis of (-)-swainsonine [(-)-3091. A practical, enantioselective synthesis of (-1-309 was achieved in seven steps from 2,3-O-isopropylidene-~-erythrose (355) (120). The key step involves the construction of the bicyclic imine 358 via intramolecular 1,3dipolar cycloaddition in the olefinic azide 356 to give the triazoline 357 (Scheme 45). The requisite azide 356 was prepared in three steps (i.e., Wittig reaction of 355, tosylation, and azidation). Heating of 357 led to

3.


352

351

354

235

353

ref. 112 (-)-309 347

SCHEME 44. Reagents: a, TsCI, pyridine; b, CH,C(OCH3)2, catalytic camphorsulfonic acid (CSA); c, TMSCI, Et3N: d, allylmagnesium bromide; e, "Bu4NF; f, (COC1)2,DMSO, &N; g, NaI04, RuOZ-H~O;h, CH2N2; i, NaBH4: j, (CF3S02)20,pyridine; k, NaN,; I, H2, Pd; rn, toluene; n, LIAIH,.

361

362

SCHEME 45. Reagents: a, Br-Ph3P+(CH2),C02Et,KN(TMS),; b, TsCI, Et3N; c, NaN,; d, K2CO3; e, toluene: f , BH3; g, H202-NaOH; h, 6N HCI.

236

HlROKl TAKAHATA A N D TAKEFUMI MOMOSE

I ,3-dipolar cycloaddition to yield the cyclic imine 358 via the triazoline intermediate 357. Imino ester 358 was then hydrolyzed to afford the acid 359, which was heated to provide the enamide 361 via the spirocyclic lactone 360. A highly diastereoselective hydroboration of 361, accompanied by reduction of the lactam carbonyl, produced the swainsonine acetonide 362, which, on hydrolysis, was converted to (- 1-309. A similar route to (-)-309 was achieved by Pearson and Lin (121). Wittig reaction of 355 followed by Mitsunobu reaction of the resulting alcohol afforded the olefinic azide 363. Intramolecular 1,3-dipolar cycloaddition of 363 resulted in the formation of the bicyclic iminium ion 364, which, on treatment with ?err-butylamine, was converted to the enamine 365. Enamine 365, without isolation, was hydroborated to afford swainsonine acetonide 362, along with a small amount of the indolizidine diol 366 (Scheme 46). A novel approach to swainsonine (309) from the hydroxy lactam 367 via intramolecular cyclization to form an enantiomerically pure cyclic acyliminium ion intermediate was achieved by Miller and Chamberlin (122). The requisite lactam 367 was prepared in four steps from D-(-)lyxose. Mesylation of 367 was followed by spontaneous formation of the acyliminium ion intermediate and subsequent cyclization to yield the indolizinone 368 as a single diastereomer. The ketone dithioacetal368 was converted to the a-bromo ester by treatment with NBS, and subsequent treatment with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) gave the unsaturated ester 369. Treatment of 369 with Meerwein’s reagent, followed by reduction with NaBH,CN, did not terminate at the vinylogous ester 370, but instead resulted directly in the formation of a single, fully saturated indolizidine (371). The C-8 ketone 372 was prepared by a-hydroxylation

363

362

365 S C H E M E 46.

364

366

Reagents: a, Br-Ph3Pt (CH2)dCI. KN(TMS)?;b. (PhO)?P(O)N1,Ph3P. DEAD;

c, PhH; d, ‘BuNH2; e, BH3-THF; f. NaOAc. H 2 0 2 ;g, 6N HCI: h, IRA-400 ion-exchange

chromatography .

3.

237


of ester 371 followed by LiAIH, reduction to the diol and oxidative cleavage with NaIO,. Reduction of 372 with Na/NH, gave the desired equatorial alcohol 373, which was transformed by removal of the cyclohexylidene ketal moiety into (-)-309 (Scheme 47). A noncarbohydrate route to (-)-309 by Ikota and Hanaki (124) was achieved by way of face-selective osmylation of the optically active butenolide 374 ( 1 2 3 , available from (R)-glutamic acid (Scheme 48). Cisdihydroxylation of 374 followed by protection of the diol gave the isopropylidene derivative 375, which was converted by successive reduction, mesylation, and azidation to the azido mesylate 376. Pyrrolidine construction to 377 was effected by reduction accompanied by concomitant cyclization via intramolecular S,2 displacement. Introduction of both a threecarbon unit and the fourth stereocenter (C-8) to give the target molecule was achieved by oxidation of the dibenzylated pyrrolidine 378 followed by diastereoselective allylation. Swern oxidation of 378, followed by allylation of the resulting aldehyde with Grignard reagent, furnished the desired diastereomer 379 and its epimer 380 in a ratio of 3 : I . Successive hydroboration-oxidation of 379, mesylation, and debenzylation afforded the desired ( 4 - 3 0 9 . The same operation for 380 provided 8-episwainsonine

QM -1ao g-] d,e

f-h

0

369

-

0

371

370

i

(-)-309

373 372 SCHEME 47. Reagents: a, MsCI, Et,N; b, NBS; c, DBU: d , Et,OtBF,-: e. NCHBH,; f, LDA, 0,; g, LiAIH,; h, NaIO,; i, Na/NH3:j , 6 M HCI.

238

HlROKl TAKAHATA A N D T A K E F U M I MOMOSE

-

a,b

Q..,,,OTr

0

374

0x0

8 0 x 0

ref. 123

(RJ-glutamicacid

-

..,,,OTr

0

0x0 ..,,,OTr

375

BnO

OBn

BnO

OBn

..,,,OTr

Bn

H

378

377

V

379 ref. 125

V : / O H

I

4

0-1

(-)-309

0

D-ribonolactone

SCHEME 48. Reagents: a, catalytic OsO,, 4-methylmorpholine N-oxide; b, 2,2-dimethoxypropane, TsOH; c, LiAIH,; d, MsCI, pyridine; e , NaN,; f, H2, Pd black; g, BnBr, K2C03; h, conc. HCI; i, MOMCI, N,N-diethylaniline; j , 10% HCI; k , BnBr, NaH; 1, 10% HCI; m, (COCI)2, DMSO, Et3N; n, allylmagnesium bromide; 0,BH3; p, H 2 0 2 ,NaOH; q, MsCI, Et3N; r, H2. Pd/C, HCI.

(381). The key intermediate 378 was also obtained from D-ribonolactone by the same group (125). Hart and co-workers developed a synthesis of (-)-309 from the tartarimide 382 via radical-initiated cyclization as a crucial step (Scheme 49). (126). Mitsunobu reaction of 382, accessible from D-tartaric acid, with acetylenic alcohol provided the tartarimide 383. Reduction of 383 followed by sulfenylation of the resulting carbinol lactam gave the radical precursor 384, which on cyclization afforded a mixture of geometric isomers of indolizidines (385). Ozonolysis of 385 followed by stereoselective reduction of the resulting ketone furnished the C-8 hydroxyl (386). Inversion of the stereochemistry of C-1 of 386 was achieved by displacement of the triflate by the acetate ion to give 387. Removal of the lactam carbonyl was carried out by desulfurization via the thiolactam. Subsequent deacylation provided (-)-309. Finally, a number of syntheses of stereoisomers of swainsonine (309) such as 1-epi- (388) (1277, 8-epi- (381) (123,128),8a-epi- (389) (128,129), 8,ga-diepi- (390) (128,130), 2,ga-diepi- (391) (130), 1 $-diepi- (392) (1277,

3.


385

386

239

387

SCHEME 49. Reagents: a, Ph3P, DEAD, PhCCCH2CH2CH20H;b, NaBH,; c, "Bu3P, PhSSPh; d, "BulSnH; e, AIBN; f, 03;g, Me& h, NaBH4; i, Me3CCOCI (PivCI), DMAP, pyridine; j, NH3, MeOH; k, Tf20; I, KOAc, 18-crown-6; m, Ac,O, Et,N, DMAP; n, ( p MeOC6H4PS2)2; 0,Raney Ni; p, MeNH2.

and 2,8-diepiswainsonine (393) (115), as shown in Fig. 9, have been developed.

C . CASTANOSPERMINE Castanospermine (310), isolated from seeds of the Australian legume Castanospermum australe (131) and the dried pods of Alexa leiopetala (132), is a potent, competitive, and reversible inhibitor of several glucosi-

381

390

388

39 1

389

392

393

FIG.9. Stereoisomers of swainsonine.

240

H l R O K l T A K A H A T A A N D T A K E F U M I MOMOSE

H

HoO

HO"'

OH a

HO&

H2

H

Hoo

d

HO

HO

31 0

OH

394

395

FIG. 10. Naturally occurring stereoisomer5 of castanospermine.

dases (133). It has potential for treatment of diabetes (1341, obesity (13% cancer (136),and viral infections (1377, including human immunodeficiency virus-1 (HIV-1) (138). Stereoisomers of castanospermine, 6-epicastanospermine (394) (139) and 6,7-diepicastanospermine(395) (140),also have been isolated from Castunospermum uustrule (Fig. lo), and both inhibited amyloglucosidase. It is likely that other stereoisomers and analogs of these compounds will also inhibit glucosidase and potentially result in providing materials possessing interesting and useful biological properties. In the previous review ( I ) , only one synthesis of 310 was cited (141). To date, a number of syntheses of 310 have been achieved. Recently, an excellent review by Burgess and Henderson of synthetic approaches to stereoisomers and analogs of castanospermine has appeared (142).Most syntheses of 310 inevitably utilize carbohydrates as starting materials because of the sugar-like structure. This section reviews syntheses of the 1,6,7,8-tetrahydroxyindolizidines310, 394, and 395 isolated from natural sources (Fig. 10). Other analogs are not discussed. The absolute stereochemistry was confirmed during the first total synthesis of 310 by Bernotas and Ganem to be (IS,6S,7R,gR,SaR) (141). The protected D-glucopyranose 396 was transformed via amide 397 into the epoxide 398. Cleavage of the amide group in 398 with NaBH, followed by spontaneous cyclization gave the desired piperidine 399 and the azepane 400. Swern oxidation of 399 provided the aldehyde 401, which was immediately treated with tert-butyl lithioacetate to afford I : 1 mixture of the diastereomers 402 and 403. The less polar epimer 402 was transformed by hydrogenolysis and acid treatment into the lactam 404. Reduction of which with DIBAL gave (+)-castanospermine [( +)3101. The same reaction sequence transformed the more polar epimer 403 into 1-epicastanospermine (405) (Scheme 50). Hashimoto and co-workers reported a synthesis of ( + )-310 involving double cyclization of the epoxy amino ester 406, utilizing a strategy similar to that adopted in the indolizidine ring formation of swainsonine (Scheme 42) (143). The D-mannose-derived diol 407 was transformed in four steps into the aldehyde 408, which was epimerized by treatment with K,CO,

3.

397

396

399

+

24 1


401

390

402

404

+

400

405 403

SCHEME 50. Reagents: a, BnNH,: b, LiAIH,; c , trifluoroacetylation; d. TBDMSCI, imidazole; e . mesylation: f. "Bu4NF;g, MeONa: h. NaBH4: i , (COCI)?. DMSO, Et,N: j, terfbutyl lithioacetate: k, hydrogenolysis; I , trifluoroacetic acid; rn,DIBAL.

in MeOH to give aldehyde 409, which possesses the requisite stereochemistry. Aldehyde 409 was converted in seven steps to the epoxy alcohol 410, which was then oxidized to the aldehyde 411. Without isolation. aldol reaction of 411 with rm-butyl lithioacetate gave a mixture of diastereomers 412 in a ratio of 3 : 2. The transformation of 412 via protection of the hydroxyl group and subsequent hydrogenolysis to the pivotal amine 406 was followed by the double cyclization reaction to provide a mixture of indolizidinones 413 and 414. After separation, reduction of 413 with borane followed by treatment with acid afforded ( + )-310. Similarly, epimer 414 was converted to 405 (Scheme 51). Ganem and co-workers devised a stereoselective synthesis of ( )-310 via Sakurai allylation with highly selective chelation control of the Dglucopyranose-derived aldehyde 401 (Scheme 52) (144).Sakurai condensation of the aldehyde 401, prepared according to the method described earlier (see Scheme 50), with allyltrimethylsilane in the presence of TiCI, produced only diastereomer 415 as a result of the excellent stereocontrol derived from selective chelate formation between TiCl, and the a-amino carbonyl in 401. Ozonolysis of 415, followed by reduction, gave the diol 416. Selective monomesylation of 416 followed by hydrogenolysis afforded (+)-310. Good stereocontrol also operated in the Sakurai allylation of the

+

242


407

408

409

41 2

41 1

410

KI*

TBDMSO

-

OH

q,r

,,.OH Z

H

OH

n

414

405

SCHEME 51. Reagents: a, BzCI, pyridine; b, TBDMSCI, imidazole; c, 1 M NaOH; d, DMSO, DCC, TFA, pyridine; e, K2C03;f, H2NOH-HCI, NaHCO,; g, LiAIH4; h, CbzCI; i, TsOH;J, "Bu4NF; k, MsCI, pyridine; I, MeONa; m, Cr03-pyridine;n, tert-butyl lithoacetate; 0 , H,, 10% PdIC; p, methoxyethanol; q; BH3-THF; r, 6 M HCl.

D-mannose-derived aldehyde 417. The product 418 was then converted to 6-epicastanospermine (394) by the same manipulation. An efficient synthesis of ( + )-310 was achieved starting from glucuronolactone (419) by Anzeveno et al. (145) (Scheme 53). The starting material

41 7

418

394

SCHEME 52. Reagents: a, allytrimethylsilane, TiCI,; b, 0,; c, NaBH,; d, MsCI, Et3N; e, H,, PdIC.

3.


243

421

+

423

SCHEME53. Reagents: a, LDA, EtOAc; b, H,, PtO2; c, HC02H;d, Dowex 1-X2 (OH-) resin; e , LiAIH,; f, CF3C02H;g, H2, 5% Pt/C.

419, containing four of the five chiral centers in (+)-310, was converted in four steps to the hemiketal 420. Catalytic hydrogenation of 420 over PtO, via the favored conformer of the keto ester 421 gave a 7 : 2 mixture of 422 and 423. The desired alcohol 422 was transformed by successive deprotection, cyclization, and reduction into the pyrrolidine 424. Deprotection of 424 followed by hydrogenation gave ( + )-310. Carrying the epimer 423 through the same series of reactions gave 405. Miller and Chamberlin (122) reported a synthesis of ( +)-310 based on the intramolecular cyclization of an enantiomerically pure polyhydroxylated acyliminium ion adopted in the synthesis of swainsonine (309), as described earlier (Scheme 47). Preparation of the requisite hydroxy lactam 425 began with the known D-gluconolactone 426, which was treated with I ,3-dithiane, followed by lead tetraacetate oxidation, to afford the lactam 425. Mesylation of 425 was followed by spontaneous formation of the acyliminium ion intermediate and cyclization to give the epimers 427 and 428 in a ratio of 1 : 1. After separation, oxidation of 427 with singlet oxygen produced an unstable ketone, which was reduced selectively by L-Selectride to the indolizidinone 429. Reduction of 429 followed by hydrogenolysis gave (+)-310. The other epimer 428 was also transformed via indolizidinone 430 into 1 $a-diepicastanospermine 431 (Scheme 54). Gerspacher and Rapoport (146) devised a methodology to prepare ( + ) -310 and 6-epicastanospermine (394) based on stereoselective reduction

244

HIROKI T A K A H A T A A N D T A K E F U M I M O M O S E

427

429

+ q ~

~

6

d,e '

Brio$ fa

BnO"'

BnO'"

0

428 C.

0

0

430

431

SCHEME 54. Reagents: a, 2-(3-aminopropylidene)-l.3-dithiane;b, Pb(OAc),, AcOH; MsCI, Et,N; d, '02; e , L-Selectride; f, BH,-DMS: g, H2. 10% PdlC. HCI.

of cyclic ketone 432 (Scheme 55). The manno azide 433, obtained from D-gluco-&lactone, has four stereocenters arranged in the same manner as required for C-6, C-7, C-8, and C-8a in 394. The azide 433 was transformed in four steps into a-amino aldehyde 434, protected by a phenylfluorenyl (Pf)group, which allowed the introduction of a C? unit by an organometallic reagent. The product 435 was then cyclized in three steps to the fivemembered ring ketone 432. Reduction of 432 with NaBH, gave the alcohol 436 as a single epimer. Selective tosylation of 436 followed by removal of the Pf group, effected cyclization to give the indolizidine 437, which was then deprotected to provide the tetraol394. Synthesis of ( + b310 was accomplished by inversion of the C-6 hydroxyl in the alcohol 432. Selective acylation of 432 followed by formation of the triflate gave the pyrrolidinone 438, which was treated with acetate anion to give the inverted acetate 439. Reduction of 439 then gave a single alcohol (440).After deacetylation of 440, the resulting trio1 was converted to ( + )-310 by a series of reactions analogous to the synthesis of 394. The first synthesis of the unnatural enantiomer of castanospermine [(-I -3101 was achieved by two successive SN2-typecyclization reactions from D-xylose derivative 441 (Scheme 56) (147). Grignard reaction of the known pentose ether 441 with chelation control, followed by protection, gave

3. SIMPLE INDOLlZlDlNE ALKALOIDS

433

4

0

0

OH

434

r f n

436

432

435

j,k

437

439

I,m

-

HO

245

432

Pf

554

430

440

SCHEME 55. Reagents: a, H,, PdIC; b, PfBr, Et,N, Pb(N03),; c, DIBAL; d. NCS, Me2S; e, vinylmagnesium bromide; f, HBr; g, NaHCO?, Na2C03;h, NaBH4;i, N-methyltosylimidazolium trillate, N-methylimdazole; j , CF,COOH; k, Dowex 50W; I, Ac@, pyridine: m, (CF,S02)2,pyridine: n, Bu4NOAc; 0,AczO, pyridine, DMAP; p. K?COi.

the di-MOM derivatives 442 and 443 in the ratio 87 : 13. After separation, the major isomer 442 was subjected to ozonolysis to provide the aldehyde 444, which was followed by Hiyama-Nozaki allylation (148) under Felkin-Anh control to furnish a diastereomeric mixture of 445 and 446 in the ratio 85 : 15. The major product 445 was transformed into the mesylate 447 in seven steps. Hydrazinolysis of 447 induced cyclization to the pyrrolidine 448. After deprotection of 448, the resulting pyrroiidine alcohol was cyclized by means of a tetravalent phosphonium species in the form of the Appel reagent (Ph,P, CCI,, Et,N) (149) to afford 449, which was converted by debenzylation to (- )-castanospermine [( - 1-3101. Fleet e t a / . devised a total synthesis of 6-epicastanospermine 394 starting from L-gulonolactone (150). Three syntheses of castanospermine 310 have been performed by use of noncarbohydrate starting materials. Vogel and co-workers (151) devel-

246


OBn OBn

441

d

442

OBn OBn OH

OBn OBn OH

BnO

BnO

OMOM

445

k

443

444

OBn OBn OBn

BnO

OMOM

447

446

OBn OBn

0on H

'BuPhpSiOCH, ti

440

OMS

BnO

gBn

n

HO

449

(-)-310

SCHEME 56. Reagents: a, vinylmagnesium bromide; b, MOMCI, EtN('Pr):; c , 0, PPH3; d, ally1 bromide, CrC13, LiAIH,; e , NaH, BnBr; f , LiAIH,; g. phthalimide, PPh3, DEAD; h. HCI; i, MsCI, pyridine; j, 'BuPhzSiC1, imidazole; k, NzH,-H20; I , "Bu,NF; m, PPh,, CCI4, Et,N; n, H2, 10% pd/C, HCI.

oped a highly stereoselective synthesis of (+)-310 starting with (-) -( IS,4S)-7-oxabicyclo[2.2. IIhept-5-en-2-one [( -)-4501, "a naked sugar" (Scheme 57). Bromination of the benzyl acetal451 obtained from (-)-450 occurred on the less-hindered, convex face, and this was followed by stereoselective I ,3-migration of the endo-benzyloxy group of the acetal to afford the bromo ketone 452. Baeyer-Villiger oxidation of 452 followed by ring cleavage provided a 4 : 1 mixture of the methyl furanosides 453 and 454. The minor furanoside 454 was re-equilibrated to give 453. Furanoside 453 was transformed in three steps into the fused pyrrolidine 455 by an intramolecular S,2 aminocyclization, and it was then converted to the phosphonoacetamide 456 in three steps including the Arbuzov reaction. Intramolecular Horner-Emmons condensation of 456 followed by acetylation gave the indolizinone 457. Conversion of 457 to the epoxide 458 was followed by regioselective opening of the epoxide with H,O and acetylation to give the triacetate 459. Reduction of 459 followed by debenzylation provided (+)-310 (Scheme 57). A chemoenzymaatic avenue to (+)-310 utilizing the proline ester 460 as a chiral building block was developed by Sih and co-workers (152) (Scheme 58). The requisite chiron 460 was prepared by two procedures. First, an enzyme-catalyzed reduction of p-ketoester 461 gave 460 in over 99% enantiomeric excess. Alternatively, 460 was obtained via an enantioselective hydrolysis of the acetate (+)-462 using lipases [Pseudomonas

0

(+)-310

459

SCHEME 57. Reagents: a. BnOTMS, TMSOTf: b, Br,: c , NaHCO!: d. MCPBA, NaHCO,: e , SOCI?, MeOH; f , DIBAL; g. MsCI, pyridine; h, NH,; i , CICHzCOCl, pyridine; j, AczO, H2SOd: k , P(OEt),: I , K2C03: m, Ac?O, DMAP; n, Brz. AgOAc, AcOH. AQO: 0, 2-(ferf-butylimino)-2-[(diethylamino)imino]I ,3-dimethylperhydro- I .3.2-diazaphosphonne, polystyrene; p. 2-(t~r~-butylimino)-2-[(diethylamino)imino]-l,3-dimethylperhydro1,3,2-diazaphosphorine, polystyrene, H 2 0 ; q. A c 2 0 , DMAP: r. BH,-DMS: s, H2. PdlC.

~ . .

460

(k)- 461

460

-

0

c-e

OTBDMS

(+)-462

(2R,35)-462

(2S,3R)-460

-

h

464

463

465

TMSO

+

+

HO

467

469

468

Ik

Ik

(+)-310 HO

395

SCHEME 58. Reagents: a, Dipoduscus sp., Vogel's medium; b, Cundidu cylindrucea or Pseudomonus sp. (AK); c , TBDMSCI, imidazole: d, CF3C02H;e, methyl acrylate, Et,N; f, Na, TMSCI: g, DBU; h, TMSCI, LiN(TMS),; i, BH3-DMS: j , Me,NO; k , "BudNF.

248


sp. (AK) and Candida cylindrucea]. Conversion of 460 to the diester 463 in three steps included Michael addition. Intramolecular acyloin condensation of 463,followed by treatment with DBU, gave a mixture of indolizidines 464 and 465. Either 464 or 465 was converted to the enol silyl ether 466,which, on hydroboration/oxidation, gave a mixture of three products, 467,468,and 469).Desilylation of 468 and 469 afforded ( + 1-310and 6,7diepicastanospermine (393,respectively. A stereoselective synthesis of ( )-310 via a noncarbohydrate-based approach utilizing the chiral allylic alcohol 470, available from L-tartaric acid, was achieved by h a and Kibayashi (153) (Scheme 59). KatsukiSharpless oxidation of 470, followed by regiospecific cleavage of the resultingoxirane with Et,AINBn,, gave the 1,3-glycol471. The amino alcohol 471 was transformed in four steps into the aldehyde 472,and aldol condensation of 472 with ethyl lithioacetate provided an inseparable 89 : 1 I mixture of the p-and a-hydroxy esters 473 and 474 under p-chelation control. The diastereomeric mixture of 473 and 474 was converted to a separable

+

-

L-tartaric cid

TBDMSO

TBDMSO

470

471

,

/

-

T B D M S O ~ ~ C H O

9

Y-:

+

TBDMSO&-co2E:

MOM

472

-

Y

TBDMSO&C02Et

e.h

OTBDMS MOM

+

OTBDMS

TBDMSO

-

6H

474

473

TBDMSO

0.

j.k

MOM

475

477

470

SCHEME 59. Reagents: a, 'BuOOH. Ti('OPr)(4), diethyl L-tartrate; b, Et,AINBn,; CH3COC1, Et3N; d, MOMCI, Pr2NEt; e , LiAIH,; f, DMSO, (COCI),, Et3N; g, AcOEt. LiN(TMS),; h, TBDMSCI, imidazole; i, AcOH, Ph3P. DEAD; j, "Bu4NF;k. TsCI, pyridine; 1, H2, PD(OH),; m, Et3N; n, HCI. C,

3.

nos

SIMPLE I NDOLI ZI DI NE ALKALOIDS

249

no

31 0

ent-310 Ho,.& Ho

HO'"

OH

HO"'

405

H

Hc

O OH

~

HofY5

HO"'

HO

ent-394

395

394

ent-479

479

H O , , . g HO"'

431

480

481

482

no 483

FIG. I I . 1.6.7.8-Tetrahydroxyindolizidines synthesized to date,

mixture of the p-alcohol 475 and the a-alcohol 476. After conversion of the 0-alcohol 475 to 476 by Mitsunobu inversion, the a-alcohol 476 was transformed in two steps into the tosylate 477. Hydrogenolysis of 477 gave the protected indolizidine 478, which was deprotected by treatment with HCI-MeOH to provide ( + )-310. Three isolated products, 310, 394, and 395, plus a further nonisolated ten compounds, namely, ent-310 (147), I-epi-405 (14/,143,145,/47,~53), L-6-epi-ent-394( I N ) , L-1 ,6-diepi-ent-479, (/50), 1,6-diepi-479(150), 1 $adiepi-431 (122),8-epi-480 (144) 1,6,8-triepi-481(154),1,7,8-triepi-482(/54), 483 (/54),of the possible 32 stereoisoand 1,6,7,8-tetraepicastanospermine mers of 1,6,7,8-tetrahydroxyindoIizidine have been obtained to date (Fig. 1 I).

250


VI. Summary Investigation of synthetic routes to the simple indolizidine alkaloids has been active. With increased interest in the pharmacological properties of indolizidines, it is expected that further methodologies will be developed.

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3.


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3.

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-CHAPTER 4-

CHEMISTRY AND BIOLOGY OF CARBAZOLE ALKALOIDS D. P. CHAKRABORTY of' Nirtririil Prodrrcts Cdcrrttn 700 036. Itidia

Institute

1. Introduction ................................................. 11. Occurrence ............................................................................... 111. Chemistry of Carbazole Alkaloids .................................................

................ 258 Tricyclic Alkaloids from Higher Plants Tricyclic Alkaloids from Other Source 290 Synthesis of Tricyclic Alkaloids ........................................................ ........................ 297 Tetracyclic Alkaloids from Higher Plants 306 Tetracyclic Alkaloids from Streptomyces ............................................ F. Synthesis and Transformation of Tetracyclic Alkaloids ..... G. Hexacyclic Alkaloids from Higher Plants ........................ H. Penta- and Hexacyclic Alkaloids from Aspergillus.. .......... .............................. 317 1. Hexa- and Octacyclic Indolocarbazoles J. Synthesis of Hexacyclic Bases ............ .............................. 331 K. Biscarbazole Alkaloids .................................................................... 332 ................ 347 L. Synthesis of Biscarbazoles IV. Physical Properties of Carbazole Alkaloids .............................................. 349 A. Ultraviolet Abso B. Infrared Spectra C. NMR Spectra ... D. Mass Spectra ................................................................................. 350 ............... 350 E. X-Ray Crystallography ... V. Biogenesis of Carbazole Alk VI. Biochemical and Medicinal Properties of Carbazole Alkaloids and Related Compounds .................................. .... 352 A. Antimicrobial Properties .................................................................. 352 B. Antitumor and Tumor-Promoting Activity. ............ C. Antiviral Activity ............................................. D. Cardiovascular-Modulating Activity ..................... ................................. 356 E. Central Nervous System Activity F. Anti-inflammatory Properties .......................................... G. Modulation of Enzyme Activity, Metabolism, and Allergic R ........................ 359 H. Miscellaneous Effects References ......................................................................................... 360 A. B. C. D. E.

257 T H E A L K A L O I D S . VOL. 44 Copyright h IY93 hy Aciidemic Pre\\. Inc. All rightc of reproduction in a n y form reberved

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D. P. CHAKRABORTY

I. Introduction Graebe and Glaser (1) discovered carbazole (1) from abiological coal tar. The first carbazole from a biological source, the alkaloid murrayanine (2), was isolated by Chakraborty et al. in 1962 (2) from Murraya koenigii Spreng. The structure and antibiotic properties of murrayanine (2) were published in 1965 (3,4).Since then several reviews on carbazole alkaloids have appeared (5-13). This chapter reviews work published after the review in this treatise by Husson in 1985 ( 9 ) .

11. Occurrence

Carbazole alkaloids were first isolated from the taxonomically related genera Murrayu, Glycosmis, and Clausena of the family Rutaceae (subtribe Clausanae, subfamily Aurantodoae). The genera Micromelum (Rutaceae) and Ekebergia (Meliaceae) have also been reported to elaborate carbazole alkaloids (13). Murraya euchrestijolia, obtained from Taiwan, has been found to be the richest source of carbazole alkaloids, providing a variety of novel structures. Some bioactive carbazole alkaloids have been reported from other sources (actinomycetes, blue-green algae) and from mammalian systems. From the aspect of structural considerations, tricyclic to octacyclic alkaloids have been reported. The occurrence of alkaloids reviewed after Husson ( 9 ) is summarized in Table I .

111. Chemistry of Carbazole Alkaloids

A. TRICYCLIC ALKALOIDS FROM HIGHER PLANTS 1. Carbazole Carbazole (1, CI2H9N,mp 225°C) was reported from Glycosmis pentaphylla. It was identified based on IR, UV, and mass spectral data as well as from direct comparison with a pure sample (14).

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CHEMISTRY AND BIOLOGY OF CARBAZOLE ALKALOIDS

259

TABLE I OCCURRENCE OF CARBAZOLE ALKALOIDS Compound (formula no.)

Source (Ref.)

Tricyclic alkaloids from higher plants Carbazole (1)

Glycosmis pentaphylla Retz. (DC) (14) Murraya euchrestifolia Murrayafoline-A (3) Hyata (15) Murraya koenigii Spreng. (16) 2-Hydroxy-3-methylcarbazole (4) M . koenigii (16) 2-Methoxy-3-methylcarbazole (7) M . euchrestifolia (17) Murrayastine (8) M . euchrestifolia (17) Murrayaline-A (9) M . koenigii (18) Mukoline (17) M . koenigii (18) Mukolidine (20) M . koenigii (19) Koenoline (27) M . euchrestifolia (20) 3-Formylcarbazole (29) M . euchrestifolia ( 2 l c ) 3-Formyl-7-hydroxycarbazole (29) M . euchrestifolia (20) N-Methoxy-3-formylcarbazole (30) N-Methoxy-3-hydroxymethylcarbazole (35A) M . euchrestifolia (21c) Clausena lansium (21a) 3-Formyl-6-methoxycarbazole (36) M . koenigii (23) Mukonal (37) Murraya siamensis (24) 0-Methylmukonal (38) M . siamensis (24) 7-Methoxy-0-methylmukonal (39) Clausena harmandiana Pierre (25) 7-Methoxymukonal (40) C. lansium (21a) 6-Methoxymurrayanine (41) Clausena anisata (26) 0-Demethylmurrayanine (42) Glycosmis pentaphylla (27) Glycozolidal (43) M . euchrestifolia (28) Murrayaline-B (45) M . euchrestifolia (28) Murrayaline-C (46) C. lansium (21a) Carbazole-3-methylcarboxylate (47) C . lansium (21a) Carbazole-3-carboxylic acid (48) C . lansium (21a) 6-Methoxycarbazole-3-methylcarboxylate

(49) Murrayafoline-B (50) Isomurrayafoline-B (52) Clausenapin (53) Glycomaurrol (55) Euchrestine-A (57) Euchrestine-B (58) Euchrestine-C (59) Euchrestine-D (60) Euchrestine-E (62) Murrayanol(63) Eustifoline-C (64) Ekebergenine (66) Murrayaline-D (67) 7-Methoxyheptaphylline (68A)

M . euchrestifolia (22) M . euchrestifolia (30) Clausena heptaphylla ( I I ) Glycosmis mauritiana (32) M . euchrestifolia (33) M . euchrestifolia (33) M . euchrestifolia (33) M . euchrestifolia (33) M . euchrestifolia (34) M . koenigii (35) M . euchrestifolia (36) Ekebergia senegalensis (37) M . euchrestifolia (34) Clausena harmandiana (25) (continued)

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D. P. CHAKRABORTY

TABLE I (continued) Compound (formula no.) Carbazoloquinones Murrayaquinone-A (69) Murrayaquinone-B (51) Murrayaquinone-C (87) Murrayaquinone-D (88) Tricyclic alkaloids from other sources Hyellazole (89) 6-Chlorohyellazole (90) I-Methylcarbazole (103) I-Acetylcarbazole (104) Carbazomycin-C (105) Carbazomycin-D (106) Carbazomycinal (107) Carbazomycin-E 6-Methoxycarbazomycinal (109) Carbazomycin-F Carbazomycin-G (110) Carbazomycin-H (111) Carazostatin (112) 3-Chlorocarbazole (120) Tetracyclic alkaloids Furanocarbazoles Eustifoline-D (177) Furostifoline (178) Pyranocarbazoles Dihydroxygirinimbine (179) Pyrayafoline-A (183) Pyrayafoline-B (186) Pyrayafoline-C (190) Pyrayafoline-D (191) Pyrayafoline-E (193) Mukonicine (194) Glycomaurin (eustifoline-A) (195) Eustifoline-B (195A) 7-Methoxymurrayacine (199) Isomahanine (201) Heptazolicine (201A) Pyranocarbazoloquinones Pyrayaquinone-A (202) Pyrayaquinone-B (203) Pyrayaquinone-C (208) Tetracyclic alkaloids from Strepiomyces Kinamycin-A (216)

Source (Ref.)

M. M. M. M.

euchrestifolia euchresiifolia euchresiijolia euchresiifolia

(29) (29) (29) (29)

Hyella cuespiiosa Born et Flah (40) H . caespitosa (40) Tedaniu ignis (42) Tedania ignis (42) Sireptoueriicillium ehimense H-1051-NY 105 (43) S. ehimense (43) s. sp. (44) S . ehimense (43) s. sp. (44) S. ehimense (43) S. ehimense (45) S. ehimense (45) Strepiomyces chromofuscus DC 118 (46) Bovine urine (48)

M . euchresiijolia (36) M . ruchresiifolia (36) M . euchresiijolia (60) M . euchresiijolia (61) M . euchresrifolia (33) M . euchresiijolia (33) M . euchrestijolia (33) M . euchresiijolia (28) M . koenigii (62) Glycosmis mauriiiana (32) M . euchresiifolia (36) Murruya siamensis (24) M . kornigii (35) Clausena hepiaphylla ( 6 ) M . euchresiijolia (62) M . euchresiijolia (62) M . euchrestijolia (20) Sirepiomyces murayamaensis (64,65a,h )

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CHEMISTRY A N D BIOLOGY OF CARBAZOLE ALKALOIDS

261

TABLE I (continued) Compound (formula no.) Kinamycin-B (217) Kinamycin-C (209) Kinamycin-D (218) Prekinamycin (219) Ketoanhydrokinamycin (220) Kinamycin-E (221) Kinamycin-F (deacetylkinamycin-C) (212) Hexacyclic alkaloids from higher plants ( + )-Murrayazoline (241) Murrayazolinol (245) Penta- and hexacyclic alkaloids from Aspergillus Tubingensin-A (246) Tubingensin-B (247) Alfavazole (249) Hexa- and octacyclic Indolocarbazoles Arcyriaflavin-B (252) Arcyriaflavin-C (253) Protein kinase C inhibitor K-252c (262) Protein kinase C inhibitor K-252d (263) Rebeccamycin (254) AT 2433-A1 (272) AT 2433-A2 (273) AT 2433-B 1 (274) AT 2433-82 (275) Staurosporine (251) Tan-1030A (293) Tan-999 (296) Protein kinase C inhibitor K-252a (297) Protein kinase C inhibitor K-252b (298) UCN-OI (298A) Biscarbazoles Indole dimer (305) Bismurrayafoline-A (306) Chrestifoline-D (307B) Bismurrayafoline-B (308) Bismurrayafolinol (309) Oxydimurrayafoline (311) Murrafoline-F (312) Murrastifoline-A (313) Murrastifoline-B (314) Chrestifoline-A (315)

Source (Ref.) S. murayamaensis S.murayamaensis S.murayamaensis S.murayamaensis S.murayamaensis S . murayamaensis S.mrrrayamaensis

(64,65a,b) (64,65a,b) (64,65a,b) (66.67) (67) (67) (67)

M. euchrestifolia (29) M . koenigii (79) Aspergillus tubingensis (80) A . tubingensis (81) Aspergillus f l a w s (82) Arcyria denudata (85) A . denudata (85) Nocardiopsis sp. K-290 (91,92) Nocardiopsis sp. (91,921 Nocardia aerocolonigenes (86-88) Actinomadura melliaura sp. nov. (SCC 1655) (93,94) A . melliaura sp. (93,94) A . melliaura s p. (93,94) A . melliaura sp. (93,94) Streptomyces staurosporsus Anaya, Takahashi, and Omura sp. nov. (83,84) Streptomyces sp. C-71799 (98,99) Nocardiopsis dassonvillei (98,99) Nocardiopsis sp. K-252 and K-290 ( I 00,92) Nocardiopsis sp. (91,92) Streptomyces sp. ( l o l a ) Murraya gleni (102) Murraya euchrestifolia (15) M . euchrestifolia ( 2 l c ) M. euchrestifolia (15) M . euchrestifolia (30) M. euchrestifolia (30) M. euchrestifolia (20) M . euchrestifolia (103) M . euchrestifolia (103) M . euchrestifolia (103)

(continued)

262

D. P. CHAKRABORTY

TABLE I (confinued) Compound (formula no.) Bismurrayafoline-C (316) Bismurrayafoline-D (317) Murrafoline-B (319) Murrafoline-D (320) Murrafoline-E (321) Murrastifoline-D (322) Murrastifoline-E (323) Chrestifoline-B (324) Murrastifoline-C (325) Chrestifoline-C (326) Murrafoline-C (327) Murranimbine (328) Bis-7-hydroxygirinimbine A (328A) Bis-7-hydroxygirinimbine B (328B) Murrafoline (329)

Source (Ref.) euchresfifolia (28) euchrestifolia (28) euchresfifolia (104) euchresfifoh (104) euchrestifoh (20) euchrestifoliu (103) M . euchrestifolia (105) M . euchresfifolia (103) M . euchrestifoliu (103) M . euchrestifoh (103) M . euchrestifoliu (104) M . euchrestifolia (106) M . euchrestifolia ( 1 0 6 ~ ) M . euchrestifolia ( 1 0 6 ~ ) M.euchrestifoh (107) M. M. M. M. M. M.

2. Murruyufoline-A From an ethanolic extract of the root bark of Mirrruyu euchrestfoliu Hyata, murrayafoline-A [3, C,,H,,NO (M+21I ) , mp 52-57"CI was obtained as colorless plates (15). The 1-methoxycarbazole skeleton in 3 was readily detected from the characteristic UV spectrum [A, 225, 243, 251 (sh), 283 (sh), 292, 330, 344 nm, with log E 4.47, 4.58, 4.44, 3.83, 4.01, 3.53, 3.491 and was supported by IR data (v,,, 1640, 1610, 1590, 1505 cm-'). The 'H-NMR data for 3 indicated that ring A was unsubstituted. The signals for an aromatic methoxy group (6 3.76) and an aromatic methyl (6 2.42, s), together with the signals for H-4 (6 7.33) and H-2 (6 6.44), showed that the methoxy group was at C-1 and the methyl at C-3. The structural assignments were substantiated by nuclear Overhauser effects (NOE) in which the enhancement of signals for H-4 and H-2 were observed arising from irradiation of the methyl at C-3 and the methoxy at C-1,respectively. From these data, murrayafoline-A was formulated as l-methoxy-3-methylcarbazole, which was previously known as a synthetic intermediate for murrayanine (6).

4.


263

3 . 2-Hydroxy-3-methylcarbazole

The roots of M . koenigii furnished (16) a compound with the formula C,,H,,NO (M+ 197) and a melting point of 245°C (4). From the IR (urnax3520, 3400, 1635, 1600 cm-') and U V (A, 235, 254, 258, 304, 322 nm with log E 4.65,4.25,4.26,4.19, 3.66) spectral data, the isolate was considered to be a phenolic carbazole. The 'H-NMR data showed that it has a phenolic group (6 8.1), a methyl substituent (6 2.37), and an unsubstituted ring A; signals were observed for H-4 (6 7.68) and H-1 (6 7.0). The characteristic U V spectrum of acetate 5 for 3-methylcarbazole (6) and its isolation from 4 by zinc dust distillation confirmed the position of the methyl group at C-3. From these data, compound 4 was assigned the structure 2-hydroxy-3-methylcarbazole, which was confirmed by 13CNMR data and direct comparison with a synthetic specimen (6).

4. 2-Methoxy-3-methylcarbazole

From a petroleum ether extract of the seeds of Murraya koenigii, an isolate with the formula C,,HI3NO (7, mp 245°C) was obtained (16). The IR (v,,, 3425, 1640, 1600, 1708, 820, 750 cm-') and UV (A, 235, 255, 300, 328 nm with log E 4.35, 3.8, 3.9, 3.30) spectra showed it to be a carbazole derivative. 'H-NMR data showed that ring A was unsubstituted, and signals for an aromatic methoxy group (6 3.77), and an aromatic Cmethyl (6 2.35) as well as for H-4 (6 7.5) and H-1 (6 6.95) were observed. On zinc dust distillation, the compound furnished 3-methylcarbazole ( 6 ) , and on demethylation it furnished 2-hydroxy-3-methylcarbazole (4). Consequently, the isolate was formulated as 2-methoxy-3-methylcabazole (7) (6).

5 . Murrayastine From the bark of Murraya euchrestifolia, murrayastine [8, C,,H,,NO, 224, 247, 255, 298, 332) and (M' 271.1191)] was isolated (17). UV (A, IR data showed it to be a carbazole alkaloid, and the 'H-NMR spectrum showed an aryl methyl signal (6 2.47), aryl methoxy groups (6 3.95, 3.96,

264

D. P. CHAKRABORTY

and 4.0), and meta-coupled H-4 (6 7.32) and H-2 (6 6.65) signals. The enhancements of the H-4 and H-2 resonances on irradiation of the aryl methyl group showed that the methyl group was at C-3. The ortho-coupled H-5 signal (6 7.56, d, J = 8 Hz) showed that C-5 and C-6 were unsubstituted. A 1,7,8-trimethoxy-3-rnethylcarbazolestructure for 8 is consistent with the physical data and has been confirmed by synthesis.

OCH3

CH3O

CH~O

H

OCH;

CHO

6. Murrayalinr-A

From the bark of M. ei~hrrstifolim, murrayaline-A [9, C,,HISNO3 ( M + 269.1002), mp 248.5"CI was obtained as pale yellow prisms (17). The U V and IR data showed the isolate to be a carbazole derivative with a , ~ cm-I). The 'H-NMR spectrum hydrogen-bonded formyl group ( v , , , ~1640 showed signals for an aryl methyl (6 2.35), two aromatic methoxy groups (6 3.90, 3.99, H-4 (6 7.95, s) and H-1 protons (6 6.91, s), and orthocoupled H-5 (6 8.02, d , J = 9 Hz) and H-6 protons (6 6.77, d, J = 9 Hz). In NOE experiments irradiation of the methyl caused enhancement of the H-4 signal, whereas irradiation of the methoxy signals resulted in enhancement of the H-1 and H-6 signals, indicating that the methoxy groups were located at C-2 and C-7. From these data, murrayaline was carbazole (9), which has formulated a 2,7-dimethoxy-3-methyl-8-formyl been confirmed by synthesis. Synthesis of Murrayastine and Murrayaline-A. Alkaloids 8 and 9 were synthesized using the diphenylamine route (17). l-Bromo-2-methoxy-4methylbenzene (lo), on reaction with 5,6-dimethoxyaniline acetate (11) in pyridine in the presence of Cu and K,CO,, followed by hydrolysis, provided the diphenylamine derivative 12 required for the synthesis of murrayastine. On the other hand, l-bromo-3-methoxy-4-methylbenzene (13) on reaction with the dimethyl acetal of 6-formyl-5-methoxyaniline acetate (14) furnished the diphenylamine derivative 15. On hydrolysis, compound 15 furnished the diphenylamine aldehyde 16 required for murrayaline synthesis. Compounds 12 and 16, on cyclization with palladium acetate in N,N-dimethylformamide (DMF), furnished murrayastine (8) and murrayaline-A (9), respectively.

4.


265

7 . Mukoline Mukoline [17, C,,HI,NO2 ( M + 227), mp 115-12o"C], isolated from the roots of Murraya koenigii ( I @ , indicated the presence of a I-methoxycarbazole chromophore with an additional alcoholic hydroxyl group, based 221, 242, 252, 255, 280, 290, 320 nm with log E 4.60, 4.85, on UV ,A( 4.65,4.0, 3.4, 3.6, 3.0) and IR (v,,, 3440, 3240, 1610 cm-') data and color reactions. In the 'H-NMR spectrum, a benzylic methylene (6 4 . 7 3 , a hydroxyl group (6 4 . 9 , and an aromatic methoxy group (6 3.9), besides the signals for H-5, H-4, and four other protons of the carbazole nucleus, were discernible. The isolate afforded the N-methyl derivative 18 and an 0-acetate 19 with a U V spectrum similar to that of 17, showing that the hydroxyl group was not phenolic. On oxidation with active MnO,, 17 furnished aldehyde 20 (mp 152-155"C), the UV spectrum of which was similar to that of 3-formylcarbazole. On decarbonylation 20 furnished 1-methoxycarbazole (21). From the nonidentity of 20 with murrayanine (2) and other data, mukoline was formulated as l-methoxy-6hydroxymethylcarbazole (17).

8. Mukolidine Mukolidine [20, C,,H,,N02 (M+ 225), mp 152-55"C], isolated from M . koenigii (18), was shown by IR and UV spectroscopy to be a 3formylcarbazole derivative. From the 'H-NMR data, the presence of an aldehydic proton (6 10.8) and an aromatic methoxy group (6 4.25), in addition to the aromatic proton signals, including those of H-4 and H-5, was readily discernible. The physical data for mukolidine and the identity of its borohydride reduction product with mukoline, as well as its identity

266

D. P. CHAKRABORTY

Q +H3c'0\ -

HOHC

(23) N=NCI +

0

NHN (2.4)

(22) H

3

c

I

i

+

w

0

Dehydrogenation methylation 4

( Diazomethane)

H (25)

OCH~

(26)

'

O

I D D Q oxdn.

(20)

Sodium borohydride

reduction -

(17)

with the oxidation product of mukoline, showed it to be l-methoxy-6formylcarbazole (20). The structures of both 17 and 20 have been confirmed by synthesis as follows. 2-Hydroxymethylenecyclohexanone (22) on condensation with diazonium chloride (23,) obtained from p-toluidine under JappKlingemann conditions, furnished the hydrazone 24, which on indolization furnished the ketotetrahydrocarbazole 25. Dehydrogenation (Pd/C) and subsequent methylation with diazomethane furnished l-methoxy-6methylcarbazole (26). On oxidation with 2,3-dichloro-5,6-dicyano-l,4benzoquinone (DDQ), 26 furnished mukolidine (20), which on subsequent reduction with sodium borohydride, yielded mukoline (17). 9. Koenoline

Koenoline (27, C,,H,,N02, mp 213"C), isolated from the root bark of Murraya kocnigii (19), displayed a UV spectrum (A, 225, 241, 251, 258, 279, 289, 323, 335 with log E 3.58, 3.63, 4.04, 3.86, 4.36, 4.22, 4.71, 4.56)

4.


267

f&-JqCH20R

H

OCHJ

(27)R = H ;( 2 8 ) R = COCH3

that indicated the presence of a 1-methoxycarbazole chromophore. The IR spectrum (v,,, 3445, 3235 cm-I) showed the presence of NH and OH groups, and the isolate formed a monoacetate (28, mp 110°C). In the 'HNMR spectrum, the presence of an aromatic methoxy (6 4.01), a benzylic methylene (6 4 . 3 , H-4 (6 7.66, lH, br s), a H-2 proton (6 6.95, lH, br s), s), and an unsubstituted ring A were readily discernible. Consequently, (27) the formulation of koenoline as 1-methoxy-3-hydroxymethylcarbazole was rational and was confirmed from I3C-NMR data and partial synthesis from murrayanine (2) by sodium borohydride reduction (6). w

c

H

2

O

H

Sodium borohydride reduction

"

OCH3

(2)

( 27)

10. 3-Formylcarbazole From Murraya euchrestifolia, 3-formylcarbazole [29, C13H,N0 (M+ 195.0683)] was obtained as a colorless oil (20). It was identified from its characteristic UV spectrum, which was also supported by IR and

H (29) R = H (29A) R = OH

I

O C H ~ (30) R =CH0;(35A)

R = CH2OH

'H-NMR data. 3-Formylcarbazole reported from Clausena fansiurn (21a) melted at 158-159°C like synthetic 29 (mp 153-154°C) (21b). 11. 3-Formyl-7-hydroxycarbazole

From Murraya eucharestifolia, 3-formyl-7-hydroxycarbazole [29A, C,,H,NO, (M+ 21 l)] was obtained as a colorless powder. The structure was determined from physical (UV, IR, 'H NMR) data ( 2 1 ~ ) .

268

D. P. CHAKRABORTY

12. N-Methoxy-3-formylcarbazole

From M . euchrrstifolia, the oil N-methoxy-3-formylcarbazole [30, C14HIINOZ (M+ 225.04)] was isolated (20). UV (A,, 236, 272, 288, 320 nm) and IR (Y,,, 1690 cm-I) spectral data showed it to be a 3-formylcarbazole derivative. The 'H-NMR spectrum indicated signals for a 3formylcarbazole except that the signal for N-H was replaced by a methoxy group (6 4.27). These data led to formulation of the isolate as N-methoxy3-formylcarbazole, which has been confirmed by synthesis as described below (22). Treatment of 4a,9a-cis-l,2,3,4,4a,9a-hexahydroxycarbazole (31) with methyl chloroformate in methylene chloride and trimethylamine produced the corresponding 9-methoxycarbonyl compound 32 (mp 68-69°C). The 6-iodo derivative 33 was obtained by treatment of 32 with iodine and sodium periodate, and reaction of 33 with 30% aqueous HIOz and sodium tungstate, followed by methylation with diazomethane, furnished 1,2,3,4tetrahydro-6-iodo-9-methoxycarbazole (34),from which the 6-formyl compound 35 was obtained by treatment with butyllithium in tetrahydrofuran (THF) and quenching in dry DMF. The formyl derivative, on dehydroge(30). nation with DDQ in benzene, afforded 9-methoxy-3-formylcarbazole

Methyl c h l o r o f o r m a t e in CHZCIZ+N(CH~)~

I

H (31)

COOCH3 (32)

A Ikali n e hydrolysis, sod. t u n g s t a t e 0xdn.I and m e t h y l a t i o n

I

OCH3

(3L)

I

C 0OC H - j

(33)

4.


269

13. N-Methoxy-3-hydroxymethylcarbazole From M . euchresrifolia (21c), N-methoxy-3-hydroxymethylcarbazole [35A, CI4Hl3NO2 (M+ 227.0895)] was isolated as a colorless oil. From the UV, IR, 'H-NMR, and I3C-NMR data it was considered to be N-methoxy3-hydroxymethylcarbazole. The proposed structure was further supported by conversion of 35A to 3-hydroxymethylcarbazole by catalytic hydrogenation and by NaBH, reduction of 30 to yield 35A.

14. 3-Formyl-6-methoxycarbazole 3-Formyl-6-methoxycarbazole [36, C I 4 H'NOz I ( M + 225), mp Clausena lunsium (21a), showed a UV spectrum 135-136"C], isolated from (A, 229, 245, 281, 297, 334 nm with log E 4.38, 4.17, 4.35, 4.47, 3.80) similar to that of 3-formylcarbazoles. The structure of 36 was established from 'H-NMR data, which were similar to those for glycozoline with the aryl methyl signal being replaced by a signal for a formyl group.

(36)

15. Mukonal From the stem bark of M . koenigii (23),mukonal [37, C,,H,NO, (M+ 211), mp 238"CI was isolated. From the UV (A,, 234, 247, 278, 297, 342 nm with log F 4.42, 4.21, 4.54, 4.58, 4.06) and 1R (v,,, 1640 cm-') data, and its color reactions, the isolate was considered to be a 3-formylcarbazole derivative with a chelated hydroxyl group. The 'H-NMR data showed the presence of an unsubstituted ring A, an H-4 singlet (6 8.4) deshielded by the formyl at C-3, a chelated hydroxyl (6 11.76), and an aldehydic proton at C-3 (6 10.16). From these data, a 2hydroxy-3-formylcarbazole formulation of mukonal (37) was advanced, which was supported by the "C-NMR spectrum and the identity of the isolate with an authentic sample of 3-formyl-2-hydroxycarbazole ( 6 ) . 16. O-Merhylmukonal

O-Methylmukonal [38, C,,HI,N02 (M' 225), mp 189-189.5"CI was obtained from the roots of Murruya siamensis (24). The U V and IR

270

D. P. CHAKRABORTY

data suggested the presence of a 3-formylcarbazole skeleton. From the 'H-NMR data, an unsubstituted ring A, an aromatic methoxy group (6 4.50), an aldehydic proton (6 10.45), deshielded singlets for H-4 and H-5(6 8.50 and 7.12), and a singlet for H-1 were detected. The 3-formyl2-methoxycarbazole formulation for 0-methylmukonal(38) was consistent with the above data and was supported by I3C-NMR data. 17. 7-Methoxy-0-methylmukonal 7-Methoxy-0-methylmukonal [39, C,,H,,NO, (M+ 255.0875), mp 219-220"Cl was obtained from Murruya siumensis (24).The UV and IR data suggested the presence of a 3-formylcarbazole system, and the 'HNMR data for 39 were similar to those for 38 with the exception of an additional methoxy group (6 3.85). The signals for H-5(6 7.97, d , J = 8.3) and H-6 (6 6.83, dd, J = 8.3,2.2) showed that H-5 was ortho-coupled, whereas H-6 was both ortho- and meta-coupled, suggesting the location of an additional methoxy group at C-7. Consequently, formulation 39 was consistent with the data and was subsequently confirmed by 13C-NMR data. 18. 7-Methoxymukonal 7-Methoxymukonal [40, CI,H,,NO, (M+ 241)] was isolated from the root bark of Clausena harmandiana (25). U V (A, 222, 238, 244, 254, 288, 302, 340 nm with log E 4.27, 4.30, 4.30, 4.20, 4.33, 4.54, 3.8) and IR (vmax 3350, 1619 cm-') data for the isolate showed the presence of a 3formylcarbazole skeleton with a hydroxyl group chelated to the formyl group. The 'H-NMR data were very similar t o those of 39 except that the methoxy group was replaced by a hydroxyl(6 1 I .56) chelated to the formyl group (6 9.88) at C-3. From these data, formulation of the alkaloid as 2hydroxy-3-formyl-7-methoxycarbazole(40) was advanced and later confirmed by I3C-NMR data. 19. 6-Methoxymurrayanine 6-Methoxymurrayanine [41, CI5Hl3NO3 (M+ 255), mp 23 1-233"C], isolated from Clausena lansium (21a), showed UV data characteristic for a 3-formylcarbazole derivative (A,, 239, 251, 287, 294, 335, 349 nm with log E 4.35, 4.20, 4.40, 4.36, 3.85, 3.30), which was also supported from IR data. The 'H-NMR data showed the alkaloid to possess an additional methoxy group as well as signals for murrayanine. From the 'H-NMR data for H-5, the methoxy group was placed at C-6. This conclusion was also supported by I3C-NMR data.

4.


271

20. O-Demethylmurrayanine

O-Demethylmurrayanine [42, C,,H,NO, (M+2 1 I), mp 237-239"Cl was isolated from the root bark of Clausena anisata (26). From the IR and UV spectra (A, 226, 244, 255, 278, 291, 336, 346 nm with log E 4.40, 4.50, 4.39, 4.59, 4.45, 4.22, and 4.22) and color reactions, the isolate was considered to be a phenolic 3-formylcarbazole derivative. 'H-NMR spectroscopy showed that ring A was unsubstituted and that it had metacoupled signals for H-4 and H-2, as well as an aldehydic proton at 9.89. The hydroxyl group was located at the 1 position, and the l-hydroxy-3formylcarbazole structure for 42 was further supported by the 13C-NMR spectrum. 21. Glycozolidal

Glycozolidal [43, C,,H13N0, (M+ 255), mp 185"C], isolated from the roots of Glycosmis pentaphylfa (27), appeared to be a 3-formylcarbazole derivative, judging from the UV ,,A( 235, 245, 303, 340 nm with log E 4.4, 4.2, 4.2, 4.06) and IR (vmax 3500, 1675 cm-I) data. The 'H-NMR spectrum showed the presence of a formyl group (6 9.9), two aromatic methoxyl groups, a singlet for the H-4 proton (deshielded because of the formyl at C-3), and a meta-coupled H-5 proton (6 7.6), besides the signals for three other aromatic protons (H-1, H-7, and H-8). Thus, structure 43 was advanced for glycozolidal, which was confirmed by synthesis from glycozolidine (44)by DDQ oxidation.

22. Murrayaline-B Murrayaline-B [45, C15H,,N03(M+ 255), mp 240-247"C], isolated from 223, 259 (sh), Murraya euchrestifolia (28),showed a UV spectrum [A,

272

D . P. CHAKRABORTY

303, 380 nm] similar to that of murrayaline-A (9). The 'H-NMR spectrum of 45 showed the presence of an aryl methyl (6 2.34), a methoxy group (6 4.02), a C-8 aldehydic proton (6 10.58), H-4 (6 7.79) and H-5 protons (6 8.16), and two deuterium-exchangeable protons at 6 8.42 and 10.79. In NOE experiments, irradiation of the aromatic methoxy (6 4.02) and aryl methyl signals (6 2.34) showed enhancement in the H-6 (6 6.89) and H-4 (6 7.73) signals, demonstrating that the aromatic methoxy was at C-7 and the aromatic methyl at C-3. On methylation with CHJ, murrayaline-B (45)furnished murrayaline-A (9).

-

(9)

OH

23. Murrayaline-C

Murrayaline-C (46, C,,H,,NO,), obtained as a pale yellow powder from M . euchrestifolia (28),had a UV spectrum similar to that of murrayalineA (9). The 'H-NMR spectrum showed signals similar to those for murrayaline-B, except that it had an additional aldehydic proton signal (6 9.95) chelated to a hydroxyl group (6 11.41) replacing the methyl at C-3. Thus, the structure of murrayaline-C was assigned as 46.

24. Carbazole-3-methylcurboxylate

Carbazole-3-methylcarboxylate [47, C,,H, ,NO2 (M 225), mp 168-170°C], isolated from Clausena lansiirm ( 2 1 ~ 1showed , a U V spectrum [A, 241, 251, 273 (sh), 287, 320, 332, 346 nm with log E 4.57, 4.50,4.57, 4.68 (sh), 3.82 (sh), 3.73 (sh), 3.301 typical of a carbazole derivative. The 'H-NMR spectrum showed a signal for a COOCH, group and other signals for a carbazole derivative. From the 'H-NMR data alkaloid 47 was considered to be carbazole-3-methylcarboxylate. +

4.


273

25. Carbazole-3-carboxylic Acid Carbazole-3-carboxylic acid (48, C,,H,NO,, mp 270-272"C), also isolated from Clausena lansium (21a),showed absorption maxima in the UV at 230, 237, and 269 nm (log E 4.18, 4.7, 4.22). From the 'H-NMR data and the identity of its methyl ester with 47, the compound was formulated as carbazole-3-carboxylic acid (48). 26. 6-Methoxycarbazole-3-methylcarboxylate

6-Methoxycarbazole-3-methylcarboxylate [49, C,,H,,NO, (M 255), mp 147-14SoC], isolated from Clairsena Iunsium (21a).showed a UV spectrum characteristic for a carbazole derivative. 'H-NMR and IR data revealed a methoxycarbonyl function. 'H-NMR spectroscopy showed a signal for an aromatic methoxy group (6 3.91) and other signals for the protons of a carbazole nucleus, and compound 49 was considered to be a 6-methoxy3-methylcarboxylate. +

27. Murrayajkline-B Murrayafoline-B [50, C,,H,,NO, (Mi 295)] was obtained as a colorless syrup from Murraya euchrestifolia (29). The UV data of 50 (A,, 234,254, 304, 338 nm) and its shift in alkali showed it to be a phenolic carbazole, which was consistent with the IR data (v,,, 3600, 3475, 1620, 1595 cm-I). The 'H-NMR spectrum of 50 showed the presence of an aromatic methoxy group (6 3.90), an aromatic methyl group (6 2.42), and a dimethylallyl side chain (6 1.88, 1.72, 3.90, 5.31). In addition, it showed two broad

274

D. P. CHAKRABORTY

singlets arising from the H-4 and H-2 protons and ortho-coupled H-5 and H-6 proton signals. Photooxidation of murrayafoline-B (50) gave murrayaquinone-B (51)(29), and thus murrayafoline-B was represented by structure 50.

28. Isomurrayafoline-B Isomurrayafoline-B [52, CI9H,,NO, (M+ 295.1567), mp 158-161"C] was obtained from M. euchrestifoliu (30).The IR and UV spectra ,X,(, 213, 237, 264, 310, 330 (sh)] showed it to be a carbazole derivative. The 'HNMR spectrum showed the presence of an aromatic methoxy (6 3.90), an aromatic methyl (6 2.38), a hydroxyl function (6 4.74), and signals for H-5 (6 7.70, d, J = 8 Hz) and H-4 (6 7.67, s). Enhancement of the H-4 and H-6 signals by irradiation of the aromatic methyl and aromatic methoxy signals, respectively, showed that the methyl was at C-3 and the methoxy group at C-6. From these data, structure 52 was assigned as isomurrayafoline-B, an isomer of 50.

29. Clausenapin

Clausenapin [53, C,,H,,NO ( M + 279), mp IOI"C] was obtained from Clausena heptaphylla (31). The UV spectrum (A, 224, 240, 250, 290, 320,335 nm with log E 4.55,4.50,4.59,4.29,5.39,5.50) showed the isolate to have a I-methoxycarbazole chromophore, which was also supported by the IR data. In the 'H-NMR spectrum, signals for an aromatic methyl (6 2.28), a dimethylallyl side chain (6 1.75, 1.85, 3.62, and 5.31, t), an unsubstituted ring A, and a H-4 singlet were observed. Carbazole (1)and 3-methylcarbazole (6) were obtained by zinc dust distillation of 53, and

4.


275

compound 54 was obtained by cyclization with HBrIacetic acid. From these chemical studies, structure 53 was assigned to clausenapin, which was previously reported as the Huang-Minlon reduction product of indizoline (6). 30. Glycomaurrol

Glycomaurrol [55, C,,H,,NO (M+ 265.1466), mp 149-15o"C], isolated from the stem bark of Glycosmis mauritiana (32),was shown by U V [A, 230, 243 (sh), 255 (sh), 268 (sh), 289, 298, 327 nm with log E 4.15, 4.08, 3.97,3.89,3.79,3.88,3.05]and IR spectroscopy to be a phenolic carbazole. 'H-NMR data showed the presence of a dimethylallyl side chain [6 I .76, 1.95 (3H, s each), 3.99 (d, J = 6.5 Hz), 5.40 (d, J = 6.5 Hz)], a phenolic hydroxyl (6 4.68), and an aromatic methyl group (6 2.52), in addition to the aromatic proton signals similar to those of glaucomaurrol. From these data, glycomaurrol was considered to be 3-methyl-5-(3',3'-dimethylallyl)6-hydroxycarbazole ( 5 9 , which was confirmed by conversion to dihydroglycomaurin (56).

31. Euchrestine-A

Euchrestine-A [57, C,,H,,NO, (M+ 281.1414)] was obtained as a colorless oil from M. euchrestifolia (33). The UV spectrum of 57 showed the presence of a 2,7-oxygenated carbazole chromophore. The 'H-NMR spectrum showed the presence of an aromatic methyl (6 2.3% a dimethylally1 side chain [6 1.78, 1.89 (3H, s), 3.59 ( 2 H , d), 5.36 (t, J = 6.7 Hzl, unsubstituted H-4 and H-1 protons, and ortho-coupled H-5 and H-6 protons. By comparison of the 'H-NMR data with those of isomurrayafolineB, structure 57 was assigned to euchrestine-A.

32. Euchrestine-B Euchrestine-B [58, C,,H2,N0, (M+ 363.2173)], a pale yellow oil from M. euchrestifolia (33), showed a UV spectrum, like 57, characteristic of

276

D. P . CHAKRABORTY

(57) (58) (59) (60)

R1

R2

H

H

R3 DMA

R.4

Euchrcstinc-A Euchrestine-B Euchrestine-C Euchrcstinc-D

H

H

H

Gcranyl Gc rany I

H Gcranyl H

CH3 H H

Gcranyl H H 0 x 0 Gcranyl

CH3 H

H

H

(61) O-Dimethyl Euchrcstinc -D (62) Euchrestinc-E

CH3

H

Abbr. :

DMA=

0 x 0 Gcranyl =

+ ; Gcranyl=

/

/

.s

a 2,7-dioxygenated carbazole. From the 'H-NMR data, the presence of H-4, H-1, and ortho-coupled H-5 and H-6 protons were discernible. The compound showed signals for an aromatic methoxy (6 3.90), an aromatic methyl (6 2.38), and the protons of a geranyl side chain [6 I .57, 1.62, 1.88 (3 methyl, s), 2.06 (4H, m), 3.62 (2N, d, J = 6.7 Hz), 5.32 (lH, t , J = 6.7 Hz), 5.07 (lH, m)]. In NOE experiments, irradiation of the methoxyl group led to enhancement of the H-6 resonance, proving the methoxy group to be at C-7. From these data, euchrestine-B was assigned structure 58. 33. Euchrestine-C Euchrestine-C [59, C2,H,,N02 (M+ 349)] was obtained as a brown powder from M. euchrestifolia (33).Like euchrestine-A and -B, it had a UV spectrum characteristic for a 2,7-dioxygenated carbazole system. The mass spectral peak at mlz 266 (M+ - 83) and the 'H-NMR signal for HI (6 6.81), together with the similarity to euchrestine-B of signals for other aromatic protons and an aromatic methyl, but without the methoxyl signals, allowed placement of the geranyl chain at C-8. Consequently, structure 59 was consistent with the physical data for euchrestine-C. 34. Euchrestine-D (M+ 349.201 l)] was obtained as a pale Euchrestine-D [60, C23H27N02 yellow oil from M . euchrestiJofia (33).The U V data were similar to those

4.


277

for other euchrestines, suggesting the presence of a 2,7-dioxygenated carbazole system. The 'H-NMR data showed signals for the H-5 (6 7.74, dd, J = 8.4, 1 Hz), H-6 (6 6.88, dd, J = 8.4, 2.4 Hz), H-8 (6 6.82, d, J = 2.4 Hz), and H-4 protons (6 7.56), as well as signals for a geranyl side chain. The 0-dimethyl ether 61 also showed similar signals for the aromatic protons and geranyl chain, besides signals for two aromatic methoxy groups. From these data, structure 60 was assigned to euchrestine-D, which was substantiated by NOE data.

35. Euchrestine-E Euchrestine-E 162, C,,H,,NO, (M+ 365.1993)] was obtained as a pale brown oily racemate from M . e u c h r e s t i f o h (34). 'H-NMR spectroscopy of 62 showed signals for an aryl methyl (6 2.38), an H-4 proton (6 7.651, and an H-5 (6 7.66) doublet coupled with H-6 (6 6.73, d , J = 8.4 Hz). 'H-'H correlation spectroscopy (COSY) data showed the presence of three directly coupled protons (6 2.84, 3.10, and 3.99) arising from a benzylic methylene and adjacent methine bearing an oxirane ring, suggesting the presence of a geranyloxy chain. Another methylene proton signal (6 2.17) coupling with an olefinic proton (6 5.07) and other oxymethine protons overlapping with signals of ally1 methyls and methyls attached to oxygen were observed. The 'H-NMR data of 60 and 62 were similar, except for some signals in the geranyloxy chain of 62, with the mass spectral peak at mlz 226 (M+ - 139) being due to loss of a fragment from the geranyloxy chain. These data showed structure 62 to be consistent for euchrestine-E; however, the stereochemistry of 62 was not assigned. 36. Murruyanol

Murrayanol [63, C,,H,,NO, (M+ 363.2196), mp 161"C], isolated from M . koenigii ( 3 3 , showed UV [A,, 208,236,262,296,316,328; log E 4.66, 4.69, 4.88, 4.25 (sh), 4. I 1 (sh), 4.631 and IR spectra typical for a phenolic carbazole derivative. 'H-NMR spectroscopy showed signals for a geranyl side chain [6 1.57, 1.63, 1.88 (Me groups), 3.62 (2H,J = 6.7 Hz), 5.02-5.12 ( I H , s) 2.06-2.09 (4H, m), 5.33 ( l H , m)], as well as H-5 (6 7.74) H-4 (6 7.72, l H , d, J = 8.6 Hz), H-8 (6 6.80), and H-3 protons (6 6.83, l H , J = 1.6 Hz), an aromatic methyl at C-6 (6 2.38), and an aromatic methoxy at C-7 (6 3.91). These data established the compound to be l-geranyl-2-

OH

278

D . P. CHAKRABORTY

hydroxy-6-methyl-7-methoxycarbazole(63). The structure of murrayanol (63) has also been supported by mass spectral (13) and I3C-NMR data. 37. Eustifoline-C

Eustifoline-C [64, C,,H2,N0 (M+ 333)] was obtained as a brown powder from M. euchrestifolia (36). The UV and IR data suggested the presence of a 3- or 6-oxygenated carbazole skeleton. 'H-NMR data showed the presence of an aromatic methyl group (6 2.51), a hydroxyl function (6 4.901, and a geranyl side chain [6 1.56, 1.63, 1.94 (3H, s each), 2.09 (4H, m), 4.0 (2H, d, J = 6.4 Hz), 5.05 (IH, m), and 5.41 ( I H , J = 6.4 Hz)] which was also supported by the mass spectral peak at mlz 210 (13). In NOE experiments, irradiation of the benzylic methylene of the geranyl chain caused enhancement of the H-4 signal, (6 7.90) whereas irradiation of the methoxy group of the 0-methyl derivative (65) of eustifoline-C enhanced the H-7 signal (6 7.08). These data indicated that the hydroxyl group in 64 was at C-6 and the geranyl chain at C-5; thus, eustifoline-C is represented as structure 64. Geranyl I

\

38. Ekebergenine

Ekebergenine [66, Cl9HI9N0,(M+ 293), mp 230-23loC] was obtained from Ekebergia senegalensis (Meliaceae) (37). The 'H-NMR spectrum of the N-methyl derivative 66A (C,,H,,NO,, mp 155- 157°C) showed signals for an aldehyde (6 10.37), one aromatic methoxy (6 3.99), and an N-methyl (6 4.13) group, as well as signals for a dimethylallyl side chain (6 1.70, 1.89, 4.19, 5.28, t). In addition, it showed signals for H-5 (6 8.10), H-6 (6

Y ( 6 6 ) R = H ;(66A) R = CH3

4.

CHEMISTRY A N D BIOLOGY OF CARBAZOLE A L K A L O I D S

279

7.70), H-7 (6 7 . 9 , H-8 (6 7.4), and H-2 protons (6 7.4). It lacked signals for H-4, H-3, and H-1, thereby allowing assignments of the substitutions in ring C. 13C-NMR data for 66A, including heteronuclear correlation spectra, confirmed the structures of N-methylekebergenine (66A) and ekebergenine (66). 39. Murrayaline-D

Murrayaline-D [67, C,,H,,NO, ( M + 377.1984)] was obtained as a brown oil from M . euchrestifofia (34). In the 'H-NMR spectrum, signals for a methoxy (6 3.93, an aldehydic function at C-3 (6 9.98), ortho-coupled H5 and H-6 protons (6 7.88, 6.95, J = 8.8 Hz each), singlets for H-1 and H-4 protons (6 7.40, 8.08), and signals for a geranyl side chain [a 1.56, 1.60, 1.91 (3H each), 2.10 (4H, m), 3.68 (2H), 5.08 (IH), and 5.36 ( l H , t)] were readily discernible. The mass spectral peak at mlz 254 represented by the ionic species 68 (13) also confirmed the geranyl side chain in 67. From NOE experiments, the E configuration of the double bond of the side chain was suggested. Enhancement of the proton signal at C-6 (6 6.95) showed that the methoxy group was at C-7. These data led to the formulation of murrayaline-D as 67.

CHJO

40. 7-Methoxyheptaphylline

7-Methoxyheptaphylline [68A, C,,H,,NO, (M+ 30911, isolated from Cfausena harmandiana (25), showed evidence (IR, UV, and 'H-NMR spectra) for the presence of CHO, OH, NH, and OMe functions, as well as a dimethylallyl side chain on a carbazole skeleton. By comparison of the 'H-NMR data of 68A with those of 40, the DMA chain was placed at C-1. From the 13C-NMR data for C-8 (6 95.57), the methoxy group was located at C-7. and the alkaloid was formulated as structure 68A.

280

D. P. CHAKRABORTY

41. Murrayaquinone-A

Several carbazoloquinones have been discovered in Murraya euchrestifolia. Murrayaquinone-A [69, Cl,H,,NO2 (M+ 271), mp 246-247OC1, the first carbazoloquinone alkaloid, was isolated from M . erichrestifolia (29). IR (vmaX3200, 1650, 1595 cm-I) and UV ,A[ 225, 258, 293 (sh), 395 nm with log E 4.63, 4.51, 3.85, 3.931 data showed it to be a carbazole-1,4quinone. This was substantiated by I3C-NMR data (6 180.4 and 183.4). 'H-NMR spectroscopy showed the presence of an unsubstituted ring A, an ally1 methyl signal at 6 2.19, and a vinylic proton signal at 6 6.31. From these and biogenetic considerations, the methyl was placed at C-3, showing murrayaquinone-A to be 1,4-quinonoid-3-methylcarbazole (69). Compound 69 has also been obtained by oxidation with Fermi's salt, as well as by photochemical oxidation, of 1-hydroxy-3-methylcarbazole(70). Palladium-assisted cyclization of analogs of diphenylamine derivatives has been utilized in the synthesis of murrayaquinone-A (37a). 0

H

O

42. Murrayaquinone-B Murrayaquinone B [51, C,,HI,N03 (M+ 309), mp 221-223OC1, also obtained from M . euchrestifolia (29), showed IR (v,,, 3280, 1655, 1640,

4.


281

210 (sh), 232, 264, 310 (sh), 400 nm; log E 1610 cm-') and U V [A,, 4.28, 4.58,4.44, 3.21, 3.661 data characteristic for a 1,4-~arbazoloquinone fragment, like murrayaquinone-A. This was supported by 13C-NMRdata for the carbonyl functions (6 179.8, 183.7). The characteristic ally1 methyl signal (6 2.13) and the vinylic proton (6 6.42) were readily discernible from the 'H-NMR data. In addition, signals for ovtho-coupled H-5 and H-6 protons (6 7.98, 7.02, d , J = 9 Hz), one methoxy group (6 3.91), and a dimethylallyl side chain [6 1.74, 1.85, 3.6, 5.23(t)] were observed, which

(51)CH3O

WCH O C H ~

282

D. P. CHAKRABORTY

were also supported by 13C-NMR data. From the results of NOE experiments, the methoxy group was placed at C-7 and the dimethylallyl side chain at C-8. Thus, the structure of murrayaquinone-B was advanced as 51, which was confirmed by synthesis (38). The azidocinnamate 73, obtained by condensation of 4-(1 , I-dimethylal1yloxy)benzaldehyde (74) with methyl azidoacetal(75), by heating in tolu(76). The methoxy indole ene, furnished 6-hydroxy-7-dimethylallylindole 77 obtained by methylation of 76 with CH,I, on Claisen condensation with 4-methylbutyrolactone, gave lactone 78. On heating in aqueous dioxane, 78 gave alcohol 79 (mp 79-80°C), which, on pyridinium chlorochromate oxidation, gave the aldehyde 79A. Through cyclization at room temperature with boron trifluoride etherate, 79A furnished 1,7-dimethoxy-3methyl-8-(3’-methylbut-2-enyl)-9H-carbazole (80), which, by photooxidation, furnished murrayaquinone-B (51). Synthesis of murrayaquinone-B has been achieved by Ramesh and Kapil via murrayafoline-B by several routes (39), one of which is mentioned here. 7-Hydroxy-3-methyl- 1-oxo- 1,2,3,4-tetrahydrocarbazole(81) on acetylation furnished a 7-acetoxy derivative (82), which, on aromatization with Pd/C in diphenyl ether, yielded l-acetoxy-3-methyl-7hydroxycarbazole (83) as one of the products. Condensation with 2methyl-3-buten-2-01 (84) in presence of boron trifluoride etherate gave l-acetoxy-7-hydroxy-3-methyl-8-(3’-methyl-but-2-enyl)carbazole (85). On methylation of 85, the 7-methoxy derivative 86 was obtained which,

HO

R H

O

(81) R=OH (02) R=OCOCH3

OCOCH3 (83)

4.


283

on hydrolysis with sodium acetate in methanol, gave murrayafoline-B (50). Oxidation of 86 with pyridinium chlorochromate (PCC) furnished murrayaquinone-B (51). 43. Murrayaquinone-C Murrayaquinone-C [87, C,,H,, NO, (M+ 377), mp 158-159"C], obtained from M. euchrestifolia (29), showed the presence of a 1,4-benzoquinone system in the UV (A, 233, 267, 460 nm) and I3C-NMR spectra (6 183.6 and 179.7), like other carbazoloquinones. The IH-NMR spectrum was similar to that of murrayaquinone-B (51)except that the signals for the dimethylallyl side chain were replaced by signals for a geranyl side chain [6 1.56, 1.61, 1.85 (3 methyl signals), 2.05 (4H, s), 3.58 (2H, d, J = 7 Hz), 5.03 ( I H , m), and 5.26 (IH, t, J = 7 Hz)], which was substantiated by the mass spectral peak at mlz 254. The positions of the methoxy group at C-7 and the geranyl group at C-8 were substantiated by the results of NOE experiments. Thus, murrayaquinone-C was formulated as 87. 0

(87) R1 = OCH3;Rz = Geranyl ( 8 8 ) R1 = OH ;R2 = Geranyl

44. Murrayaquinone-D Murrayaquinone-D [88, C,,H,,NO, (M+ 363), mp 164- 168"C], obtained (29)along with murrayaquinone-C, showed IR, UV, and I3C-NMR characteristics very similar to those of 87. The 'H-NMR spectrum of 88 was very similar to that of 87, with the exception that one aromatic methoxy signal was replaced by a phenolic hydroxyl group, showing the isolate to be a demethylated murrayaquinone-C, which was confirmed by methylation of murrayaquinone-D to murrayaquinone C with diazomethane. Therefore, murrayaquinone-D was formulated as 88. B. TRICYCLIC ALKALOIDS FROM OTHERSOURCES 1 . Hyellazole

The first carbazole alkaloid from a marine source (40), namely, hyellazole [89, C,,H,,NO (M+ 287), rnp 133-134"C], isolated from the bluegreen alga Hyella caespitosa, showed IR (v,,, 3490 cm-') and UV (A,,,

284

D . P. CHAKEUBORTY

226, 232, 250, 260, 292, 304, 338, 352 nm with log E 4.53, 4.55, 4.53, 4.13, 4.09, 4.26, 3.65, 3.69) spectra characteristics of a carbazole derivative. 'H-NMR spectroscopy showed the presence of an unsubstituted ring A and signals for an aromatic methoxy (6 3.79), an aromatic methyl (6 2.14), an H-4 proton (6 7.70), and five aromatic protons (6 7.6-7.35). These data (89), suggested hyellazole to be l-phenyl-2-methyl-3-methoxycarbazole which has been supported by I3C-NMR spectroscopy.

2. 6-Chlorohyellazole The 6-chloro derivative of hyellazole 190, C2,,HlhCIN0(M+ 312), mp 163-164"CI was isolated from the same source along with hyellazole (40). It displayed a 'H-NMR spectrum very similar to that of 89 except for the absence of the H-6 signal, indicating the chloro substituent to be at C-6. The proposed structures of hyellazole (89) and its 6-chloro derivative (90) were confirmed by X-ray crystallography of 6-chlorohyellazole and by several syntheses. Synthesis of Hyellazole and Chlorohyelluzole. The syntheses of 89 and 90 by Kano et al. (41) involved the formation of a 2-vinylindole derivative as the starting material. Subsequently, formation of 2,3-divinylindole and thermal ring closure of the 2,3-divinyl system led to the syntheses of the natural products as described below. N-Benzoylsulfonylindole (91) or its 5-chloro derivative (91A), on reacting with propiophenone, furnished alcohols 92 and 93. These compounds, on hydrolysis, furnished the indoles 94 and 95. In the case of hyellazole, the intermediate formyl derivative 96 was obtained by Vilsmier-Haack reaction, whereas in case of chlorohyellazole the intermediate formyl derivative was obtained via oxalyl chloride derivative 97 and the keto ester 98. Compound 98, on hydrolysis, furnished the ketoacid 99, which, by decarboxylation, afforded the formyl derivative 100. The formyl derivatives 96 and 100, on Wittig reaction, furnished the divinylindoles 101and 102, which were converted to alkaloids 89 and 90 by thermal cyclization.

4.

285


R q = R y & - J Propiono\

7

I 7O2 Ph

I

02

Ph (92) R = H

Ph (91) R = H

(93) R = C I

(91A) R = C I

J

Hydrolysis

-

~CcgJ-JCy

/

R N

(94) R = H

/

\

N

Ph

I

(95) R = C I

i

Vilsmier-Haack

R

4 0 2 C 'QJ-$y?

a

(96) R = H (100) R - CI

Ph

(97)

Ph

(98) R = E t (99) R = H

Wittiq

RQq.p I c

H

~

c

H

~

~

~

m

Ph

0

~C"3 y

s

~

\

(101) R = H (102) R = C I

/

(89) R = H (90) R = C I

3 . 1-Methylcarbazole

From the marine sponge Tedania ignis (42) was isolated I-methylcarbazole [103, C,,H,,N (M+ 181.0811), mp 120°C]. The 'H-NMR spectrum of 103 included aromatic protons typical of a carbazole system, except that H-1 was replaced by a signal for an aromatic methyl group (6 2.56).

~

~

0

c

D. P. CHAKRABORTY

286

(103) R = CH3 (lob) R = COCH3

4. I-Acetylcarbazole

Also from the marine sponge Tedania ignis was isolated l-acetylcarbazole (104, C,,H,,NO). The isolate showed in the IR spectrum the presence of an amine and an acetyl function (v,,, 3444, 1671 cm-'1. The 'H-NMR spectrum showed signals for a carbazole system and lacked the signal for a H-1 proton, showing instead a signal for an acetyl group (6 2.8, 3H, s). The physical data indicated the compound to be I-acetylcarbazole (104), which was supported by I3C-NMR data.

5. Carbazomycin-C The structural determinations of eight antibiotic alkaloids isolated from Streptoverticillium ehminse and a Streptomyces sp. by Japanese groups primarily rests on detailed work on carbazomycin-B. The chemistry of carbazomycin-A and -B has been reviewed by Husson ( 9 ) .The chemistry of the six other alkaloids (13) is reviewed here. Carbazomycin-C [105, C,,H,,N03 ( M + 291.1 19), mp 198-198.5"C], obtained from Streptoverticillium ehimense (43), was considered to be a carbazole derivative from UV data [A, 227, 248, 260 (sh), 287 (sh), 295, 341, 354 nm with E 24,900, 24,000, 12,550, 7600, 12,200, 3000,42001. The 'H-NMR spectrum showed the presence of two aryl methyl (6 2.33, 2.36), two aromatic methoxy (6 3.74, 3.84), and one hydroxyl group (6 8.06), as well as signals for meta-coupled H-5 (6 7.7), H-7, and H-8 protons (6 R2 R 3 q $ : 3

(105) Carbazomycin C ; R1 = C H 3 , R2= OH9 R 3 = OCH3 (106) Carbazomycin D; R1 = C H 3 9 R2 = R 3 = OCH3

(107) Carbazomycinal ; R1 = CHO Y R2 = OH * R 3 = H (108) 0-Methyl carbazomycinal;Ri = C H O , R 2 = OCH3, R 3 = H (109) 6-Methoxy carbazomycinal; R1 = CHO * R 2 = OH * R3 = OCH3

4.


287

6.91 and 7.3 dd). These data suggested a formulation of I ,2-dimethyl-3,6dimethoxy-4-hydroxycarbazole for carbazomycin-C (105). This has been supported by I3C-NMR data in which the methoxy-induced shifts of C-6, C-5, C-7, C-8, and C-8a were reported at 6 154 (s), 106.2 (d), 113.9 (i), 1 11.5, and 135.6. The structure was confirmed by X-ray crystallographic studies. 6. Carbazomycin-D

Carbazomycin-D [106, C,,H,,NO, (M+ 285.1374), mp 129.5-130"Cl (43) showed IR and UV data similar to those of carbazomycin-C. Compared to the 'H-NMR data of carbazomycin-C, it had an additional aromatic methoxy group, which suggested it to be the O-methyl ether of carbazomycin-C. This was confirmed by methylation of carbazomycinC with dimethyl sulfate and alkali to yield carbazomycin-D. Thus, carbazomycin-D was formulated as 106.

7. Carbazomycinal Carbazomycinal [107, CI5Hl5NO3 (M 255.0875), mp 224"C], isolated from a member of the genus Strrptouerticillii~m(44),was considered to be a I-formylcarbazole derivative from IR (vmax1660 cm-l) and UV (A,, 214, 227, 263, 295, 320, 372 nm with F 24,400, 23,200, 12,200, 16,300, 5000,8400) data. From the 'H-NMR data, ring A was considered unsubstituted, and I3C-NMR data confirmed the presence of a carbonyl group. NOE enhancement after irradiation of the methyl group showed proximity to the formyl group, suggesting the methyl to be at C-2. In the IH-NMR spectrum of O-methylcarbazomycinal (lOS), the signal of the additional O-methyl group was deshielded (6 3.8) owing to ring A, which suggested that the hydroxyl group of carbozomycinal was at C-4. Thus, carbazomycinal was formulated as 1 -formyl-2-methyl-3-methoxy-4-hydroxycarbazole (107). +

8. 6-Methoxycarbazomycinul

Along with carbazomycinal was isolated an antibiotic substance [109, C,,H,,NO, (M+ 285.1017), mp 221"CI (44).Like carbazomycinal, the UV (A,, 215, 227, 245, 268, 310, 382 with E 27,000, 24,500, 13,000, 13,000, 17,000,8500) and IR data for the isolate showed it to be a I-formylcarbazole derivative. The IH-NMR spectrum, as conipared to carbazomycinal, showed an additional methoxy group that was placed at the 6 position in view of the meta-coupled signals of €3-5 (6 7.72, d , J = 2.4 Hz) and orthocoupled H-8. In a long-range selective proton decoupling experiment (LSPD), irradiation of H-3 caused collapse of both C-4b and C-6, whereas collapse of the signals for C-7 and C-8a was observed on irradiation of

288

D. P. CHAKRABORTY

H-5 and collapse of C-5 and C-8a on irradiation of H-7. The alkaloid was therefore formulated as 6-methoxycarbazomycinal (109) which was supported also by I3C-NMR data. Nakamura and co-workers isolated both carbazomycinal and its 6-methoxy derivative and named them carbazomycin-E and carbazomycin-F (43). 9 . Carbazomycin-G

Carbazomycin-G [110, CI5H,,NO, (M 257), mp 241-243"C], isolated from Streptoverticillium ehimense (4.9, showed UV and IR data suggesting a carbazole chromophore. The 'H-NMR data showed signals for two aromatic methyl (6 1.60, 2.01), and one aromatic methoxy (6 3.7), and H5 [6 8.05 (deshielded by C=O at 4)], H-6, H-7, and H-8 protons (6 7.21-7.50). The I3C-NMR spectrum showed signals for a tertiary methyl (6 27.9), a quarternary carbon (6 67.3) carrying a hydroxyl, a vinylic methyl (6 10.10), and a methoxyl group (6 59.2). The carbonyl signal at 6 177.5 could be reconciled with a 2-methoxydienone formulation. From these data carbazomycin-G could be represented by structure 110, which has been confirmed by X-ray crystallographic analysis. +

(110) Carbazomycin G ; R = H ( 1 1 1 ) Carbazomycin H ; R = OCH3

10. Carbazomycin-H

Along with carbazomycin-G was isolated carbazomycin-H [111, C,,H,,N04 (M+ 287), mp 228-230°C](45). The similarity of the IR and UV spectra with those of carbazomycin-G suggested a similar chromophoric system. The 'H-NMR spectrum showed an additional methoxy group (6 3.84) as compared with carbazomycin G. The H-5 signal was meta coupled (6 7.66, d , J = 2.4 Hz) and showed a diamagnetic shift of 0.57 ppm as compared with that of 110, which could be due to the position of the methoxy group at C-6. The methoxy-induced shifts of the aromatic protons of ring A were in conformity with the assignment of the methoxy at C-6. Thus, carbazomycin-H (111)was identified as 6-methoxycarbazomycin-G. 1 1 . Carazostatin Carazostatin [ l U , C2,H25N0 (M+ 295), mp 149-152"C], isolated as a pale yellowish powder from Streptomyces chromofuscus DC 118 (461,

4.

CHEMISTRY A N D BIOLOGY OF CARBAZOLE A L K A L O I D S

289

displayed IR (v,,, 3460, 3360 cm-I) and U V (A,,,, 218, 235, 254, 266,303, 342; E 153,000, 141,000, 76,000, 60,000, 83,000, 20,000) data that showed it to be a phenolic carbazole. The 'H-NMR spectrum showed signals for an aromatic methyl (6 2.38) and H-4 (6 7.3), H-5 (6 7.94, dd, J = 8.0, 1.5 Hz), H-6 (6 7.17, ddd, J = 8.0, 8.0, 1.5 Hz), H-7 (6 7.37, IH, ddd, J = 8.0, 8.0, 1.5 Hz), and H-8 protons (6 7.42, dd, J = 8.0, 1.5 Hz), demonstrating that ring A and C-4 were unsubstituted. Dimethylcarazostatin (113) showed signals for an aromatic methoxy (6 4.05) and an N methyl (6 3.9) group. The signals for a normal heptyl chain were readily ascertained (6 2.87, 1.65, 1.46-1.30, 8 H , m, 0.91, 3H and J = 7.0 Hz for the C-methyl). Like many carbazoles of microbial origin, the aromatic

H

(120)

290

D. P. CHAKRABORTY

methyl was placed at C-2 and the hydroxyl at C-3. Thus, carazostatin could be formulated as l-heptyl-2-methyl-3-hydroxycarbazole(112), which has also been confirmed by I3C-NMR data and synthesis (47). Diels-Alder reaction of 1-heptylpyrano [3,4-b]indole-3-one (116) [prepared from indolylacetic acid (114) with octanoic anhydride (115)l with 3-trimethylsilylpropynoate (117) afforded carbazole (118,) which, on reduction, gave carazostatin (112). 1,2-Dialkyl-3-trimethylsilylcarbazole (119) also furnished carazostatin (112) when it was mercurodesilylated followed by hydroboration and oxidation in the same reaction sequence used in case of hyellazole (89) and carbazomycin-B (127). 12. 3-Chlorocarbazole

One alkaloid, 3-chlorocarbazole 1120 ( M + 201)], was obtained from bovine urine (48). From IR, UV, and 'H-NMR data (6 7.18-7.50, 7H, m and 6 7.90-8.15,3H, m), it was considered to be 3-chlorocarbazole, which was confirmed by direct comparison with a synthetic specimen.

C. SYNTHESIS OF TRICYCLIC ALKALOIDS The tricyclic carbazole alkaloids have attracted the attention of synthetic organic chemists because of their structural novelty and biological activity. As a result, various new strategies have been developed to synthesize these alkaloids. Transition metal-catalyzed metal diene complexes have been utilized in the total synthesis of carbazomycins, koenoline, murrayanine, and mukonine. For the synthesis of carbazomycin-A and -B, iron tricarbonyl hexadiene complex (121) has been utilized in the electrophilic aromatic substitution (122, 123) at room of 2,3-dimethyl-4-methoxy-5-hydroxy/methoxyaniline temperature (49). The 5-methoxy derivative provided the substituted product 124 on standing for 3 days, whereas the substituted product 125 was obtained after 2 hr of refluxing. Acetyl derivative 126, on MnO, oxidation, gave O-acetylcarbazomycin-B (127A). Deacetylation of 127A gave carbazomycin-B (127). Selective oxidation of 124 furnished the iron-complexed product 128, demetallation of which with methylamine oxide gave 3demethylcarbazomycin A (129). Methylation of 129 furnished carbazomycin-A (130). Optimized iron-mediated amine cyclization (50) has been utilized for broad and general access to 1-oxygenated carbazole alkaloids, resulting in the synthesis of mukonine (131), murrayanine (2), koenoline (27). The iron complexed cation 121, when reacted with arylamines 132 and 135, furnished the iron-complexed intermediates 133 and 136, which, on cyclization under different experimental conditions, furnished the alkaloids

4.


1

?CH3

OH

H (130)

(132)

(133)

CH3

291

292

D. P. CHAKRABORTY

mukonine (131) and murrayanine (2). Reduction of murrayanine (2) furnished koenoline (27).

N H2

N 02 (134)

(135) CH3CN

I

; 25OC

Mn02

Toluene

Lewis acid-catalyzed aliphatic diazo coupling has been utilized in the synthesis of glycozoline (141) by Chakraborty and Roy (13). Iodinecatalyzed thermal cyclization of anthranilic acid (142) has been found to yield carbazole (1) as one of the products (51).

C

H

$

m

c

H

3

W-K. reduction -dc h y drogc nat ion

H

H

O

4.


293

3-Methylcarbazole (6), glycozoline (141), and glycozolidine (44) have been synthesized from appropriate diphenylamines using degassed Raney nickel in the presence of p-cymene in a sealed tube (13). R 2 0 , N n ‘ 1 H 3

Degassed Raney n i c k e i

H

H

Synthesis of murrayafoline-A was reported by Martin and Moody (52). Under Claisen condensation conditions, reaction of indole-2-methylcarboxylate (144) with 4-methylbutyrolactone (145) yielded the product 146, from which the alcohol 147 was obtained by hydrolysis and decarboxylation. Oxidation of 147 with PCC gave the aldehyde 148, which on cyclization with boron trifluoride-methanol gave murrayafoline-A (3).

CO 0 C H3

H (ILL)

(1L 5 ) H O (146) Hydrolysis and Decar b o x y l a t i o n

294

D. P. CHAKRABORTY

2-Hydroxy-3-methylcarbazole (4). an important biogenetic intermediate, has been synthesized by Bergman and Carlson (53)via alkylation of 2-methylindole (149) with aldehyde 150. Reaction of 2-methylindole (149) with a,@-unsaturatedketone 152 in the presence of Pd/C and a molecular sieve afforded a better yield of 2-methylcarbazole (153), a key intermediate in the pathway to most of the carbazole alkaloids of fungi and bacteria (54). 2-Hydroxy-3-methylcarbazole (4) was also obtained by biomimetic hydroxylation (Fe2+,EDTA, and oxygen) of 3-methylcarbazole (6) (55). CHO

I

C H 3C H-CO 0 C2H 5

CH3

--

(150)

H (149)

H (151)

+

1

9 R1

Cat 10% Pd, HOAc r x L8 h r

R = CH3 R1 = R2 = (1521

CH3 (153)

H

Biomimetic

(6)

Hydroxylation-

(L)

Diels-Alder reaction for the synthesis of carbazomycin and hyellazole using indole-2,3-quinodimethaneanalogs pyrano [3,4-h]indole-3-one (154) and 155 has been utilized by Moody and Shah (56). Diels-Alder reaction of 154 with trimethyl silylpropynoate (117) gave carbazole 156, which, on reduction with LiAIH,, yielded the 2-methylcarbazole derivative 158. Mercurodesilylation of 158 gave 160, which by hydroboration and oxidation gave phenol 162. On methylation, the phenol gave 4-deoxycarbazomycin-B (164). Starting with 155, following the reaction sequence 155 + 157 + 161 + 163, hyellazole (89) was obtained. Treatment of 4-deoxycarbazomycin B (164) with N-bromosuccinimide, following protection of the NH group with a tert-butoxycarbonyl group (165), afforded the 4-bromo derivative 166. Subsequent treatment of 166, with l-butyllithium in THF at -78"C, followed by reaction with aryllithium and trimethylborate and alkaline hydrogen peroxide treatment, provided the 4-hydroxy derivative 61. After removal of the N-butoxycarbonyl group carbazomycin-B (127) was obtained. Pindur and Pfeuffer (57) synthesized 4-demethoxycarbazomycin-A(164) and its isomer using [4 21 cycloaddition reactions of appropriate die-

+

4.


(156) R = C H 3 (157) R = Ph

(154) R = C H 3 (155) R - P h

W

H

q

1 cAH3

O

c

4

H R (160) R = CH3 (161) R = P h

(158) R = CH3 (159) R = P h

1

Hydro bo ra t i o n oxidation

woH c H3

\

>

\

H R (162) R = CH3 (163) R = P h

W

t-BUO

C

A.

H CH3 3

cH3

= t-BUO

(165)

(167)

A.

bH3

295

296

D. P. CHAKRABORTY

nophiles to a 3-vinylindole. Bergman and Pelcman (54) synthesized 3demethoxyhyellazole (168) starting from 2-vinylindole through several steps using cycloaddition reactions. A new synthesis of 3-demethoxycarbazomycin-B (169) has been reported by Bergman et al. in which intramolecular acyl indole cyclization has been utilized (58). A convenient synthesis of hyellazole has been effected by benzannelation of 2-methoxyindolin-3-one (170) by Sakamato and co-workers (59) Wittig reaction of 170 with phosphonium compound 171 gave 172, which yielded 3-buta- 1,3-dienylindole (173) after reaction with trimethylsilylindole in the presence of hexamethyldisilazane (HMDS). On heating, 173 yielded 174 via an electrocyclic reaction. Ready removal of methanol from 174 gave 3-hydroxycarbazole derivative 175 and the silyl ether 176. The

OCH3 Ac

(170)

(171)

i

c

(175) R = H ( 1 7 6 ) R = Si(CH3)3

(89) R = H (176A) R = A c

4.

CHEMISTRY AND BIOLOGY OF CARBAZOLE A L K A L O I D S

297

latter, on treatment with tetra-l-butylammonium flouride (TBAF), afforded 175, from which hyellazole (89)was obtained after methylation and deacetylation. ALKALOIDS FROM HIGHER PLANTS D. TETRACYCLIC

Pyranocarbazoles of the girinimbine and mahanimbine groups constitute the largest classes of the tetracyclic alkaloids from higher plants. Furanocarbazoles and benzo[b]carbazoles of the kinamycin group constitute further additions to these groups. 1 . Eustifoline-D

Eustifoline-D [177,C,,H,,NO ( M + 221.08411, obtained as a colorless oil from M . euchrestifolia (361, represents a new variant of the tetracyclic carbazole alkaloids with a furan ring system. The IR (vmaX3470 cm-I) and UV (A, 206, 224, 250, 268, 298, 310, 340, 354 nm) data, together with the 'H-NMR signals for the a-and p-furan protons (6 7.81,7.32, H1 each, d, J = 2.6 Hz), suggested a furanocarbazole system. On irradiation of H4 (6 7.97) enhancement of the p-furan proton was observed, showing that the furan was fused with the carbazole system at the 5,6 positions. These findings, together with the 'H-NMR signals for an aromatic methyl and other protons of carbazole ring system, led to the formulation of eustifoline-D at 177.

2. Furostifoline Furostifoline [178,CI5H,,NO( M + 221.0840)], obtained as an oil (36) from the same source as 177 was shown to be a 2-oxygenated carbazole derivative based on IR and UV data. The 'H-NMR spectrum of 178 showed two doublets (6 7.73, 7.00, 1H each, J = 2.0 Hz) attributable to the aand p-furan protons. The 'H-NMR data showed the absence of substitution in ring A (6 8.06, 7.25, 7.37, 7.49), one aromatic methyl, and a singlet for H-4, indicating the compound to have structure 178. This was also supported from NOE experiments when enhancement of H-4 was observed on irradiation of the methyl at C-3.

298

D. P. CHAKRABORTY

3. Dihydroxygirinimbine Dihydroxygirinimbine (179, CI8H,,NO, (M+ 297.1365), mp 189-190"C, [aID-40" (MeOH) } was obtained from the root bark of M . euchrestifolia

(60). A 3-methylcarbazole skeleton with a hydroxyl group was readily 215, 238, discernible from the IR (v,,, 3450 cm-') and UV spectra (A,, 254, 259, 303, 332 nm). The 'H-NMR data for 179 showed an absence of substitution in ring A and signals for H-4 (6 7.72, s) and the aryl methyl group at C-3 (6 2.28), showing that the C-2 was substituted. Doublets at 6 3.79 and 4.9 ( J = 8 H z each), which shifted in the diacetate 180 (mp 159-161°C) to 6 5.8 and 6.22, respectively, indicated the presence of a methine group. These data could be reconciled with a 3-methyl-2',2'dimethyldihydroxypyranocarbazolesystem in 179. Girinimbine (1811, on oxidation with chloroperbenzoic acid, furnished dihydroxygirinimbine and its cis isomer, suggesting that alkaloid 179 is trans-dihydroxygirinimbine.

(179)R = H (trans) (180 1 R = C O C H 3 (182 1 R = H ( c i s )

4 . Pyrayafoline-A

Pyrayafoline-A (183), C,,H,,NO,) was obtained the root bark of M. euchrestifolia ( 1 7 ) . The IR and UV [A,, 222, 239, 286 (sh), 295, 334 nml data suggested it to be a carbazole derivative with a 2',2'-dimethyl-A3' -pyran (DMP) system, which was substantiated by a high-intensity mass spectral peak at mlz 278 (M+ - 15) (6). The 'H-NMR spectrum showed signals for an aromatic C-methyl (6 2.33), an aromatic methoxy (6 3.89), and a DMP( system (6 1.47, 6H and two one-proton doublets at 6 5.67 and 6.58, J = 10 Hz), as well as signals for H-4 (6 7.62, s), H-5 (6 7.63, J = 8 Hz), and H-6 protons (6 7.77 br s). From these data, pyrayafolineA was formulated as 183, which was confirmed by synthesis as follows (17). The diphenylamine derivative 184, obtained by condensing l-bromo3-methoxy-4-methylbenzene (13) with 2,3-(2' ,2'-dimethyl-A3'-pyrano)anilinoacetate (185), on cyclization with Pd(Ac), in DMF furnished pyrayafoline-A (183) (17).

4.


299

5 . Pyrayafoline-B Pyrayafoline-B [186, C,,H,,NO, (M+ 279.1266)], obtained from the stem 228,252,285, bark of M. euchrestifolia (33),showed a UV spectrum [A, 296 (sh), 329, 353 nm] similar to that of carbazole alkaloids with a DMP system, and this was substantiated by a high-intensity peak at mlz 264 (M' - 15) in the mass spectrum. The 'H-NMR spectrum showed an aromatic methyl group (6 2.37), H-4 and H-5 protons (6 7.62 and 7.49), resonances for a DMP system [6 1.46, two doublets at 6.48, 5.58 (IH, J = 6 Hz each)], and aromatic signals at 6 6.74 and 6.71. The isolate afforded a monomethyl derivative on treatment with diazomethane, suggesting the presence of a phenolic group. NOE experiments on the methyl ether involving irradiation of the methoxy group and the aromatic methyl group produced enhancement of the signals for H-1 and for H-4, showing that the methyl was at C-3 and the methoxy at C-2. From these data,

H (186) R - H (189) R = C H 3

Ac

( 1 88)

t

300

D. P. CHAKRABORTY

pyrayafoline-B was formulated as structure 186 which was confirmed by synthesis. 7-Acetylaminochromene (187), on reaction with 4-bromo2-methoxytoluene (lo), after refluxing in presence of copper pyridine and K,CO, for 43 hr, furnished the diphenylamine derivative 188. Hydrolysis and subsequent cyclization of 188 with Pd(OAc), in DMF furnished 0methylpyrayafoline-B (189). 6 . Pyrayufoline-C

Pyrayafoline-C [190, C,,H,,NO, (M+ 279.1258)] was obtained along with 186 (33). IR and UV data and the characteristic high-intensity mass spectral peak for the carbazolopyrillium ion at mlz 264 (M+ - 15) (6) showed it to be a phenolic carbazole derivative with a DMP system. This conclusion was also substantiated from the 'H-NMR spectrum, in which signals for a DMP system and H-4 (6 7.64), H-5 (6 7.63, d, J = 8.4 Hz), and H-l protons (6 6.79) appeared. On treatment with diazomethane it gave an 0methyl ether identical with synthetic pyrayafoline-A, showing pyrayafoline-C to be 190.

7 . Pyrayufoline-D Pyrayafoline-D (191, C,,H,,NO,, [aIDOO} was obtained from the same source as 186 and 190 (33) in the form of pale brown powder. The UV [A, 222, 238, 268 (sh), 296, 331, 342 nm] and IR (v,,, 3600, 3450, 3380 cm-') data and the high-intensity peak at mlz 265 showed it to be a phenolic pyranocarbazole derivative, which was also supported by 'HNMR data. Compared with pyrayafoline-C (190), the isolate showed an additional CH,CH,CH=C(CH,), side chain [a 1.75 (2H, m), 2. I5 (2H), 5.70 ( I H , t), 1.57 (3H, s), and 1.65 (3H, s)] in the pyran fragment. On methylation, it afforded a monomethyl ether. In NOE experiments with 0-methylpyrayafoline-D (192), the H-4 and H- 1 signals showed enhancement on irradiation of the aromatic methyl and methoxy groups, respectively. From these data, structure 191 was advanced for pyrayafoline-D.

4.

CHEMISTRY A N D BIOLOGY O F CARBAZOLE ALKALOIDS

301

8 . Pyrayufoline-E Pyrayafoline-E (193, C,,H,,NO,), obtained as a pale brown oil from M . euchrestifolia (28), displayed U V , IR, and 'H-NMR spectra similar to those of pyrafoline-B, suggesting the presence of a phenolic pyranocarbazole system. The mass spectrum showed the characteristic high-intensity peak for a carbazolopyrillium ion (6) at rnlz 264 (M+ - 83), proving the presence of the carbazolopyrillium ion, and a C, unit comprising CH,CH,CH=C(CH,),. 'H-NMR data also supported the presence of this six-carbon fragment [6 5.10 ( l H , t, J = 7.3 Hz), 2.13 (2H, m), 1.70 (2H), 1.65 and 1.57 (3H each)]. From the physical data the structure 193 has been proposed for pyrayafoline-E.

H2C

I

c H*C H=C'

CH3 'CH3

9. Mukonicine

Mukonicine [194, C20H,,N0, (M+ 323), mp 231-233"CI was obtained 226, 240, 300, 342 nm; log E from Murraya koenigii ( 6 1 ) . The U V (A, 4.70, 4.69, 4.59, 4.26) and IR data were close to those of koenimbine, suggesting the presence of a pyranocarbazole system, which was also supported by the characteristic high-intensity peak for the carbazolopyrillium ion at mlz 308 (6) (M+ - 15) as well as 'H-NMR signals for the DMP system [6 I .44 (6H, s), 5.65, 6.5 ( I H each, d, J = 10 Hz)]. It had a singlet for H-4 at 6 7.5, and H-5 appeared at 6 7.4 because of the methoxy at C6. Signals for the aromatic C-methyl at C-3 and two aromatic methoxy groups at 6 3.9 ( 6 H , s) were observed. Zinc dust distillation furnished 3methylcarbazole, and chromic acid oxidation furnished acetone arising from the DMP system. From these data, structure 194 has been suggested for mukonicine.

302

D. P. CHAKRABORTY

10. Glycomaurin

Glycomaurin (195, CIBH,,NO, mp 195-196"C), isolated in 1989 from Glycosmis mauritiana (32), showed a UV spectrum [A,, 215, 231, 262, 270 (sh), 284 (sh), 297 (sh), 312, 322, 378 nm with log E 4.18, 4.23, 3.90, 3.87,3.65,3.57,3.82,3.85,3.23]characteristic of a pyranocarbazole derivative. The base peak in the mass spectrum at m / z 248 showed the presence of a DMP system (6).Signals for H-4 (8 7.92) and for a DMP system were apparent in the 'H-NMR spectrum [8 1.46 (6H, s), 5.82 and 7.28 (2d, J = 9 Hz each)], and the isolate gave a dihydro derivative (56) on hydrogenation. From the 'H-NMR data, the structure of glycomaurin was advanced as 195, which was confirmed by synthesis of 195 along with the linear isomer 198. 6-Hydroxy-3-methylcarbazole (196) and 3-chloro-3methylbutyne (197), in the presence of the phase-transfer catalyst tetrabutylammonium bromide, furnished glycomaurin (195) and isoglycomaurin (198). Eustifoline-A (36) and 195 are identical. F?.

,

(197) H

H

(196)

11. Eustifoline-B

Eustifoline-B [195A, C,,H,,NO (M+ 33 I)] (36) showed a high-intensity mass fragment at mlz 248, showing it to be a pyranocarbazole, like 195, with an additional dimethylallyl unit. The structure of 195A was deduced from UV, IR, and 'H-NMR data as being similar to that of glycomaurin, except that one of the methyls in the pyran ring was extended by a dimethylallyl unit as in mahanimbine. 12. 7-Methoxymurrayacine 7-Methoxymurrayacine [199, CI9H,,O3(M+ 307.1208), mp 21 1-213"CI, 306, 354 nm; isolated from Murraya siamensis (24, showed UV (A,,

4.


303

(201)

log E 4.58, 4.19) and IR (Y,,,,, 3460, 1660, 1628, 1603, 1156 cm-I) data characteristic of a carbazole alkaloid. The IH-NMR spectrum showed signals for H-4 [6 8.23 (deshielded by an adjacent formyl group)], H-5 (6 7.97, d, J = 8.4 Hz), H-6 (6 6.83, dd, J = 8.4, 2.2 Hz), and H-8 protons (6 6.97, l H , d, J = 2.2 Hz), as well as signals for a DMP system [6 1.54 (6H, s), 6.90, 5.90 (1H each, J = 9.8 Hz)], an aldehyde proton (6 10.45, s), and an aromatic methoxy (6 3.85). The formyl group was placed at C3, and the DMP group was considered to be fused at the 2 : 1 position; the methoxy was placed at C-7 based on the coupling of H-8. A carbazolopyrillium ion at rnlz 292 (m+ - 15) was also observed. Thus, structure 199 was determined for 7-methoxymurrayacine, which was confirmed by I3C-NMR spectroscopy. 13. Isomahanine

Isomahanine 1200, C2,H2,N02 (M+ 347.1885), mp 184"C], isolated from M. koenigii (35),showed UV [A, 220, 238, 286, 294, 324, 338 nm; log E 4.51, 4.48 (sh), 4.29, 5.52, 3.68, 3.741 and IR spectra suggesting it to be a phenolic carbazole like mahanine (6). IH-NMR data showed signals for a DMP system in which a methyl has been extended by a dimethylallyl fragment, like that in mahanimbine. The mass fragment at mlz 264 (M+ - C,H,,) supports this. The resonance H-5 (6 7.56) was a singlet, and the H-4 and H-3 signals were ortho coupled, showing that the methyl was at C-6 and the phenolic group at C-7. The pyran unit was fused, as in mahanimbine at the 2 : 1 position. 14. Heptazolicine

Heptazolicine [201,C,,H,,N03 (M+ 295), mp 285"C], obtained from Clausena heptaphylla, was shown to be a phenolic carbazole with an

304

D. P. CHAKRABORTY

aldehyde function, judging from the UV and IR spectra. From 'H-NMR (201A), data it was shown to be a 3-formyl-2,2-dimethylpyranocarbazole and it was identified with cycloheptazoline by direct comparison ( 6 ) .

15. Pyrayaquinone-A Pyrayaquinone-A [202, C,,H,,NO, (M+ 293.1053), mp 22"C], a pyranocarbazoloquinone obtained from the stem bark of M . euchrestifolia (62), showed UV ,,A( 220 (sh), 252, 308 (sh), 460 nm] and IR (A,, 1660, 1640, 1010 cm-') spectra typical of a carbazoloquinone system. The 'H-NMR data (6 1.48, 6H, s, 5.78 and 6.4, 1H each, J = 10 Hz) and the mass spectral peak at mlz 278 (M+ - 15) showed the presence of a DMP system. The doublet at 6 6.46 and a 3 H signal at 6 2.16 for a vinylic methyl showed the presence of a substituted quinonoid system. The singlets for H-5 (6 7.79) and H-8 (6 6.83) demonstrated that the DMP system was fused to ring A of the carbazole system, with oxygen substitution at C-7. From these data, structure 202 was advanced for pyrayaquinone-A. 16. Pyrayaquinone-B

Pyrayaquinone-B [203, C,,H,,NO, (M+ 293.10531, mp 244"CI was isolated from M . euchrestifolia (62) along with pyrayaquinone-A (202). The UV and IR data were consistent with the presence of a 1,4-~arbazoloquinone system. A DMP system fused to the carbazoloquinone nucleus was indicated from the 'H-NMR data (6 1.48, 6H, s, 5.70 and 6.60, 1H each, J = 10 Hz) and the characteristic high-intensity mass spectral peak for the carbazolopyrilliurn ion (M+ 278). The signals for 1H at 6 6.44 and 3H for a methyl group at 6 2.14 with long-range coupling were reconcilied with the presence of a vinylic methyl at C-3 and no substitution at C-2. The ortho-coupled doublets for H-5 at 6 7.94 and H-6 at 6 6.87 (J = 9 Hz) showed that the DMP system was fused to ring A at C-7 and C-8, with oxygen at C-7. Therefore, pyrayaquinone-B is the angular isomer of pyrayaquinone-A. For structural confirmation, pyrayaquinone-A and -B have been synthesized using the method for the synthesis of murrayaquinone A (63). 7Amino- (204) and 5-Amino-2,2-dimethyl-2H-chromene (205) were condensed with methylbenzoquinone (71) to afford 2-(2,2-dimethyl-2ffchrornen-7-y1amino)- and 2-(2,2-dimethyl-2H-chromen-5-ylarnino)-5methyl- 1 ,Cbenzoquinones (206 and 207), respectively. Subsequent treatment of benzoquinones 206 and 207 with Pd(OAc), in acetic acid furnished pyrayaquinone-A (202) and pyrayaquinone-B (203).

4.


305

(20L)

17. Pyrayaquinone-C Pyrayaquinone-C [208, C,,H,,NO, (Mi361.1661), mp 222"CI was isolated, like pyrayaquinone-A (202) and pyrayaquinone-B (203), from M. euchrestifolia (20a-c). The UV and IR data were consistent with the presence of a 1,4-carbazoloquinonoid system, which was also indicated from the 'H-NMR signals for an aryl methyl at C-3 (6 2.15, d , J = 1.7 Hz) and the olefinic proton doublet at 6 6.45 ( l H , J = 1.7 Hz). The quinonoid carbazolopyrillium ion at mlz 278 (M+ - 83), the 'H-NMR signals (6 5.68, 6.63, l H , J = 10 Hz), the singlet for a methyl at 6 1.44, and other data suggested that one of the methyls of the DMP system was

306

D. P.

CHAKRABORTY

appended by a dimethylallyl unit like those in mahanimbine and related alkaloids. The ortho-coupled 'H-NMR signals for H-5and H-6 (6 7.94 and 6.80) suggested that the pyran ring was fused angularly as in pyrayaquinone-B. Consequently, pyrayaquinone-C was represented by 208. U

E. TETRACYCLIC ALKALOIDSFROM Streptomyces Eight antibiotics of the kinamycin type isolated from Streptomyces murayamaensis form an interesting group of antibiotic carbazole alkaloids (13). The detailed structural work on kinamycin-C forms the basis for structural determinations of the other alkaloids (64,65a,b). 1. Kinamycin-C Kinamycin-C (209, C,,H,,O,,N, (M+ 496), mp 150-153"C, [aID- 24" (CHCI,)}, isolated from S. murayamaensis, was considered to be a pheno-

W

C

H

O

/

/COCH3

\

OH

AN

CH AH

w

0 c

' I

?H H

I

0 '

\

OH

3

?

CN

I

bH

'CH3

4.


307

lic naphthaquinone derivative from UV spectral data and its red shift in alkali. 'H-NMR data of kinamycin-C showed the signals of one tertiary methyl (6 1.3, s), two alcoholic acetoxy groups (6 2.0-2.3), a hydroxyl group (6 2.57), a chelated phenolic group (6 12.0), two protons on vicinal carbons carrying acetoxy groups (6 5.4, 6.2), and three aromatic protons at 6 7.83, 7.5, and 7.6. The isolate yielded a diacetate (210,&,H,O,,N) and an 0-methyl derivative (211).The IR data of derivatives 210 and 211 showed that the phenolic hydroxyl group in 209 was peri to the quinonoid carbonyls. The presence of three acetyl groups in kinamycin was also mp 137-1 36°C). confirmed from its deacetylated product (212,C18H,407N2, From the 'H-NMR data of 212, the presence of an 8-hydroxynaphthaquinone fragment, two vicinal hydroxy groups, a tertiary methyl, and nitrile or isonitrile functions was ascertained. On sodium periodate oxidation, deacetylkinamycin furnished an aldehyde (213,C,,H ,,,06N2), which confirmed the presence of an alcoholic hydroxyl at C-1 and a tertiary methyl at C-2 in 212. By means of preparation of the isopropylidene derivative 214 of deacetylkinamycin-C (212)with acetone, the position of the tertiary hydroxyl at C-2 was ascertained. X-Ray crystallographic analysis of the bromobenzoate of kinamycin-C showed its structure to be 215. Hence, the structure of kinamycin-C was ascertained as 209. The presence of an N-cyano group in kinamycin-C was confirmed by hydrolysis of deacetylkinamycin-C 212 when ammonia was liberated; X-ray crystallography did not unambiguously ascertain the presence of a nitrile or isonitrile function in kinamycin-C.

2 . Kinamyein-A Kinamycin-A (216,C24H20010N2 (M+ 496), mp 139-142°C (dec.), [a]?$ -60" (CHCI,)} displayed UV, IR, and 'H-NMR data broadly similar to those of kinamycin-C, suggesting a structural similarity. Thus, kinamycinA has a hydroxyl group at C-4. The monoacetates of kinamycin-A and

.*- R2

CH3 OH

CN

6R1

308

D. P. CHAKRABORTY

kinamycin-C were identical, showing the isolate to be 4-deacetylkinamycin C. Consequently, the structure of kinamycin-A was advanced as 216. 3. Kinamycin-B

Kinamycin B (217, C,,H,,O,N, (M+ 412), mp 190-193°C (dec.), [a15 -48" (CHCI,)} had physical properties (IR, UV, and 'H-NMR) similar to those of kinamycin-A, showing the two carbonyl functions to be hydrogen bonded. Tetraacetylkinamycin-B was identical with the diacetate of kinamycin-C. From these and other data, the structure of kinamycin-B was advanced as 217. 4 . Kinamycin-D

Kinamycin-D (218, C,,H,,O,N, (M+ 452), mp 170-175°C (dec.), [a]% -37" (CHCl,)} yielded IR, UV, and IH-NMR data similar to those of kinamycin-A, showing it to have a hydroxyl at the 4 position. On acetylation kinamycin-D furnished deacetylkinamycin-C, proving its structure to be 218.

5 . Prekinamycin Prekinamycin [219, C,,H,,N,O,, mp 300°C (dec.)], obtained from Strep254, 288.4, 342, tomyces murayamaensis (66,67), showed UV (A,,

(219)

n

4.


309

574 nm; E 5500, 21,700, 5770, 37,700) and IR data characteristic of a carbazole system with a hydroxyl group chelated to a quinonoid function and is thus related to the kinamycins. In the 'H-NMR spectrum, the signals for two meta-coupled H-1 and H-3 protons (6 6.60, 6.69, 1H each, d , J = 1.5 Hz), three aromatic protons at H-5', H-6', and H-7', and an aromatic methyl group (6 2.29) were readily discernible. Two proton signals at 6 11.60 and 12.32 disappeared in the diacetate {C,,H,,N,O, (M+ 402.239), mp >300"C (dec.)]. In the I3C-NMR spectrum of the diacetate, signals for two quinonoid carbonyls (6 174.4 and 192.45), two ester carbonyls (6 170.28 and 170.64), and a cyanamide function (6 83.71) were detected. These data, together with I3C-NMRdata of a sample obtained biosynthetically through feeding experiments, supported the structure of prekinamycin as 219. 6. Ketoanhydrokinamycin

Ketoanhydrokinamycin [220, CI8HIONZO6 (M+ + H + 351), mp 300°C (dec.)] was isolated by Seaton and Gould (67). The U V and IR spectra were similar to those of kinamycins. The 'H-NMR data of 220 showed the presence of two hydroxyls (6 5.94 and 12.06), one of which was a hydrogen-bonded phenolic hydroxyl (6 12.06), but no acetate signals as in the other kinamycins. I3C-NMR data indicated the presence of 1,4quinonoid system (6 183.67, 180.85) and a conjugated carbonyl function (6 188.62). The coupling (2 Hz) of H-3 and H-4 (6 3.89 and 5.34) showed the regiochemistry of the hydrogens. The signal at 6 5.34 showed coupling to a hydroxyl at 6 5.94. The long-range heteronuclear shift correlation (HETCOR) spectrum showed the coupling of the methyl hydrogens at 6 1.53 and the carbonyl at 6 188.62, suggesting the presence of the carbonyl at C-1 of ring C. In NOE experiments, enhancement of resonances at 6 3.89 and 5.34 by irradiation of the methyl group confirmed the positions of H-3 and H-4 in ring C. These data permitted the formulation of ketoanhydrokinamycin as 220.

7. Kinamycin-E Kinamycin-E [221, C,oH,,N,O, (M+ 412.0906), mp >200"C (dec.)] was obtained from a culture extract of S. murayamaensis (67). From the U V (A, 255.6, 277, 295, 408 nm) and IR spectra, it was considered to have a kinamycin-C chromophore, and from the 'H-NMR spectrum it was inferred that the isolate had a kinamycin-D type acetylation pattern. Treatment of kinamycin-D with methanolic potassium carbonate gave a small amount of kinamycin-E, showing the latter to have structure 221.

310

D . P. CHAKRABORTY

8. Deacetylkinamycin-C. Kinamycin-F (212), also isolated from S . murayamaensis (67), was found to be identical with deacetylkinamycin-C based on physical data. Compound 212 was obtained by hydrolysis of kinamycin-D (218).

F. SYNTHESIS AND TRANSFORMATION OF TETRACYCLIC ALKALOIDS 1 . Synthesis

The novelty of the structures of the antibiotics of the kinamycin group has attracted the attention of synthetic organic chemists, and several strategies have been developed to build up the tetracyclic system or proposed intermediates in the biogenesis of kinamycin. Palladium-catalyzed

CONH-t- BU (222)

(224 1

(223)

2 steps

[Me301 BFL OCH3 OH

0 (226) NH2OH in MeOH+ Demethylation BBr3 in C H C l 2 a t -70' C

OH OH

0 (225)

4.


311

coupling of 2-bromojuglone (222)with the stannane 223 furnished the intermediate 224, which was transformed in two steps to 225. Treatment of 225 with [(Me,O)+]BF,- in T H F at 23°C gave 226, which, on treatment with NH,OH in methanol and subsequent demethylation, furnished the naphthaquinonoid quinolone 227 considered to be an intermediate in the biosynthesis of prekinamycin (219)(69). In another approach to the synthesis of prekinamycin (68),the entire skeletal unit of prekinamycin was obtained except for the cyano group of the carbazole fragment. Bromonaphthaquinone (228),on annelation with cyclic N-benzylaminoketone (229),furnished in moderate yield (36-50%) tetrahydrobenzo[b]carbazole-l,6, I I-trione (230),which, in refluxing dioxane in the presence of DDQ, gave the benzo[b]carbazole (231),having a carbon framework identical to that prekinamycin, except for the cyano

(231

(230)

substitution at the carbazole nitrogen. A simple approach to the benzo[b]carbazoloquinone skeleton (232) of the kinamycins has also been worked out through the oxidative cyclization of 2-benzoylindole containing a benzylic alcohol in the orrho position (233)with tetra-n-butylammonium perruthenate (TBAP) (70).

& z & N

\

O (232)

H

N

/

O (233)

H

312

D . P. CHAKRABORTY

The synthesis of norgirinimbine (235)and its linear isomer (236)provides an illustration of the thermal insertion of a C, unit into a carbazole skeleton. 2-Hydroxycarbazole-3-carboxylic acid (234), when heated at 145°C in the presence of SbCl,, provided, after workup in three steps, norgirinirnbine and its linear isomer as the end products (13,71).

+ H (236)

Pate1 has reported (72-74) some interesting synthetic studies in relation to analogs of girinimbine and mahanimbine, which have been reviewed previously (13). Synthesis of normahanimbine (237) and regioisomer 238 from 2-hydroxycarbazole (239), under conditions of citral condensation (13), show that the reaction is regioselective, not regiospecific (75).

.

~itral

Py r c f l u x

OH

2. Transformations a. Cyclomer Formation in Muhanimbine. Some results on the formation of cyclomers of mahanimbine have been enumerated previously (6), and further results are described here. Mahanimbine (240) has been thermally transformed into murrayazoline (241) and rnurrayazolidine (242). On prolonged heating only murrayazoline is obtained (i3,76). When passed

4.

-a


313

qcH2 (2.40)

\

C H 2 CH=c 'CH3 /CH3

(2.41)

3

through a column of Dowex 50-X8 resin (H form), mahanimbine furnishes racemic murrayazolidine (77). +

b. Transformation of Optical Properties. In isooctane solution, mahanimbine (240) and normahanimbine (237) undergo racemization at 90°C when kept in the dark (77). On sitting in ethanolic solution at room temperature (37"C), mahanimbine undergoes racemization and subsequent optical inversion (+45" to -24.8") when kept for 6 days. The reaction is catalyzed by hydrochloric acid. In chloroform solution the compound does not undergo inversion. The racemization of mahanimbine and its congener, as well as the inversion of 240, could be explained as arising from enone-chromene transformation (13).

c. Photochemical Transformation of Girinimbine and Mahanimbine. Studies on the photochemical transformation of the tetracyclic

(2.43)

H (2.4.4)

314

D.

P. CHAKRABORTY

carbazoles girinimbine (181) and mahanimbine (240) have been reported to result in the expansion of the pyran ring (78). The transformation has been perceived to proceed through an 0-quinolide intermediate and subsequent 1,4-shift and cyclization. The nitrogen lone pair probably participates in the ring expansion, as N-sulfonyl derivatives of the alkaloids do not undergo the transformation.

G. HEXACYCLIC ALKALOIDS

FROM

HIGHER PLANTS

The penta- and hexacyclic carbazole alkaloids of higher plants are derived from a tricyclic carbazole unit and a monoterpene unit. Thus, murrayazolidine, murrayazoline, and related compounds are derived from mahanimbine. 1 . Murrayzoline

(+)-Murrayazoline (241, C,,H2,N0 (M+ 3 3 3 , mp 276-278"C, [ale +2.25" (CHCI,)} was isolated from Murruya euchrestfolia (29).The U V , IR, and IH-NMR spectra showed it to be identical with murrayazoline, except for the optical activity. Thus, compound 241 has been considered to be an optical antipode of murrayazoline. 2. Murrayazolinol Murrayazolinol(245, C,,H,,NO, (M+ 347), mp 290"C, [ a ] ,0" (CHCI,)}, isolated from Murruya koenigii (79), showed UV data (A,,, 248, 365, 305 nm with log ~4.85,4.32,4.40)indicating the presence of a 2-oxygenated carbazole system. The 'H-NMR data were similar to those of murrayazoline, except for an additional hydroxyl group and a carbinyl hydrogen signal at 6 3.8. By comparison of the mass spectral data and the benzylic proton signals of murrayazolinine (245A) (6 3.65) (6) and isomurrayazoline (6 3.08) (13) with those of murrayazoline (6 3.83) and consideration of the spectral pattern of the carbinyl hydrogen signal at 6 3.80, the hydroxyl group was placed on a carbon adjacent to the oxygen linked to the carbon atom of the pyran ring, and structure 245 was advanced for murrayazolinol.

4. H.

CHEMISTRY A N D BIOLOGY OF CARBAZOLE ALKALOIDS PENTA- A N D

315

HEXACYCLIC ALKALOIDS FROM Aspergillus

1 . Tubingensin-A

From the sclerotia of Aspergillus tubingenesis was isolated tubingensinA (246, C,,H,,NO (M+ 401.2698), mp 95-98"C, [aID13.6" (CHCI,)} (80). The UV spectrum suggested acarbazole chromophore (A, 218,239,262, 302, 326, 341 nm with E 14,900, 18,200, 6930, 6780, 480, 480), and 'HNMR data indicated the presence of an isolated four-spin system, showing that there was no substitution in ring A . The signals for H-1 (6 7.92) and H-4 (6 7.11) showed that C-2 and C-3 were substituted, which was also supported through insensitive nuclei enhanced by polarization transfer (INEPT) correlation data. The attachment of C-10 to an sp2 center was inferred from the downfield shifts of two of the C-10 protons (6 2.99,2.88, br dd). The six-carbon chain attached to C-13 was evident from the 'HNMR data and was also supported from the mass spectral peak at mlz 318 (M+ - 83, base peak). From the detailed INEPT studies, NMR correlation studies, and biogenetic considerations, structure 246 was proposed.

-4 ..

H

H

The stereochemistry of tubingensin-A (246)follows from NOE spectroscopy (NOESY) correlation studies. The equatorial disposition of H-14 is in accord with a trans-diaxial coupling between H-14 and the neighboring proton. The gauche relationship between C-18 and C-19 is inferred from correlation studies, and the cis orientation of H-17 and C-1 1 is consistent with the cross-peak correlating the axial proton at C- 10 with a signal centred at 6 1.74 (H-17). The methyl groups have also been considered to be cis, and the substituents at C-12 and C-17 and their relative disposi-

3 16

D. P. CHAKRABORTY

tions with respect to C-1 1 and C-14 were deduced from additional correlations.

2 . Tubingensin-B Tubingensin-B (247, C,,H,,NO (Mi 401.2733), mp 152- 154°C [ a ]+ 6.7" (CHCI,)} was isolated along with tubingensin-A (81). It displayed U V data (A, 218,237, 260,299, 325,338 nm with E 17,200,25,500, 10,100, 10,100, 2200, 6700) suggestive of a carbazole derivative. The base peak in the mass spectrum at mlz 218 (M+ - 183) represented the tetracyclic ring with a 9H carbazole system arising from loss of a C,2H2,0unit from the molecule. IH-NMR data showed that ring A was unsubstituted, and the broad singlets for H-4 (6 8.05) and H-1 (6 7.32) showed that the C-2 and C-3 positions were substituted. The spin systems were also established by homonuclear decoupling and 'H-IH COSY experiments. Selective INEPT and HETCOR experiments were used for precise assignments of I3C-NMR signals. From these data, especially those obtained from selective INEPT experiments and from various other correlations, structure 247 was assigned to tubingensin-B. From the similarity of the W-NMR data of nominine (248) and tubingensin-A (246), together with the results of NOESY experiments, the relative stereochemistry of tubingensin-B was deduced. In consideration of the spatial requirements of the rings, the isopropyl group at C-10 was considered to be cis to C-14. 3 . Aflavazole

Aflavazole [249, C,,H,,NO, (M+ 417.2694), mp 156-16o"C], isolated 219, 243, from the sclerotia of Aspergillus j a m s (821, showed UV (A,, 263, 297, 327, 341 nm, with E 15,300, 17,300, 7500, 7600, 1300, 1600) and IR data for a carbazole derivative with hydroxyl groups. In consideration of its molecular formula, the degrees of unsaturation, the nature of the oxygen functions, and the presence of 12 aromatic carbazole carbons, as evidenced from the I3C-NMR spectrum, it was suggested that aflavazole is a hexacyclic base.

4.


317

The evidence for a 2,3,4-trisubstituted carbazole skeleton came from 'HNMR decoupling experiments and COSY data, together with the results of INEPT experiments. By analogy with the physical data of the aflavanine skeleton (250),the skeletal system for rings D and E and the methyl at C-2 were assigned. The direct linkage of C-13 with the aromatic ring was deduced from the correlation data, and the downfield shift of H-13 (8 4.18 ppm), was attributed to the deshielding effect of the aromatic ring. The aromatic methyl signal was correlated with three aromatic carbon signals (8 126.60, 135.13, 110.25 for C-3, C-2, C-l), confirming its position meta to C-4 and ortho to C-1. From IH-NMR and 13C-NMR data and INEPT and NOESY correlations, structure 249 was assigned to alfavazole. The relative stereochemistry was assigned by analogy with the stereochemistry of aflavanine (250), which has also been supported by NOESY data. I. HEXA-A N D OCTACYCLIC INDOLOCARBAZOLES

Staurosporine (251),the first member of the novel bioactive indolocarbazole* alkaloids, was isolated by Omura e f a/. in 1977 (83,84) from a member of the genus Streptomyces. In 1980 arcyriaflavins (252,253) containing the indolocarbazole skeleton were isolated from Arcyria deni4data (85). They were considered primarily indolic pigments. Biosynthetic work (86) on the rebeccamycin (e.g., 254) (86-88) and staurosporine (251)(89) led to the understanding that these alkaloids, like the carbazomycins of Streptouerticilfium ehimense (13), originate from tryptophan, though the nitrogen of the phthalimide unit does not come from tryptophan. The indolocarbazole skeleton present in these alkaloids has been classified with carbazoles (21b);hence, this group of bioactive indolocarbazoles is included here.

I . Arcyriajlauin-B and -C Arcyriaflavin-B (252, C,,H 13N303,mp 35OOC) and arcyriaflavin-C (253, C,,H,,N,O,) were isolated along with the indolic pigments arcyriarubin B (255)and arcyriarubin C (256)from the fruiting bodies of the slime mold Arcyria denudata (85). The structures of the indolocarbazoles 252 and 253 were based on structural studies of the associated indolic pigments 255 and 256. The maleimide/phthalimide moiety in the compounds was detected from the IR bands at around 1750 and 1705 cm-I, and the I3C* In consideration of the Chemical Abstracts conventions for the tricyclic carbazole system, the numbering of carbon atoms in the aglycone fragments of the indolocarbazoles has been modified from that reported by the respective authors.

318

D. P. CHAKRABORTY O+N

H

(252) R = H ( 2 5 3 ) R = OH

R

HO

NMR signals at 6 175.3 and 129.2 of the indolic pigments acryriarubin-B (255) and -C (256) supported such assignments. The absence of the 2,2' signals present in the 'H-NMR spectra of 255 and 256 from those of acryriaflavin-B and -C showed that the linkage of the indolic fragments in 252 and 253 was through the 2- and 2'- positions in the indolocarbazole. The UV spectra of arcyriaflavin-B and -C were similar to those of staurosporine, showing the presence of the indolocarbazole chromophore. The signals of H-5 and H-13 (6 8.93) in the 'H-NMR spectra of the compounds showed that the maleimide fragment was fused to the carbazole skeleton at the 3,4 positions. These structures have been confirmed by transforma-

H ~ S O ~ ( 2 5 2 ) ( R = H)

( 2 5 3 ) ( R = OH) H (255) R - H ;

H (256) R = O H

4.


319

tion of arcyriarubin-B and -C to arcyriaflavin-B and -C, respectively, with H,SO,. Synthesis of arcryiaflavin-B (252) was accomplished by Hughes and Raphael as follows (90). The phosphonium bromide 257 was converted to 258 with nitrosocinnamaldehyde to yield a mixture of stereoisomeric dienes, which was converted to pure E,E-diene by room temperature treatment with iodine in toluene. Heating with neat maleimide gave a Diels-Alder adduct (259), which, on DDQ treatment, afforded substituted terphenyl 260. Deoxygenation with triphenyl phosphonium in refluxing collidine for 40 hr yielded the double nitrene insertion product 261. On demethylation with pyridine hydrochloride arcyriaflavin-B (252) was obtained.

2. Protein Kinase Inhibitor K-252c

Alkaloid K-252c [262, C,oH,3N30(M+ 31 1.1079), mp >300°Cl, a protein kinase inhibitor, was isolated from Nocardiopsis sp. K-290 (91,92). The

320

D. P. CHAKRABORTY

UV spectrum [A, 230, 238, 246, 257, 287, 320, 331, 341, 358 nm, with E 37,000, 34,000, 28,000 (sh), 29,000 (sh), 86,000, 16,000, 20,000, 16,000, 1 1001showed the presence of an indolocarbazole chromophore like staurosporine. The 'H-NMR spectrum displayed the NH protons at 6 1 1.46 and 1 I .38, a secondary amide (6 8.49), and signals similar to those K-252a (K252a and K-252b are discussed below), which showed that the indole nitrogen atoms were unsubstituted. K-252c was also obtained from K252a by drastic hydrolysis, showing it to be the aglycone of K-252a. Consequently, structure 262 was assigned to K-252c.

(262) R = H (263 ) R =

HO

OH

3. Protein Kinase Inhibitor K-252d Alkaloid K-252d (263, C,,H,,N,O,, mp 240-245°C (dec.), [a],, + 35" (CH,OH)} (91,92)displayed physical properties similar to those of K-252c and K-252a. It produced an 'H-NMR signal for one NH (6 11.68) and a secondary amide signal (6 8.54), showing that, unlike K-252c, one of the NH nitrogens was substituted, suggesting the incorporation of a sugar moiety at the carbazole nitrogen. From the high-resolution electron-impact (EI) mass spectrum, the composition of the sugar moiety was found to be C&,404, and on hydrolysis of K-252d rhamnose was isolated. From detailed considerations of the 'H- and ' T - N M R data of the compound, the structure of K-252d (263) was found to be 9-N-(a-~-rhamnopyranose)K-252c, where the rhamnopyranosyl moiety has a 'C4 configuration. 4 . Rebeccamycin

+

Rebeccamycin (254, C,,H,,N,O, (M+ 1, 570, mp 326-330°C (dec.), [aID 131" (THF)}, obtained from (93)Nocardia aerocofonigenes(87,88),

+

4.

CHEMISTRY A N D BIOLOGY O F CARBAZOLE A L K A L O I D S

321

showed the presence of hydroxyl and cyclic imide functions (v,,, 3418, 3355, 1752 cm-I). The IV data showed maxima at 238 and 3 14 nm, besides shoulders at 256,293,362, 390 nm. The IH-NMR data showed signals for an amide N H (6 11.37) and an indole N H (6 10.30), in addition to signals for aromatic protons and sugar fragments. In rebeccamycin the aromatic protons H-5 and H-13 are both deshielded owing to the anisotropic deshielding effect of the phthalimide function, unlike staurosporine where the lactam function deshields only the ortho H-5 proton. Rebeccamycin U

& \

CI

N

N H

(266)

c1

322

D . P. CHAKRABORTY

afforded a tetraacetate which showed a UV spectrum similar to that of staurosporine. In consideration of the 'H-NMR signals of the glycosidic protons and the proton signals of the aglycone moiety, a 4-0-methyl glycosidic linkage with the aglycone was indicated. The chemical shift of H-I' in both rebeccamycin and its acetate showed that the sugar residue was either a C- or N-glycoside. The structure of rebeccamycin was deduced from X-ray crystallographic studies and its absolute configuration from synthesis (87).7-Chloroindole (264),on treatment at room temperature with MeMgI and I-benzyloxymethyl-2,3-dibromomaleimide(265) in benzene containing small amount of hexamethylphosphoramide (HMPA), furnished the desired 2 : I adduct 266 and a 1 : I by-product. The 2 : 1 adduct was photocyclized to 267 in the presence of iodine. In a one-pot method, cyclization and glycosidation were effected by reacting 264 and 265 in the presence of Ag,O in benzene, probably via thermal cyclization to 267 of the intermediate triene system 266. Subsequent glycosidation with 1-bromo-2,3,6-tri-0-acetyl-4-O-methylglucose (268) in refluxing benzene gave 269. The benzyloxymethyl group was removed by hydrogenation and the acetyl groups by ammonolysis, by which rebeccamycin (254) was obtained in 95% yield. Because the sugar moiety was prepared from D-glucose, the absolute configuration was determined to be the same as D-glucose. A shorter route to the synthesis of the aglycone and thus to a rebeccamycin was found. 7,7-Dichlorobisindigo (270) on Wolff-Kishner reduction and acetylation furnished (271) monoacetyl bisindole which, on heating with N-benzoyloxymethylmaleimide in a sealed tube at IO5"C for 8 days afforded the aglycone. The reaction probably involves an initial Diels-Alder reaction followed by loss of acetic acid and subsequent dehydration.

4.


323

5 . Antitumor Alkaloids AT 2433-Al, AT 2433-A2, AT 2433-B1, and AT 2433-B2 Antitumor compounds AT 2433-A1 [272), C3,H,,N4O9C1 (M+ 678)], AT 2433-A2 [273, C33H3,N40&1 (M+ 664)], AT 2433-B1[274, C34H36NdO9 (M' 64411, and AT 2433-B2 [275, C,,H3,N40, (Mi 630)] were obtained as yellow solids from Actinomaduru melliaura sp. nov. (SCC 1655) (91). Because AT 2433-A1 was obtained in large quantity, structural determinations of compounds 272-275 were based primarily on the reaction profile and degradation sequence of AT 2433-A1 (94).

(272 1 (273) (274) (275)

AT AT AT AT

2433-A1 2133-A2 2L33-81 2L33-82

R = CI 3 R'= H3C R = C I , R'=H R = H , R'=CH3 R = H 9 R'=H

AT 2433-A1 showed a U V spectrum (A,, 200, 235, 283, 316, 395 nm, with log E 30,781, 39,934, 34,307, 45,562, 3865) similar to that of rebeccamycin, suggesting the presence of an indolocarbazole chromophore. The IR spectrum showed the presence of hydroxyl and cyclic imide functions (v,,, 3120, 3365, 1750, 1962 cm-I). Unlike rebeccamycin, the imide NH signal (6 3.25) in the 'H-NMR spectrum of AT 2431-A1 was replaced by an N-CH, signal, indicating methyl substitution at the imide NH. Like rebeccamycin, both H-5 and H-13 were anisotropically deshielded (6 9.27 and 9.18) owing to the imide carbonyl functionalities. The elemental composition of the compound was determined from the high-resolution flamedetection (FD) mass spectrum, in which isotopic clusters for molecular ions indicated the presence of one chlorine atom. Important information was also obtained from the EI mass spectrum of the volatile tetracetate. The presence of a 4-methoxyglucopyranoside fragment was ascertained from the 'H-and 13C-NMRdata of A T 2433-A). The 'H-NMR sjgnals for

324

D.

P. CHAKRABORTY

the C-4' rnethoxy (6 3.68) and the C-I' anomeric rnethine protons (6 6.91) as well as the 13C absorptions of C-I' or C-5' and 4'-OCH, were very close to those of rebeccarnycin. The downfield shift of the C-6' absorption to 6 66.00 pprn as compared with rebeccarnycin suggested further substitution. The downfield shift of the anomeric proton of AT 2433-A1 as cornpared with the dechloro congeners showed the proximity of H-I' to an electronegative chlorine. Further, from the "C-NMR signal of the anomeric carbon, a N-C glycosidic bond was located at N-9. The triplet arising from the 6'-OH proton in rebeccamycin was absent in AT 2433A l , showing the linkage of the aminosugar at that position. Studies on the methanolic hydrolysis products of the carbazole provided information on the structure of the arninosugar in AT 2433-A1. The 'HNMR spectrum at I 10°C* of the 3,4-di-4-brornobenzoate of methyl 2,4dideoxy-4-N-rnethylaminopyranoside provided information regarding the a configuration at C-1" and an equatorial substitution of the pyranoside at C-3". The CD spectrum of the derivative showed that the chilarity of 3,4-dibromobenzoate is 2 - ~ - t h r e o . The CD spectrum of AT 2433-A1 was superirnposable with that of rebeccamycin, showing identical chilarity for the two compounds and thereby confirming the absolute structure of AT 2433-A I (272). Structures of AT 2433-A2 (273), AT 2433-Bl (274), and AT 2433-B2 (275) have been deduced from the 'H-NMR spectra and other physical data. In the case of AT 2433-A2, the aglycone part was identical with that of AT 2433-A I . In the case of AT-2433-B1 (274) and AT-2433-B2 (275), the aglycone parts were found to be dechlorinated congeners, resulting in shifts in the proton and carbon spectra of the respective compounds. The arninosugar fragments of 272 and 274 were identical, whereas those of 273 and 275 were N-demethylated. The chilarity of the antitumor compounds is identical to that of rebeccamycin. 6. Stuurosporinr

Staurosporine (251, CZRH26N403 (M+ 466), rnp 270°C (dec.), [ a ] + 35.0" (MeOH)} was isolated from Streptomyces stuurosporeus Anaya, Takahashi, and Ornura sp. nov. (83).The U V (h,,,243, 263 (sh), 292, 322 (sh), 335, 356, 372 nrn] and IR (vmax 3200, 3500 crn-I) spectra showed the presence of hydroxyl and arnine groups, and an aromatic system. The structure and stereochemistry of the isolate were established by X-ray crystallographic analysis of the methanol solvate (84).Complete and unam-

* Owing to a rotational barrier about the amide bond, a highly complex spectrum is observed below 1 I O T .

4. CHEMISTRY A N D BIOLOGY OF CARBAZOLE ALKALOIDS

325

biguous assignments of the IH- and 13C-NMRspectra of 251 have been accomplished (942). There have been several attempts to synthesize staurosporine aglycone by various methods, as detailed below. The staurosporine aglycone was prepared from tryptamine and p-indoloacetic acid in two consecutive cyclization reactions (95). The starting amide 276 was prepared from tryptamine and the appropriate acid chloride. DDQ oxidation of the amide in a mixture of water and THF yielded the diketo compounds 277, which on selective reduction with NaBH, gave rise to the hydroxyketone 278. On acetylation in the presence of 4-dimethylaminopyridine (DMAP), the cyclized pentaacetate 279 was obtained. Reduction of 279 with TiCI, in aqueous acetone afforded the lactam 280, which on deacetylation with NaHCO, in aqueous methanol and subsequent irradiation furnished the aglycone of staurosporine. In another method (96),dibromomaleimide was N-benzylated to afford 280A, which on treatment with indolylmagnesium bromide gave 280B. Oxidation with p-toluene sulfonic acid/DDQ provided a skeleton related to the staurosporine alkaloids (280C). Magnus and Sear (97) reported the synthesis of the aglycone of staurosporinone using indole-2,3-quinodimethanemethodology. Tryptamine was converted to its phthalimide derivative 281, and the indole nitrogen was protected by treatment with p-methoxybenzene sulfonyl chloride with NaH and DMF to give the sulfonyl derivative 282. Subsequent formylation with 2,2-dichloromethyl methyl ether-titanium tetrachloride at 35°C gave 283, which, on condensation with 2-aminostyrene, afforded the imine 284. The 2,3-quinodimethane intermediate generated in the usual way yielded the pentacyclic carbazole 285, along with other reaction products.Dehydrogenation of 285 (DDQ-toluene reflux) gave the indolocarbazole 286. The phthalimide protecting group was selectively removed by treatment of 286 with hydrazine hydrate in THF at 20°C to afford 287. Treatment

NaBHL redn.

&Cm I

\

-

1

\

I

1

N

N H

N

N Ac

i-,s’Bn H

Ac

H (278)

(279) I

Ticl3

H

& \

Ac N

H

NaHC03

Ac

% +*

(280)

/

\

‘h

D D8, 7

Ph H/A TsO H

4. CHEMISTRY

A N D BIOLOGY OF CARBAZOLE ALKALOIDS

mR,

327

f NPht

R

(284)

of 287 with phosgene in dichloromethane followed by TiCl, (0°C) gave the hexacyclic carbazole 288. The p-MeOC,H,SO, group was selectively removed using LiNH,-THF to yield 289. With KOH/glyme, 289 gave 290, thereby offering the potential to attach a carbohydrate substrate regiospecifically.

= H

In the course of the synthesis of arcyriaflavin-B, Hughes and Raphael (90) also reported an approach to the synthesis of staurosporine starting with 1,4-(dinitrophenyl)butadiene and N-benzylmaleimide. The same series of reactions as used in the case of arcyriaflavin provided the

328

D. P. CHAKRABORTY

(2911

(292)

N-benzylmaleimide derivative 291, which on Clemenson reduction gave the lactam 292, which might be employed as an intermediate in the synthesis of staurosporine. 7. Tan-1030A

Tan-l030A (293, C2,H2,N4O4 [(M + H)+ 4671, mp 290-295°C (dec.)}, obtained from Streptomyces sp. C-71799, was isolated by Tanida et al. (98). The UV (A,, 233, 244, 263 (sh), 275 (sh), 289, 359 (sh), 333, 352, 369 nm, with E 29,400,28,000,31,300,4200,71,000,13,400,17,700, 12,100, 13,4001 and IR spectra (v,,, 3430, 1680 cm-') showed that it was an indolocarbazole derivative with NH, OH, and amide functions, like staurosporine. IH-NMR and I3C-NMR data were close to those of staurosporine and supported the presence of an amide group, nineteen s p 2 carbons, one quaternary carbon, two methines, two methylenes, one methyl, and one

(295)

R = NHCOCHj9R1 = R 2 = H

4.


329

methoxy. On hydrogenation, Tan- 1030A gave an amine (294, C,,H2,N403 ( M + 452), [aID +90.4" (CHCI,)}, which was acetylated to the N-acetyl ( M + 474)]. The complete structure of this derivative 295 [C,,H,,N,O, bioactive substance was finally ascertained by NMR (99). 'H-'H COSY provided information as to the partial structures, which were further explained and clarified using IH-13C COSY and correlation spectroscopy via long-range couplings (COLOC). For COLOC experiments, the optimization was obtained using refocused INEPT experiments. From the results of COLOC experiments, further expansion of the partial structure was obtained that substantiated the proposal that it had a y-lactam, a 1,2-disubstituted benzene, and another 1,2-disubstituted benzene fragment with two quaternary carbons. Tan- 1030A (293) had a fragment containing methoxymethine carbons as NMR spectroscopy showed the methoxy carbon (6 58.29) coupled with a methine (H-4', 6 4.73) and vice versa. From the long-range coupling data, the presence of an oxime function was detected. The oxime carbon was correlated with the methine protons H-4' and H-l', which showed that the CHCH, group and the methoxymethine group were connected through the oxime group. The data were in agreement with the fact that the CHCH, group was part of a six-membered ring moiety carrying the oxime function. The downfield shifts of the methine (C-l', 6 82.17) and quaternary carbons (C-5', 6 98.16) show that the two carbons are bonded to heteroatoms (N, N, 0). From the data obtained in COLOC experiments with J = 12.5 Hz, it was shown how ten of the thirteen quaternary carbons were connected. Two of the remaining three carbons (6 114.98, 114.02, and 128.03) were observed in the refocused INEPT experiments when the delay was set at 60 msec. From the long-range coupling experiments, two quaternary carbons (C-4a, 6 114.98, and C-3, 6 114.02) were found to be coupled to H-5 and H-13, respectively. From these data, the two quaternary carbons C-14a and C-9a were considered to be bonded to two nitrogen atoms. For the placement of the lactam function, the two disubstituted benzenoid fragments, and the six-membered cyclic fragments carrying the oxime function, NOE experiments were helpful. On irradiation of the methylene protons, enhancement of the amide NH proton (H-16) and H-13 were observed. In addition, irradiation of the methyl (H-6', 6 2.47) and the methine (H-l', 6 7.04) groups led to enhancement of H-10 and H-8 signals, which supported a structure in which the lactam function, the disubstituted benzene ring, the hexacyclic sugar fragment, and another aromatic ring were connected in order. On irradiation of the oxime proton (6 10.45), enhancement of the signals for the methoxy group (6 3.3) and the methyl proton (H-6', 6 2.47) were observed, from which the stereochemistry of

330

D. P. CHAKRABORTY

the oxime group was ascertained. These data led to the formulation of Tan-1030A as 293. 8. Tan-999

Tan-999 (296, C,,H,,N,O, (M+ 496), mp 221°C (dec.), [aID+42" (DMF)} was isolated along with Tan-1030A from Nocardiopsis dassonuillei (98,99). Like Tan-1030A and staurosporine, it showed IR and UV data suggesting the presence of an indolocarbazole chromophore with a lactam functionality. The 'H-NMR spectrum of Tan-999 was similar to that of staurosporine except for the presence of an additional methoxy group, resulting in the presence of a 1,2,4-trisubstituted benzene ring instead of a 1,2disubstituted benzene ring. From the results of 'H-lH COSY and 'H-I3C COSY, refocused INEPT and COLOC experiments were carried out to determine the position of the methoxy substitutent. In the COLOC spectrum (J = 4.2 Hz), a quaternary carbon was correlated with the methoxy protons (6 3.95) and the aromatic proton H-13. A NOESY experiment showed a cross-peak between the methoxy protons and two aromatic protons (H-12 and H-10). NOE enhancement was also observed between the aromatic proton H-10 and the methyl protons H-6'. These data showed that the aromatic methoxy group was located at C-l 1. The NOESY spectrum also showed the correlation of H-14 and H-13 with the signals of H-l'and H-8. From these data, structure 296 was advanced for Tan-999 (99). 9. Protein Kinase C Inhibitors K-252a and K-2526

Structures of the hexacyclic protein kinase C inhibitors K-252c (262) and K-252d (263) are discussed above. The octacyclic alkaloids K-252a and K-252b are treated here (92,100). Alkaloid K-252a (297, C,,H21N205(M+ 467), mp 262-273"C, [a]-23" (CHCI,)} was isolated from Nocardiopsis sp. K-252 and K-290. The UV and IR spectra of the compound showed it to be an indolocarbazole with NH, OH, ester, and amide functions. 'H-NMR and I3C-NMRdata further showed that it possessed one secondary amide group, one methoxycarbony1 group, one tertiary hydroxyl, eighteen sp2 carbons, one quaternary carbon, one methine, two methylenes and one methyl. The presence of the following structural moieties was inferred from different decoupling experiments: two 1,2-disubstituted benzenes, a y-lactam, and a sugar moiety. The y-lactam contained two quaternary carbons (6 119.5, 132.9). In addition, it had two other quaternary carbons (6 114.6, 115.8). One quaternary carbon (6 123.9) was connected to the sugar moiety through a heteroatom. From NOE experiments of the methylene protons, it was apparent that the methylene is at the C-15 position, confirming the pres-

4.


331

( 2 9 7 ) R = CH3 (298) R = H

ence of a staurosporine-type aglycone. The 2-deoxyfuranoside structure of the sugar moiety was derived from COLOC experiments. Further observations of long-range coupling and NOE experiments showed that C-I' is bonded to N-9 and C-4' to N-14. From these data, the structure of protein kinase inhibitor K-252a was advanced as 297. The 3' configuration and the structure of 297 was confirmed by X-ray crystallographic studies. The structure is identical with the antibiotic SF-2370 (101). Alkaloid K-252b (298, C,,H,,N,O, (M+ 453), mp 262-266°C (dec.), [aID +97" (DMF)} was shown to have similar UV and 1R spectra. The 'HNMR and I3C-NMR data of K-252b were also similar to those of K-252a, except for the absence of the methyl group resonance of the carbomethoxy group. From this evidence it was concluded that K-252a is the methyl ester of K-252b. This was confirmed by hydrolysis of K-252a to give K252b and the methylation of K-252b with diazomethane to yield K-252a. Hence, K252b could be represented by structure 298. 10. UCN-01

UCN-O1(298A), a protein kinase inhibitor, was isolated from Streptomyces sp. (IOla).The IR and UV spectral data of 298A showed it to contain

an indolocarbazole chromophore, like staurosporine, and its 13C-NMR spectrum showed the presence of one amide group, eighteen sp2 carbons, eight aromatic protons, one quaternary carbon, four methines, one methoxy group, one N-methyl group, and one methyl group. From the 'HNMR spectrum the presence of a hydroxyl group at C-14 was detected. Consideration of the 'H-NMR and l3C-NMR data led to structure 298A being assigned to UCN-01 .

J. SYNTHESIS OF HEXACYCLIC BASES In the course of the synthesis of analogs of mahanimbine, Pate1 reported (72) the formation of hexacyclic bases 301 and 302. Photocitral-A (303),

332

D. P. CHAKRABORTY Citral condensation*

R2

OH ( 2 9 9 ) R1 = H 3 R 2 = CH3

obtained by irradiation of citral in sunlight or by reflux in pyridine, reacted with 2-hydroxy-3-methylcarbazole (4) to yield bicyclomahanimbine (304) (13).

H (L1

(303)

1

I

Pyridine reflux

% 3

H

(30L)

K. BISCARBAZOLE ALKALOIDS Biscarbazole alkaloids are enumerated here according to the constituent fragments, beginning with an alkaloid derived from a tricyclic precursor and then progressing to biscarbazoles formed from two tricyclic fragments, one tricyclic and one tetracyclic fragment, two tetracyclic bases, and finally dimers made from tetra- and pentacyclic fragments. 1. Indole Dimer

Kumar et al. (102) isolated from the roots of Murraya gleni an indole dimer [305, C,,H,,N,O, (M+ 414)l. It showed U V (A, 222, 271, 284 nm) and IR (v,,, 3400, 1730 cm-') data for an indole with an ester function. The mass spectral peaks at mlz 231 and 184 showed it to be an indole dimer comprising C,,H,,N02 and C,,H,,N units. The 'H-NMR signals of 305 at 6 7.98 and 6.83 (1H each) showed that one of the indole N H and one H-2 of an indole moiety were substituted. From the 'H-NMR and

4.


333

'H-IH COSY data, the presence of a carbomethoxy group (6 3.33) and two sets of CH2CH,CCH3 groups, one carrying a carbomethoxy group and the other a -NHCHCH cyclized to the indole skeleton of the nonoxygenated fragment, was ascertained. From the coupling of the CHCH group, the stereochemistry of the substituent on the tetrahydrocarbazole was considered to be trans diequatorial. Consequently, structure 305 was derived, which was also substantiated by I3C-NMR and other physical data.

2. Bismurrayafoline-A Bismurrayafoline-A [306, C2,H2,N202 (M+ 4201, mp 176- 177OC1, obtained fromMurraya euchrestfolia (15),had a UV spectrum [A, 228,244, 253 (sh), 284 (sh), 293 nm; log ~4.81,4.95,4.84,4.15,4.80]characteristic of carbazole derivative. The IH-NMR spectrum showed signals for H-5 and H-5' protons (6 7.72, 7.85, d , J = 7 Hz each), H-4 and H-4' protons (6 7.32, 7.36, br s), a complex pattern of eight aromatic protons, an aryl methyl (6 2.46, s), two aromatic methoxy groups (6 3.71 and 3.82), and a benzylic methylene at 6 5.83. The high-intensity peak at mlz 210 (M2+) suggested the isolate to be a dimeric compound. The signal for a twoproton singlet at 6 5.83 and the mass spectral peak at m/z 210 suggested that the benzylic methylene was bonded to the nitrogen atom. On treatment with sodium in liquid ammonia, 306 afforded 307 (mlz 210 and 181), showing the loss of a methoxy group. An N-methyl derivative (307A), obtained on methylation of 307, showed a high-intensity mass spectral

bCH3

(306)

334

D. P. CHAKRABORTY

peak at mlz 224 instead of at mlz 210 and 181, supporting structure 307 for the liquid ammonia reduction product. On hydrogenolysis, 306 afforded murrayafoline-A. Thus, bismurrayafoline-A was formulated as 306.

3. Chrestifoline-D Chrestifoline-D [307B, C,,H,,N,O, (Mi 434)] was isolated as a colorless oil from M. euchrestifolia (21c). From physical data and partial synthesis from bismurrayafoline-A by DDQ oxidation, compound 307B was considered to be the 3-formyl analog of bismurrayafoline-A (307). 4 . Bisrnurrayafoline-B

Bismurrayafoline-B [308, C,,H,,N,O, (M + 588; M2+294)] was obtained from M. euchrestifolia (15). From IR (v,,, 3550, 3150, 1615 cm-') and UV [A, 225 (sh), 265 (sh), 285 (sh), 312, 333 nm, bathochromic shift on addition of alkali] data, it appeared to be a phenolic carbazole. The nineteen carbon signals in the I3C-NMR spectrum, the molecular ion peak at rnlz 588, and the molecular di-ion peak at rnlz 294 showed it to be a dimer comprised of two symmetrical monomer units. The 'H-NMR spectrum of 308 was similar to that of murrayafoline-B except that it lacked the singlet at H-2. From NOE experiments, in which enhancements of the proton signals at H-4 and H-4' were observed on irradiation of the aryl methyl

4.


335

protons, the linkage of the monomers was assigned at the 2,2' position. From these data, structure 308 was assigned to bismurrayafoline-B.

5 . Bismurrayafolinol Bismurrayafolinol [309, C,,H,,N,O, (M 436.1784), colorless oil], obtained from M. euchrestifolia (30), showed UV (A,, 225, 244, 252, 281, 292, 329, 340 nm) and IR spectra suggesting it to be a carbazole alkaloid with a hydroxyl function. From the base peak in the mass spectrum at mlz 210 (Mz+), it was considered to be a dimer. From the 'H-NMR spectrum, the presence of two aromatic methoxy groups, two orthocoupled H-5and H-5'protons (6 7.92 and 8.07, d , J = 8 Hz each), a singlet for H-4 (6 7.74), H-2 and H-2' protons (6 6.78, 7.06), two benzylic methylenes, one attached to the nitrogen (6 6.01) and the other to oxygen (6 4.86), and additional signals for seven protons (6 7.10-7.50) was determined. On comparison of the data with those for bismurrayafoline-A, structure 309 was advanced for bismurrayafolinol, which has been confirmed by the synthesis of its acetate as follows. Murrayanine (2), on reduction with sodium borohydride, gave 3-hydroxymethyl-1-methoxycarbazole, which, on treatment with acetic anhydride, furnished bismurrayafolinol acetate (310). +

(309) R-H ( 3 1 0 ) R-OC.CH3

6 . Oxydimurrayafoline

Oxydimurrayafoline [311, C,,H,,N,03 (M 436.1809)l was obtained as a colorless oil from M. euchrestifolia (30). The UV spectrum (A,, 226, 242, 253, 260, 280, 291, 324, 331 nm) and the base peak at mlz 21 1 in the mass spectrum suggested the presence of a dimeric carbazole skeleton comprising of two murrayafoline A units. 'H-NMR data showed the presence of two NH protons (6 8.27), two aromatic methoxy groups (6 4.01), and two benzylic oxymethylene groups. From NOE experiments, it was found that there was enhancement of the H-2 signal on irradiation of the aromatic methoxy group (6 4.61) and enhancement of the H-4 and H-2 +

336

D. P. CHAKRABORTY

signals on irradiation of the benzylic methylene. Thus, oxydimurrayafoline was formulated as 311.

7. Murrafoline-F Murrafoline F [3U,C2,H,,N202 (M+ 420.181)] was obtained as a colorless oil from M . euchrestifolia (20). It had a characteristic U V spectrum for a carbazole skeleton, and 'H-NMR data showed the presence of two rnethoxy groups (6 4.14, 3.93) and an aromatic methyl (6 2.38). The isolate showed two four-spin proton signals and one three-spin proton resonance, suggesting the presence of two unsubstituted ring A units and a trisubstituted ring C. The signal at 6 4.43 (2H) and a carbon signal at 6 32.2 in the 'H- and 13C-NMR spectra, respectively, could be attributed to a rnethylene group. Enhancement of the H-4 signal on irradiation of a methyl signal and the enhancement of H-4 and H-4' caused by irradiation of the methylene signal showed that H-4, H-4', and H-2' were unsubstituted. 'H-'H COSY data showed the long-range coupling of the proton signal at 6 7.74 with the aryl methyl. Lack of enhancement of any proton signals following irradiation of either methoxy group indicated that one of the rnethoxy groups was at the 1 position and the other was bonded to nitrogen. The location of the second methoxy group bonded to nitrogen was also supported by the intense mass spectral fragment at mlz 390 and the presence of 12 sp2 carbons as doublets in the I3C-NMR spectrum. Thus, murrafoline-F was formulated as structure 312.

4.


337

8 . Murrastifoline-A and -B

Murrastifoline-A [313, C2,H,,N20, (M 420)] and murrastifoline-B [314, C2,H2,N202(M+ 406)], two biscarbazoles comprised of two tricyclic units, were obtained from M . euchrestifolia (103),along with murrastifoline-D and -E, which have tricyclic and tetracyclic units. All of these alkaloids have U V spectra characteristic of a carbazole chromophore. ‘H-’H COSY spectra of the compounds showed that all had common signals for 0methoxy (6 3.57-4.11) and aromatic methyl groups (6 2.52-2.56). Two singlets arising from H-4 (6 7.56-7.63) and another signal for the H-2 proton (6 6.85) were observed in the ’H-NMR spectrum of 313 and 314. The signals for a four-spin proton system indicated the absence of substitution in ring A of one of the constituent carbazole fragments of the bisalkaloids. The position of the methoxy group at C-1 and the methyl group at C-3 of this unit was ascertained from NOE studies. This was further corroborated by the mass spectral fragment at r n l z 210 or 21 1, which could be assigned to the murrayafoline-A structural unit (3), common to all the murrastifoline bisalkaloids. +

’”3-J-y \

In murrastifoline-A, besides the ‘H-NMR signals for the common structural units, signals for a C-methyl (6 2.48), an aromatic methoxy (6 4.13), and H-4 (6 7.54), H-l’, and H-2 protons were observed. It also showed

338

D. P. CHAKRABORTY

signals for H-5 (6 8.10, J = 1.2 Hz), H-6 (6 7.40, dd, J = 1.2, 7.9 Hz), and H-8 protons (6 7.67, d , J = 7.9 Hz). Because H-5 was meta coupled, the linkage of the second unit was at C-6-C-6'. From this evidence, the structure 313 was assigned to murrastifoline-A. In murrastifoline-B (3141, the 'H-NMR data for the second unit showed the presence of an additional four-spin system, demonstrating the absence of substitution in ring A'. The signals for H-4 (6 7.61) and H-2 (6 7.04) were meta coupled (J = 1.5 Hz). Irradiation of the 0-methoxy signal at 6 4.03 showed enhancement of the H-2' signal (6 7.04). Thus, the two units were linked through C-3' of the second unit, and the structure was assigned as 314. 9. Chrestifoline-A

Chrestifoline-A [315, C,,H,,N,O, (M 420)], along with chrestifoline-B and -C (uide infra), was obtained from M. euchrestifolia as an oil (103). It showed a UV spectrum characteristic for a carbazole chromophore. The chrestifolines are built on a common l-methoxy-3-(substituted methy1ene)carbazole unit, as revealed by 'H-NMR spectroscopy. On irradiation of the benzylic methylene, enhancement of the signals of H-4 and H-2 were observed, and the mass spectral fragment at mlz 210 also supports the structure. From the mass spectral data of chrestifoline-A (M+ 420), it was inferred that it had two C,, units. Besides the 'H-NMR signals for the common unit, it had one aromatic methoxy group (6 4.02), an aryl methyl group (6 2.47), an aromatic proton signal at 6 6.94 and a N H proton at 6 10.28. In NOE experiments, irradiation of the aromatic methoxy caused enhancement of the H-2' signal, whereas irradiation of the methyl signal (6 2.07) caused enhancement of the H-2' signal and the benzylic methylene signal. Irradiation of the benzylic methylene signal caused enhancement of the aromatic methyl and the H-5' signal. From these data, structure 315 has been proposed for chrestifoline A. +

4.


339

10. Bismurrayafoline-C and -D Bismurrayafoline-C (316, C,&,N,O,), obtained as a pale yellow oil from M . euchrestifolia (28),showed a UV spectrum characteristic for I oxygenated carbazoles [A, 226,235,260 (sh), 285 (sh), 31 1,335 nm (sh)]. The 'H-NMR signals were similar to those of bismurrayafoline-B (308), but the signal for a dimethylallyl group 308 was replaced by a geranyl chain [6 1.42, 1.47, 1.60 (6Heach) 1.67 (4H, m), 1.75 (4H, m), 3.42 (4H, m), 6.16 (t, 7 . 9 , 4.85 (t, 7.9)] and that for a methoxy by a hydroxyl. The proposed structure was supported by the results of NOE experiments. Irradiation of the aryl methyl signals at 6 2.48 showed enhancement of H-4 and H-4', and irradiation of the benzylic methylene of the side chain showed enhancement of the ally1 methyl (6 1.42) and the N-H. Dimethyl ether derivative 317 showed enhancement of the doublet at 6 6.85 (H-6 and H-6'), confirming the location of the oxygenated substituents at C7 and C-7'. Irradiation of the second methoxy group at 6 3.4 caused enhancement of the N H proton signal at 6 7.85 and the aromatic methyl signal on the other unit, suggesting the location of the second methoxy at C-I. On irradiation of the aromatic methyl at 6 2.52, area increases of the singlets at 6 7.85 (H-4 and H-4') and in the methoxy signal of the other carbazole unit (6 3.4) were observed. These data led to the formulation of bismurrayafoline-C as 316. Bismurrayafoline-D [317, C,,H,,N,O, (M' 724), mp 198-20O"Cl was isolated as a colorless prism (28) along with bismurrayafoline-C. The UV, IR, and 'H-NMR data were very close to those of bismurrayafoline-C. The 'H-NMR spectrum showed the presence of an additional methoxy group (6 3.89). The geranyl side chain was readily discernible from the mass spectral fragmentation at mlz 293 (M*+ - C,H,) and at mlz 239 (M2+ - C,H,). On treatment with diazomethane, the isolate gave an 0tetramethyl ether of bismurrayafoline-C (318). NOE experiments on bismurrayafoline-D (317), after irradiation of the methoxy group (6 3.8),

340

D. P. CHAKRABORTY

indicated an enhancement of the signals of H-6 and H-6', demonstrating the methoxy groups to be at C-7 and C-7' and the hydroxyls at C-1 and C- I '. Thus, bismurrayafoline-D was formulated as 317, the dimethyl ether of bismurrayafoline-C (316). 1 I . Murrafoline-B Murrafoline-B [319, C,,H,,N,O, (M + 474.32), mp 234-237"C], obtained from M. euchrestifolia (104), was considered to be a dimeric carbazole alkaloid from the UV spectrum (A,, 208, 226, 240, 292, 304, 330 nm) and its molecular di-ion peak (M2+ 237). From the 'H-NMR spectrum the presence of one aryl methoxy group (6 3.87), two aryl methyl groups (6 2 4 8 and 2.49), and a dimethyldihydro pyran unit (6 2.30, 2.38,4.69, 1.46, 1.56) was evident. From decoupling experiments, it was inferred that the carbazole had one unsubstituted ring A and another ring A with substitution at C-8. From NOE experiments enhancement of the signals at H-2', H-4', and H-4 were observed on irradiation of the aromatic methyl group, showing that these positions were unsubstituted, whereas irradiation of the methoxy group (6 3.87) led to enhancement of the signal at H-2', indicating the methoxy to be at C-1'. These results, and the mass spectral peaks at m/z 263 and 21 1, indicate that the base is built on a dihydrogirinimbine skeleton and a murrayafoline-A skeleton. Thus, the structure of murrafoline-B was advanced as 319 and confirmed by synthesis, namely, treatment of a mixture of murrayafoline-A and girinimbine with Nafion 117 in refluxing aqueous methanol.

(319 1

(320)

4.


341

12. Murrafoline-D Murrafoline-D (320),isolated from M . euchrestifolia (104, was identified from IR, 'H-NMR, and mass spectral data. It was found to be have TLC behavior identical to a compound obtained during the Nafion 117catalyzed reaction of murrayafoline-A with girinimbine (104). 13. Murrafoline-E

Murrafoline-E [321,C,,H,,N,O, (M+ 420.183 I)]. obtained as a colorless oil (20), showed UV [A,, 228 (sh), 238, 255 (sh), 263 (sh), 287, 320, 340, 352 nm] and IR spectral data for a carbazole derivative. From the mass spectral fragment at mlz 262 and 21 I , it was considered to be a biscarbazole alkaloid with girinimbine and murrayafoline-A units. From the 'H-NMR spectrum, the presence of an aryl methyl (6 2.51). an aryl methoxy (6 3.94), a DMP system [6 1.44 (6H, s), 5.79, 6.92 ( I H , d, J = 10 Hz each)], and a nitrogen-bonded benzylic methylene group (6 6.01) was readily discernible. From 'H-'H COSY experiments, two four-spin systems showing the presence of unsubstituted rings A and A' were ascertained. It appeared from the 'H-'H COSY data and the results of NOE experiments that H-4 and H-2 in the murrayafoline fragment of 321 were unsubstituted. Consequently, the structure of murrafoline-E was assigned as 321. 14. Murrustifoline-D

Murrastifoline-D (322,C,,H,,N,O, (M+ 440.2227), [aID0" (CHCI,)} was obtained from M . euc.'zrestifofiu(103) as a colorless oil. Like its congeners murrastifoline-A and -B, it contained a tricyclic murrayafoline-A unit in which the second tetracyclic unit was bonded through nitrogen. From the mass spectral fragments at mlz 280 (base peak) and at mlz 21 I , the two constituent units were suggested. Oxygen-linked gerninal dimethyl group signals were observed at 6 1.55 and 1.42 along with a double doublet (J = 5.9, 9.2 Hz) at 6 4.38 which was coupled to a hydroxyl proton at 6 4.48 (d, J = 5.9 Hz). The signal at 6 7.2 ( I H , d , J = 9.2 Hz) was as-

dH3 q

\

"

/

(322)

R=OH

(323)

R=H

3

342

D. P. CHAKRABORTY

signed to H-4' as a benzylic carbon directly bonded to the nitrogen of the murrayafoline-A unit. The trans relationship between C-3" and C-4" was ascertained from the coupling constants and the absence of an NOE effect between the methine protons. The 'H-NMR data showed the absence of substitution in rings A and A' of the two units, and the signals at 6 7.87 and 7.56 were attributed to the H-4 and H-4' protons, showing substitution in ring C. From these data, structure 322 was assigned to murrastifoline-D. 15. Murrastifoline-E

Murrastifoline-E (323, C,,H3,,N,02 (M + 474.2280), [aID -5.7" (CHCI,)} was obtained from the same source as its congeners (105). It had a carbazole-like UV spectrum and showed mass spectral fragments at mlz 21 1 and 264 (base peak) arising from the two units. The 'H- and 13C-NMR spectra showed signals for an NH, an aryl methoxy group (6, 4.11, aC 56.89), and two aryl methyl groups (6, 2.56, 2.42, aC 17.56, 22.11). The 'H-NMR data indicated the presence of H-4 and H-4' resonances, and, from proton-proton decoupling experiments, two pairs of four-spin systems were detectable, showing an absence of substitution in rings A and A'. The presence of a dihydropyran (DMPH) ring was detectable from the 'H-NMR and I3C-NMR data. The 'H-NMR signal at 6 7.42 and the appearance of eleven sp2 carbon signals as doublets in the I3C-NMR spectrum showed that the two carbazole units were linked through the benzylic carbon at C-4" and the nitrogen atom of the murrayafoline A unit. From these data, and the results of NOE experiments, structure 323 was assigned to murrastifoline-E, which is evidently deoxygenated murrastifoline-D (322). 16. Chrestifoline-B

Chrestifoline-B [324, C,2H28N202 (M+ 472)] was obtained from M . euchrestifolia (103) as an oil showing a characteristic UV spectrum for carbazoles. The mass spectral fragments at mlz 262 and 248, together with a base peak at mlz 210, suggested the presence of a murrayafolineA unit and a girinimbine unit in the binary system. The presence of a DMP system was readily discernible from the 'H-NMR data [6 1.36 (6H, s), doublets at 6 6.91, 5.53 ( I H , d, J = 9.9 Hz each)]. In a series of NOE experiments, enhancement of the H-4' signal on irradiation of the aryl methyl signal (6 2.27) and enhancements of the signals for H-4" (6 6.91), H-2 (6 6.90), H-8' (6 7.39), and H-4 (6 7.38) were observed on irradiation of the benzylic methylene. These data permitted the formulation of chrestifoline-B as 324.

4.


343

17. Murrastifoline-C Murrastifoline-C (325, C,,H,,H,O, (M+ 540.2773), [aID0" (CHCI,)}, obtained from M . euchrestifolia (103)as a colorless oil, showed, like the other murrastifolines, spectral evidence (UV and IH NMR) for the presence of a 1-methoxy-3-methylcarbazolesystem. Mass spectral fragments at mlz 330 (base peak) and 211 suggested a murrayafoline-A unit and a mahanimbine unit in the binary system. The detection of two sets of four-spin systems in 325 along with results of 'H-'H COSY experiments suggested that rings A and A' were unsubstituted. The 'H-NMR data showed characteristic signals for a DMP system in which one of the methyl groups was extended by an isoprene unit. This inference was also supported from the mass spectrum, in which a fragment at mlz 457 (M+ - 83) was observed. IH-'H COSY exchange and NOESY correlation data showed a broad singlet at 6 7.36 (deshielded H-4') and a signal at 6 6.13 for the benzylic methylene linked to the nitrogen of the murrayafoline-A unit. Thus, murrastifoline-C was formulated as 325.

18. Chrestifoline-C

Chrestifoline-C [326, C,,H,,N,O, (M+ 540)], obtained as a colorless oil from M . euchrestifolia (lo.?),showed a characteristic U V spectrum for carbazoles. Like other chrestifolines, the IH-NMR data and the

344

D. P. C H A K R A B O R T Y

mass spectral fragment at rnlz 210 of chrestifoline-C showed it to contain a l-methoxy-3-(substituted methy1ene)carbazole nucleus. In 'H'H COSY experiments it showed two sets of four aromatic protons, like murrastifoline-C. The 'H-NMR data showed the presence of a DMP system in which one of the methyls was extended by an isoprene unit, like that in mahanimbine. The mass spectral fragment at r n l z 457 (M+ - 83) and the peak at rnlz 248, corresponding to a carbazolopyrillium ion arising from a mahanimbine unit, substantiated the above findings. In NOE experiments, irradiation of the aryl methyl signal (6 2.30) caused enhancement of the H-4' signal, whereas irradiation of the benzylic methylene (6 5.80) caused enhancement of the signals at H - 4 (6 6.95), H-8' (6 7.38), H-4 (6 7.381, and H-2 (6 6.90). From these data the structure 326 has been advanced for chrestifoline-C (103). 19. Murrafoline-C

Murrafoline-C [327, C3,H,,N,0, (M+ 526.261 l)] was obtained as a colorless oil from M . euchrestifolia (104),and the IR and U V data suggested the presence of a carbazole skeleton. The 'H-NMR data showed the presence of four oxygen-linked tertiary methyls (6 1.38, 1.41, 1.42, 1 S2). ABX type signals (6 2.27, 2.31, and 4.63) and AB type signals (6 5.56 and 6.07) represented 2',2'-dimethyldihydropyran and 2',2'-dimethylpyran systems in the molecule. The structure for murrafoline-C has been advanced from comparative assessment of the 'H-NMR data of 327 and rnurrafoline-B, which suggested that a girinimbine unit is linked with a dihydrogirinimbine unit through C-9' and C-8. Consequently, structure 327 is consistent for murrafoline-C and is also supported by the mass spectral fragmentation pattern.

CH3

(327)

20. Murran irn bin e

Murranimbine [328, C3&3&0~ (M' 528.2585)], obtained (106) as a pale racemic oil from M . euchrestifolia, displayed UV and IR data characteristic of a carbazole unit. The characteristic mass spectral fragment at mlz 262.13 showed it to be a bis alkaloid. 'H-NMR data indicated the

4.


345

presence of two aryl methyls (6 2.30, 2.32), four methyls attached to carbons linked with oxygen (6 0.60, 1.54, 1.44, 1.60), and one D,Oexchangeable NH proton (6 10.55). From the ‘H-’H COSY experiments two sets of four-spin aromatic systems were readily detected, which inTwo deshielded signals at 6 7.65 and 8.00 having a cluded H-5 and H-5’. long-range coupling with the aryl methyls were discernible. The results of NOE experiments after irradiation of the aryl methyls confirmed the presence of H-4 and H-4’. ‘H-’H COSY experiments showed the relationship of the signals at 6 6.12 (H-12’, J = 2.9 Hz), 6 2.74 (H-11, J = 2.9, 5.1 Hz), 6 4.07 (H-12), 6 2.21 (H-11, J = 5.16, 12.8 Hz), and 6 2.08 (HI I ) overlapped by a solvent signal. These data, and the results of COSY experiments, showed that the alkaloid contained two girinimbine units in it. Analysis of the homonuclear broad band decoupling (HMBC) spectrum (J = 8 Hz) of murranimbine and the cross-peaks of three-bond correlation related to the connectivity of two units was undertaken. The proton (H12’, 6, 6.12) of the benzylic methylene attached to a nitrogen was related to another benzylic methine ((2-12, 6, 32.4) on the upper unit and to the oxygenated carbon (C-lo’, SC80.3l)in the lower unit, which is also related to the benzylic methine proton (H-12, 6, 4.07) in the upper unit. The methine proton (H-l I ’ , 6,2.74) coupled with both of the benzylic protons (H-12’, 6, 6.12; H-12, 6, 4.07), had a three-bond relationship with an aromatic carbon at C-1 (6, 103.74), and was related to H-11 (6, 2.21) in the upper unit. The methylene carbon at C-11 (6,37.10) was related to the geminal methyl protons at 6,1.44 and 1.60. The three-bond relationships in the HMBC spectrum and other relationships were taken into consideration in assigning the structure of murranimbine. NOE experiments provided information regarding the stereochemistry of the molecule. Enhancements of the signals for H-ll’, H-12, and the N-H signals were observed on irradiation of H-12’. On the other hand, irradiation of H-l 1’ caused enhancements of the signals of H-12’ and H-12. Enhancements of H-l I’ and the methyl signal at 6 1.44 were noticed on irradiation of H-12. Consequently, murranimbine was formulated as 328.

346

D. P. CHAKRABORTY

21. Bis-7-hydroxygirinimbine-Aand -B

7-Hydroxygirinimbine-A [328A, C3&3+04 (M + 556)] and 7hydroxygirinimbine-B (328B,C,,H,,N,04), isolated as pale yellow oils from M . euchrestifolia (106a), had U V spectra very similar to that of girinimbine. The IH-NMR spectrum of 328A showed an aryl methyl singlet, two quaternary methyl singlets, two pairs of AB-type doublets (J = 8.55, 9.6 Hz), and an aromatic proton singlet. The 'H-NMR data, together with ',C-NMR data, suggested the presence of a 7,8-disubstituted girinimbine as the structural unit. Compound 328A gave an 0-methyl derivative on methylation. In differential NOE experiments, enhancement of the H-4 and H-6 signals was observed, indicating methyl and methoxy groups to be at C-3 and C-7, respectively. The linkage of the two girinimbine units was at C-8, C-8'. This was also supported from the HMBC spectrum of the 0-methyl derivative of 328A. The structure of 328B was also determined from U V , IH-NMR, and I3C-NMR data. The compound gave an 0-methyl derivative on methylation, and NOE experiments on the derivative indicated the linkage of the

HO

4.


347

two girinimbine units to be at C-8 and C-6'. The possibility of the coupling of the two monomers during isolation has not been ruled out. 22. Murrafoline Murrafoline (329, C,,H,,N,O, (M+ 594), [aID0" (CHCI,)}, the first bis alkaloid to be reported, was isolated from the root bark of Murraya euchrestifolia (107). The IR and UV data for 329 [A,,, 218, 243, 260 (sh), 307, 332 nm, with log E 4.66,4.80,4.66,4.45, 3.911 revealed it to be a carbazole derivative. The 'H-NMR spectrum showed the presence of two aryl methyl groups (6 2.28, 2.37), a vinyl methyl (6 1.54), three tertiary methyls on a carbon linked to oxygen, a triplet arising from a benzylic group (6 4.58), a multiplet (6 3.24), and overlapping unresolved signals for thirteen protons in the aromatic region [S 6.70-7.90, two of which disappeared on deuteration (NH)]. The molecular di-ion peak at rnlz 297 and the ion peak at rnl z 594 showed it to be a bis alkaloid. The complete structure and relative stereochemistry were obtained from single-crystal X-ray analysis as 329.

L.

S Y N T H E S I S OF

BISCARBAZOLES

Biscarbazole formation in connection with studies of carbazole alkaloids is discussed here. Various other methods of dimerization, including electrochemical methods, have been reviewed by Joule ( 1 0 7 ~ ) . Under Udenfriend reaction conditions, 3-methylcarbazole (6) furnished a dimeric compound (330) in poor yield, along with other hydroxycarbazoles (55). A methanolic solution of murrafoline-A and girinimbine, when

348

D. P. CHAKRABORTY

refluxed in methanol in presence of Nafion 117, yielded a mixture of biscarbazoles, namely, murrafoline D and two other alkaloids (331 and 332) (104). When girinimbine and derivatives 333 and 334 were treated for a short time with boron trifluoride etherate, dimeric carbazoles were obtained (337-339). The reaction has been mechanistically represented as shown (108).

4.

CHEMISTRY A N D BIOLOGY O F CARBAZOLE ALKALOIDS

349

IV. Physical Properties of Carbazole Alkaloids Applications of physical methods for the structural determination of carbazole alkaloids have been previously reviewed (6,13). Here we report some of the salient features and new findings. A. ULTRAVIOLETABSORPTION SPECTRA Extensive application of ultraviolet absorption spectroscopy to carbazole alkaloids has been made in detecting the carbazole and indolocarbazole chromophores in the respective alkaloids. The positions of the formyl, methoxy, and methyl groups continue to be deduced from UV data (16,13,33) and are confirmed subsequently by other data or by synthesis. UV absorption data for a large number of alkaloids have been detailed in previous reviews (6, 13).

B. INFRARED SPECTRA The characteristic IR bands for carbazoles and methylsubstituted carbazoles as reported by Richards (109) were utilized by Chakraborty in the structural determination of degradation products (6). Recently, the IR bands near 750 cm-' have been found to be characteristic for the unsubstituted ring A of carbazomycins. The IR bands at low frequency (1630-1645 cm-I) have been considered characteristic for a formyl group at C-3 chelated to the hydroxyl at C-2 in several alkaloids (13). C. NMR SPECTRA 1. ' H - N M R Spectra The presence of a carbazole skeleton in the first carbazole alkaloid murrayanine was detected by 'H-NMR spectroscopy (6). Discussions on 'H-NMR spectra of the alkaloids have been presented with data for various compounds in previous reviews (6,13). The low-field H-5 and H-4 signals (6 7.17-7.50) and their shift caused by neighboring protons have been extensively utilized for the detection of substitution in rings A or C. The presence of an isolated four-spin system (6 7.06-7.90) has been considered indicative of the presence of an unsubstituted ring A. The characteristic signals for a 3,3-dimethylallyl (DMA) side chain have been utilized in their detection. The olefinic doublets at around 6 6.2 and 5.4 (J = 10 Hz each) and the signal for a gem-dimethyl group have been utilized for the detection

350

D. P. CHAKRABORTY

a 2,2-dimethyl-A3-pyran (DMP) system fused to the carbazole skeleton. In compounds of the mahanimbine type, where one of the methyl signals has been extended by a DMA unit, consequent changes in the spectrum have been observed. NOE experiments have been extensively used for confirming the assignments of proton signals. In the case of some complex compounds the more informative INEPT method has been utilized. 2. 13C-NMR Spectra Diagnostic chemical shifts for C-1 to C-8 were first utilized in the case of carbazomycins-A and -B (10,13). A short discussion on the shift of the carbon signals as compared with those of benzene signals has been presented by Chakraborty and Roy (13). Carbon-1 in 2-oxygenated carbazoles experiences shift effects owing to both oxygen and nitrogen atoms (13). Similar shifts of C-8 have also been found in the case of 7-oxygenated compounds (25). Thus, in the case of several 2- and 7-oxygenated compounds (e.g., 38 and 39) both C-1 and C-8 signals appear at around 6 96.0. Modern two-dimensional NMR techniques like COSY, HETCOR, COLOC, and other techniques have been utilized for the confirmation of structures of complex alkaloids. The structural determination of Tan1030A and Tan-999 are interesting in this respect (98). I3C-NMR data of several carbazole alkaloids have appeared in previous reviews (10,13). D. MASS SPECTRA Mass spectral investigations have been extensively utilized for the structure determination of carbazole aklaloids. Various modern mass spectral methods have been employed in arriving at a correct mass for a molecule. Apart from this, mass spectrometry studies have provided interesting information on various structural aspects. For example, the carbazolopyrillium ion found in mass spectra of pyranocarbazoles like girinimbine and mahanimbine has given adequate information for the presence of this tetracyclic system. When the pyran ring is hydrogenated, a different characteristic spectrum is obtained. Molecular di-ion peaks have also been utilized for detecting some bisalkaloids. Brief discussions on this subject have appeared in previous reviews (6,13). E. X-RAYCRYSTALLOGRAPHY X-Ray crystallographic methods have been utilized in the structural determination of various alkaloids, the first being that of murrayazoline. The structures of murrafoline (329) and staurosporine (251) have primarily been elucidated by X-ray crystallographic methods, whereas for

4.


351

carbazomycin-B (1271, -C (105), -G (1101, chlorohyellazole (90), K-252a (2971, and kinamycin-C (209) X-ray methods have confirmed the structures deduced by other methods.

V. Biogenesis of Carbazole Alkaloids Previous reviews have discussed the biogenesis of 3-methylcarbazole, the origin of the functional variants of aromatic methyl group in carbazole alkaloids, the hydroxylation pattern of the compounds, and the biosynthesis of carbazomycins and kinamycins (5,6,10,13). 3-Methylcarbazole (6) has been considered by Kapil ( 5 ) to be the key precursor compound in higher plants. Chakraborty (12) suggested that 2-methylcarbazole (153) could be the key compound in the pathway operating in fungi and bacteria and also suggested that both 3- and 2-methylcarbazoles arise from 2- and 3-prenylated indoles. Since the report on the structure of echinulin in 1943 (110), there had been wider interest in studies on the prenylation of indoles (111,112). The primary electrophilic attack of the prenyl chain occurs at the 3 position of the indole skeleton, which may subsequently migrate to other positions. Kapil (3,as well as Erdtman (112a), conceived that 3-prenylated indole gives rise to 3-methylcarbazole via prenylated 2-indole after rearrangement. Isolation from Murraya gfeni of the dimeric indole 305 by Kumar et a f . (102), which contains a 2-methyltetrahydrocarbazole with another unit of 3-prenylated indole containing a carbomethoxy group, provides the first circumstantial evidence for the formation of 2-methylcarbazole from a 3prenylated indole, although paniculidin-A (340) was isolated from Murraya panicufata in 1985 (113). Thus, evidence supporting the formation of 2methylcarbazole from prenylated indole is strengthened. The occurrence of tubingensin-A, -B, and aflavazole in members of the genus Aspergillus containing polyprenylated indoles also contributes to the idea that 3- or 2-methylcarbazole or their terpenoid analogs arise from prenylated or polyprenylated indoles.

H (340)

352

D.

P.

CHAKRABORTY

Biosynthetic experiments (1 14) on carbazomycin-B have shown that C2 and C-1 with their methyl substituents arise from a pyruvate unit via acetyl-coenzyme A. Thus, in the biosynthesis of carbazomycins both the tryptophan and pyruvate pathways participate. Insight into the formation of indolocarbazoles has been derived from studies on the biosynthesis of staurosporine (251) and rebeccamycin (254). Biosynthetic studies of rebeccamycin (86) have shown that rebeccamycin arises from two molecules of tryptophan, one of glucose (341), and one of methionine (342). Evidence has also been provided that the a-amino group of tryptophan does not contribute to the phthalimide fragment, suggesting that no symmetrical indole intermediate is involved in the biosynthesis of the alkaloid. Studies on the biosynthesis of staurosporine by Meksuriyen and Cordell (89) have shown that the aglycone moiety (343) of staurosporine is derived from two units of tryptophan with the carbon skeleton intact. Further experimental results are necessary to establish the nature of the intermediate in the biotransformation of tryptophan to staurosporine.

VI. Biochemical and Medicinal Properties of Carbazole Alkaloids and Related Compounds Earlier in this treatise, Kapil(5) mentioned some of the biological properties of carbazole alkaloids. Since then, wider interest in this area has developed (6,8,10,13). Some important properties and some new reports are summarized below. A. ANTIMICROBIAL PROPERTIES Antimicrobial properties of carbazole alkaloids received attention beginning with the report of the activity of murrayanine (2) and other alkaloids of M. koenigii (4). The antibiotic properties of carbazomycin-B (127) and

4.


353

related compounds attracted wider attention. Carbazomycin-B was active against the fungi Glomerella cingulata N 13 and Elsinoe fawcettii at a minimum inhibitory concentration (MIC) of 3 pg/ml, whereas against Trychophyton asteroides 429 and Trychophyton mentagrophytes 833 it was active at a concentration of 12.5 pg/ml. Demethylated glycozoline (197) was active against Trychophyton sp. at aconcentration of 10 pglml. Phenolic compounds were more active than their O-methyl derivatives (13). Tetracyclic kinamycins have been found to be active against a large number of bacteria and fungi. The activities of the kinamycins have been found to decrease with the larger number of acetoxy groups. Thus, the relative order of antimicrobial properties are kinamycin-B, -D, -A, and -C (217,218, 216, 209). The MIC values of kinamycin-B are 0.012 pg/ml against Bacillus subtilis PCI-219, Staphylococcus aureus, Bacillus anthracis, and Staphylococcus albus, and 0.9 to 0.19 pg/ml against Vihrio coma. Deacetylkinamycin-D derivatives show substantial activity against Mycobacterium ATCC 607 and gram-negative Escherichia coli NIHJ, Klebsiella pneumoniae, and Shigella sonnei (65b). The antimicrobial properties of the indolocarbazoles have received widespread attention. The activity of staurosporine (251)against various bacteria and fungi has been examined (83). It has been reported to be active against Candida albicans, Cundida pseudotropicalis, Saccharomyces sake, Aspergillus brevipes, Trichophyton rubum,Sclerotinia cinerea, and Piricularia oryzae at MIC values of 6.25, 3.13, 3.13, 3.13, 6.25, 0.78, and 0.78 pg/ml, respectively. Alkaloids AT 2433-Al, -A2, -B1, and -B2 were found to be active against gram-positive Micrococcus luteus, Bacillus subtilis, Staphylococcus aureus, Streptococcus jaecalis, and Streptococcus faecium. AT 2433-B 1 was also active against the gramnegative bacterium Escherichia coli SS 1431 (91,100).Alkaloid SF 2370

(216 (217)

R1 = R2= R 3 = COCH3; R b = H R ~ = R J = R L = H ; R ~ = COCH3

2 1 8 R 1 = R3 = C O C H3 ;R2 = RL = H ( 2 0 9 ) R ~ = R ~ = R L = C O C H ~R;2 = H (

354

D. P. CHAKRABORTY

(identical with K-252a) has been examined with several microbes and was found to be active against Micrococcus luteus, Micrococcus frcluus FDA 16, and Corynebacteriurn bouis 1810 at a concentration of 6.25 pg/ml (202). B. ANTITUMOR A N D TUMOR-PROMOTING ACTIVITY Kinamycin C (209) has weak antitumor activity against Ehrlich ascites carcinoma and sarcoma 180 (66). In the brine shrimp assay, 7methoxymukonal (40) was more active than 7-methoxyheptaphylline (@A), whereas against the NT-29 cell lines, 7-methoxyheptaphylline was more active than 7-methoxymukonal (25). Antibiotics AT 2433-A 1 and AT 2433-B 1 (272,274) were found to be effective in prolonging the lifespans of mice transplanted with the leukemia P338 tumor (92,200).Rebeccamycin (254) has been found to have antitumor activity (86a). Growth inhibition of mammary carcinoma by compound 344 has been observed at 1 Fg/ml (225). Staurosporine is cytotoxic against NB- 1 cells; it induces elongation . also shows in uitro of neurites and cell enlargement ( 2 2 5 ~ )Staurosporine antineoplastic activities against cancer cells (2256)and a strong cytotoxic M effect on the growth of HeLa S3 cells, with an IC,, value of 4 x (I I5c).

mcoo c2 H 5

I

I

N-Methylcarbazole (345) is a carcinogen and mutagenic constituent of tobacco smoke. This alkaloid is converted by primary cultures of rat heptatocytes to N-hydroxymethylcarbazole (346)and carbazole (1).The cytotoxicity of N-hydroxymethylcarbazole was greater than that of the

4. CHEMISTRY A N D BIOLOGY OF CARBAZOLE ALKALOIDS

355

parent N-methylcarbazole. Hydroxylation of N-methylcarbazole is considered a toxicant step, whereas its dealkylation to carbazole is likely to be a detoxification step (116). 3-Hydroxymethyl-I-methoxycarbazole (koenoline-27) has been shown to be a cytotoxic agent (19). l,lO-Bis(6methyl-5H-benzo[b]carbazol-1 I-y1)decane (346A) has a potential bifunctional DNA intercalating property (117). C. ANTIVIRAL ACTIVITY Several carbazoles have been examined for antiviral activity. In uitro activity against herpes simplex virus type- 1 by tubingensin-A (246) and tubingensin-B (247) were reported. Carprofen (347) increased interferon (IFN) produced by 10-carboxymethyl-9-acridenone (CMA, suboptimal concentration) in murine cell cultures. The CMA-induced IFN production was increased 500-fold in pure bone marrow-derived macrophage cultures. The activity has been shown to be related to cyclooxygenase (118). Some bis-basic ethers of carbazoles are antiviral. When tested against Encephalomyocardis virus infection, several 9-ethyl-substituted bis-basic carbazoles with the general formula 348 have been shown to be active (13).

“‘m /COOH

\

N

“CH3

H

(347 1

R

2

m

R

t.’

R (348) R=H,Me,Et R1 = COOR, C O N M e 2

3 R2 = Et

N H S 0 , G

H

(349)

’

/ Bu / h e x y l

OH

(2L5A)

D. CARDIOVASCULAR-MODULATING ACTIVITY Murrayaquinone A (69) has been found to produce a triphasic inotropic response (119). This triphasic pattern of inotropism was unaffected by reserpine, metoprolol, or cimetidine treatment and is not mediated through a receptor mechanism but, rather, through a mechanism involving ATP

356

D. P. CHAKRABORTY

production. In rabbits, the sudden death produced by arachidonic acid was antagonized by pretreatment with Bay U 3405 (349), showing it to be a thromboxane A2 antagonist with antithrombolic activity. Murrayazolinine (245A) caused sudden lowering of blood pressure in experimental subjects. The action of (245A) is probably not mediated through muscarine H, or H, receptors (120). Staurosporine has been found to have hypotensive activity (83). K-252b and K252c seriously affect the functions of platelets, mast cells, and several other cells and tissues (91).

E. CENTRAL NERVOUS SYSTEM ACTIVITY Behavioral changes in animals have been recorded following administration of some tetrahydrocarbazoles having alkylamino substitution in the aromatic ring (121). Compounds 350 and 352 induce an abnormal behavioral pattern, whereas 351 does not. Some tetrahydrocarbazoles of general formula 353 induce inhibition of gastric secretion (13).

(350) R = C H 2 P h (351) R = H

(352)

(353) R = Me/ E t / C H M q / C H 2 C M e 3 / C M e

R1 = N M e 2 / N E t 2 / p y r i m i d y n y I / 1-piper I d y n y l

Some carbazole derivatives are useful in the treatment of psychotic disorders, anxiety, pain, and gastrointestinal dysfunction (122). Some neuroleptic agents like cycloindole (354) and flucindole (355) have found use in therapy; whereas cycloindole has antidepressant activity, flucindole shows antipsychotic activity (123). Tetrahydrocarbazoles of the general formula 356 are useful central nervous system agents. They have also antiparkinson activity (124).

4.


R

R

357

=H

(35L

Cycloindole

(355

Flucindole R = F

-f3zo-zN3R1 \

N

/

H

(356) R = Alkyl, Alkoxy, Alkylthio, S u l f o n y l s u l f one , O H , F , C I , B r , C F 3 , Cyano, Methylene dioxy Z = CH2 /H2-CH2

R1= Ph

Rincazole (357),a novel neuroleptic and antipyretic agent (125,126),has evoked a great interest. The effects induced by phencyclidine, a 6-opioid antagonist, are counteracted by 357. It indirectly affects dopamine neurons, displaying selectivity for A 10 dopamine cells. It increases the concentration of neurotensin in the caudate nucleus. A constituent of bovine urine, 3-chlorocarbazole (UO),has been shown to have diazepam-like activity (48).

F. ANTI-INFLAMMATORY PROPERTIES Anti-inflammatory properties of several carbazole derivatives have attracted widespread attention. 6-Chloro- I ,2,3,4-tetrahydrocarbazolehas been found to be useful against treatment of gout (10). I-Ethyl-8-N-propyl1,2,3,4-tetrahydrocarbazole1-acetic acid (358) is an anti-inflammatory

358

D.

P. CHAKRABORTY

agent (10). Other complex tetrahydrocarbazoles of general structure 359 and 360 have also been found to have anti-inflammatory properties (13). Carprofen (347) has received significant attention as a substitute for nonsteroidal and nonalkaloidal anti-inflammatory substances. Its activity is comparable to indomethacin, with less toxic side effects (production of gastric ulcer and blockade diarrhea) (127). In uitro cellular effects of carprofen were found to be greater than those of ibuprofen and almost comparable to those of hydrocortisone (128).The anti-inflammatory activity of carprofen is probably dependent on inhibition of some neutrophil macrophage function. It stimulates acid secretion without affecting basal acid secretion (129). This enhancement of secretagogue-stimulated acid secretion was dependent extracellular calcium. It has been suggested that the compound acts at postreceptor site between adenylate cyclase and a protein pump. The drug probably increases calcium efflux through the plasma membrane and decreases the endogenous prostaglandin E, content.

G. MODULATION OF ENZYME ACTIVITY, METABOLISM, AND ALLERGIC REACTIONS 3-Chlorocarbazole (120) is a potent inhibitor of rat liver monoamine oxidase (13). The inhibition of lipid peroxidation induced by free radicals generated in the presence of Fe2+and ascorbic acid by carazostatin (112)

4.


359

is higher than that with the brain protective agent lunarizine, which has afree radical-scavenging activity. As an antioxidant, it is better than butylated hydroxytoluene. Carazostatin may be helpful for alleviation of tissue damage due to the action of superoxide radicals and subsequent peroxidative disintegration of cell membranes (46).Carbazomycin-B and -C (127, 105) were found to inhibit lipooxygenase activity, which could be related to free radical-scavenging effects (130). Alkaloids K-252a, -b, -c, -d (91), and UCN-01 ( 1 0 1 ~have ) been found to be inhibitors of protein kinase C. The indolocarbazole aglycone moiety has been considered to be required for such inhibitory activity. The protein kinase C inhibitory activity of Tan-999, Tan- 1030A, and staurosporine also support this contention. Unlike K-252a, K-252b appeared to lose the calmodulin selectivity; not only Ca2+/calmodulin-dependent activity but also the basal activity of Ca2+/calmodulin-dependent phosphodiesterase were affected (91). Macrophage-activating activity is associated with the antitumor and antimicrobial activity through augmentation of phagocytic activity. Tan-999, Tan-l030A, and staurosporine were found to be macrophageactivating substances. They augment phagocytic activity of murine macrophage cells. The activity of p-glucouronidase, a lysosomal enzyme, is a marker for macrophages related to bacterial infection. Tan-999 increased the activity of this enzyme at 5 pg/ml. Tan-1030A had substantial activity, but staurosporine had little activity on this enzyme. The phagocytosisdependent respiratory burst in mouse peritoneal macrophages was found to increase with Tan-999 (0.01-1 pg/ml) and Tan-1030A (1-10 pg/ml). It has been suggested that the specific inhibitors of protein kinase-C are expected to act as macrophage activators that could provide protection against tumor development and microbial infection through phagocytic activity (83,98,99). Oxarbazole (361) shows antiallergic activity (123).

H. MISCELLANEOUS EFFECTS Trypanocidal effects have been shown by substituted 1,2,3-tetrahydro carbazoles (131). Some carbazole derivatives have larvacidal and insecticidal activity (132). Inhibitory effects (80,81) on the crop pest Heliofhis zea

360

D. P. CHAKRABORTY

have been shown by tubingensin-A and -B. Carbazole-N-carboxamide (362)has been found to have growth inhibitory activity (133). SF-2370 has been found to have effects against rice plant diseases and the greenhouse blights caused by Rhizocotonia solani, Xanthomonas campestris pv oryzae, and Piricularia oryzae (101).

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CUMULATIVE INDEX OF TITLES

Aconitum alkaloids, 4, 275 (19S4), 7,473 (1960), 34,95 (1988) C I 9diterpenes, 12, 2 (1970) Cz0 diterpenes, 12, 136 (1970) Acridine alkaloids, 2, 353 (1952) Acridone alkaloids, experimental antitumor activity of acronycine, 21, 1 ( 1983) N-Acyliminium ions as intermediates in alkaloid synthesis, 32, 27 1 ( 1988) Ajmaline-Sarpagine aklaloids, 8,789 (1965), 11,41 (1968) Alkaloid production, plant biotechnology of 40, 1 (1991) Alkaloid structures spectral methods, study, 24, 287 (1985) unknown structure, 5, 301 (1955), 7,509 (1960), 10,545 (1967), 12, 4.55 (1970), 13,397 (1971), 14, 507 (1973), 15,263 (1975), 16, 511 ( 1977) X-ray diffraction, 22, 5 1 (1983) Alkaloids forensic chemistry of, 32, 1 (1988) histochemistry of, 39, I (1990) in the plant, 1, 15 (1950), 6, 1 (1960) Alkaloids from Amphibians, 21, 139 (1983), 43, 185 (1993) Ants and insects, 31, 193 (1987) Chinese Traditional Medicinal Plants, 32, 241 (1988) Mammals, 21, 329 (1983),43, I19 (1993) Marine organisms, 24,25 (1989, 41,41 (1992) Mushrooms, 40, 189 (1991) Plants of Thailand, 41, 1 (1992) Allelochemical properties o r the raison d'Ctre of alkaloids, 43, 1 (1993) A110 congeners, and tropolonic Colchicum alkaloids, 41, 125 (1992) Alstonia alkaloids, 8, 159 (1965), 12,207 (1970),14, 157 (1973) Amaryllidaceae alkaloids, 2,33 1 (1952), 6, 289 (1 9601, 11, 307 ( 1968), 15,83 (1975), 30, 251 (1987) Amphibian alkaloids, 21, 139 (1983). 43, 185 (1983) Analgesic alkaloids, 5, 1 ( 1 9 s ) 36s

366


Anesthetics, local, 5, 21 1 (1955) Anthranilic acid derived alkaloids, 17, 105 (1979), 32, 341 (1988), 39, 63 ( 1990) Antifungal alkaloids, 42, 117 (1992) Antimalarial alkaloids, 5, 141 (1955) Antitumor alkaloids, 25, 1 (1985) Apocynaceae alkaloids, steroids, 9, 305 (1967) Aporphine alkaloids, 4, 119 (1954), 9, I (1967), 24, 153 (1985) Arisrolochia alkaloids, 31, 29 (1987) Arisrotelia alkaloids, 24, 113 (1985) Aspergillus alkaloids, 29, 185 (1986) Aspidosperma alkaloids, 8, 336 (1965), 11, 205 (1968), 17, 199 (1979) Azafluoranthene alkaloids, 23, 301 (1984) Bases simple, 3, 313 (1953),8, 1 (1965) simple indole, 10, 491 (1967) simple isoquinoline, 4, 7 (1954), 21, 255 (1983) Benzodiazepine alkaloids, 39, 63 (1990) Benzophenanthridine alkaloids, 26, 185 (1985) Benzylisoquinoline alkaloids, 4, 29 (I954), 10,402 (1967) Betalains, 39, I (1990) Biosynthesis, isoquinoline alkaloids, 4, I (1954) Bisbenzylisoquinoline alkaloids, 4, 199 (1954), 7,429 (19601, 9, 133 (1967), 13, 303 (1971), 16, 249 (1977), 30, 1 (1987) synthesis, 16, 319 (1977) Bisindole alkaloids, 20, 1 (1981) Bisindole alkaloids of Catharanthus, C-20’ position as a functional hot spot in, 37, 133 (1990) isolation, structure elucidation and biosynthesis, 37, 1 (1990) medicinal chemistry of, 37, 145 (1990) pharmacology of, 37,205 (1990) synthesis of, 37,77 (1990) therapeutic use of, 37,229 (1990) Buxus alkaloids, steroids, 9, 305 (l967), 14, 1 (1973), 32,79 (1988) Cactus alkaloids, 4, 23 (1954) Calabar bean alkaloids, 8, 27 (1965),10,383 (1967), 13,213 (1971), 36, 225 (1989) Calabash curare alkaloids, 8,515 (1965), 11, 189 (1968) Calycanthaceae alkaloids, 8,581 (1965) Camptothecine, 21, 101 (1983) Cancentrine alkaloids, 14,407 (1973)


367

Cannabis satiua alkaloids, 34, 77 (1989) Canthin-6-one alkaloids, 36, 135 (1989) Capsicum alkaloids, 23, 227 (1984) Carbazole alkaloids, 13,273 (1971), 26, 1 (1985) chemistry and biology of, 44,257 (1993) Carboline alkaloids, 8,47 (1969, 26, I (1985) P-Carboline congeners and Ipecac alkaloids, 22, 1 (1983) Cardioactive alkaloids, 5,79 (1955) Celastraceae alkaloids, 16, 2 15 (1977) Cephalotaxus alkaloids, 23, 157 (1984) Cevane group of Veratrum alkaloids, 41, 177 (1992) Chemotaxonorny of Papaveraceae and Fumaridaceae, 29, 1 (1986) Chinese medicinal plants, alkaloids from, 32, 241 (1988) Chromone alkaloids, 31, 67 (1987) Cinchona alkaloids, 3, 1 (1953), 14, 181 (1973), 34, 332 (1989) Colchicine, 2, 261 (1952), 6, 247 (1960), 11,407 (1968), 23, 1 (1984) Colchicum alkaloids and allo congeners, 41, 125 (1992) Configuration and conformation, elucidation by X-ray diffraction, 22, 5 1 (1983) Corynantheine, yohimbine, and related alkaloids, 27, 131 (1986) Cularine alkaloids, 4, 249 (1954), 10, 463 (1967),29, 287 (1986) Curare-like effects, 5, 259 (1955) Cyclic Tautomers of Tryptamine and Tryptophan, 34, 1 (1989) Cyclopeptide alkaloids, 15, 165 (1975) Daphniphyllum alkaloids, 15,41 (1975),29, 265 (1986) Delphinium alkaloids, 4,275 (1954), 7,473 (1960) Clo-diterpenes, 12,2 (1970) Czo-diterpenes, 12, 136 (1970) Dibenzazonine alkaloids, 35, 177 (1989) Dibenzopyrrocoline alkaloids, 31, 101 ( 1987) Diplorrhyncus alkaloids, 8, 336 (1965) Diterpenoid alkaloids Aconitum, 7,473 (1960), l 2 , 2 (1970), 12, 136 (1970),34,95 (1989) Delphinium, 7,473 (1960), 12, 2 (1970), 12, 136 (1970) Garrya, 7,473 (1960), 12,2 (1960), 12, 136 (1970) chemistry, 18,99 (1981), 42, 151 (1992) general introduction, 12,xv (1970) structure, 17, 1 (1970) synthesis, 17, 1 (1979) Eburnamine-vincamine alkaloids, 8, 250 (1965), 11, 125 (1968), 20, 297 (1981), 42, l(1992)

368


Efaeocarpus alkaloids, 6, 325 (1960) Ellipticine and related alkaloids, 39, 239 (1990) Enamide cyclizations in alkaloid synthesis, 22, 189 (1983) Enzymatic transformation of alkaloids, microbial and in uito, 18, 323 (1981) Ephedra alkaloids, 3, 339 (1953) Ergot alkaloids, 8,726 (1965),15, 1 (I975),39,329 (1990) Erythrina alkaloids, 2,499 (1952), 7, 201 (1960), 9,483 (1967), 18, 1 (1981) Erythrophfeurn alkaloids, 4, 265 (1954), 10, 287 (1967) Eupomutia alkaloids, 24, I (1985)

Forensic chemistry, alkaloids, 12, 5 I4 (1970) by chromatographic methods, 32, 1 (1988) Gafbulirnirna alkaloids, 9, 529 (1967), 13, 227 (1971) Gardneria alkaloids, 36, 1 (1989) Garrya alkaloids, 7,473 (l960), 12, 2 (1970), 12, 136 (1970) Geissosperrnum alkaloids, 8, 679 (1965) Gelsemiurn alkaloids, 8,93 (1963, 33, 84 (1988) Glycosides, monoterpene alkaloids, 17,545 (1979) Guatteria alkaloids, 35, 1 (1989) Haplophyton cimicidurn alkaloids, 8, 673 (1965) Hasubanan alkaloids, 16,393 (1977), 33, 307 (1988) Histochemistry of alkaloids, 39, 165 (1990) Hofarrhenagroup, steroid alkaloids, 7, 3 19 (1960) Hunteria alkaloids, 8, 250 (1965) lhoga alkaloids, 8,203 (1965),11,79 (1968) Imidazole alkaloids, 3, 201 (1953), 22, 281 (1983) Indole alkaloids, 2, 369 (1952), 7, 1 (1960), 26, I (1985) distribution in plants, 11, I (1968) simple, 10, 491 (1967), 26, 1 (1985) Reissert synthesis of, 31, 1 (1987) Indolizidine alkaloids, 28, 183 (1986). 44, 189 (1993) 2,2'-Indolylquinuclidine alkaloids, chemistry, 8, 238 (196% 11, 73 ( 1968) Ipecac alkaloids, 3, 363 (1953), 7,419 (1960), 13, 189 (1971), 22, 1 (1983) Isolation of alkaloids, 1, I (1950) Isoquinoline alkaloids, 7, 423 (1960) biosynthesis, 4, 1 (1954) "C-NMR spectra, 18,217 (1981) simple isoquinoline alkaloids, 4 , 7 (1954), 21, 255 (1983) Reissert synthesis of, 31, 1 (1987)


369

Isoquinolinequinones, from Actinomycetes and sponges, 21, 55 (1983) Khat (Catha edulis) alkaloids, 39, 139 (1990) Kopsia alkaloids, 8, 336 (1965) Lead tetraacetate oxidation in alkaloid synthesis, 36, 70 (1989) Local anesthetics, 5, 21 I (1955) Localization in the plant, 1, 15 (1950), 6, 1 (1960) Lupine alkaloids, 3, 119 (1953), 7, 253 (1960), 9, 175 (1967), 31, 16 ( 1987) Lycopodium alkaloids, 5,265 (1955),7,505 (1960), 10, 306 (l967), 14, 347 (1973), 26,241 (1985) Lythraceae alkaloids, 18, 263 (1981), 35, 155 (1989) Mammalian alkaloids, 21, 329 (l983), 43, 119 (1993) Marine alkaloids, 24, 25 (1983, 41,41 (1992) Maytansinoids, 23,71 (1984) Melanins, 36, 254 (1989) Melodinus alkaloids, 11, 205 (1968) Mesembrine alkaloids, 9,467 (1967) Metabolic transformation of alkaloids, 27, 323 (1986) Microbial and in uifro enzymatic transformation of alkaloids, 18, 323 (1981) Mifrugyna alkaloids, 8, 59 (1965), 10, 521 (1967), 14, 123 (1973) Monoterpene alkaloids, 16, 431 (1977) glycosides, 17, 545 (1979) Morphine alkaloids, 2, 1 (part 1, 1952), 2, 161 (part 2, 1952), 6, 219 (1960), 13, 1 (1971) Muscarine alkaloids, 23, 327 (1984) Mushrooms, alkaloids from, 40, 190 (1991) Mydriatic alkaloids, 5, 243 (1955) a-Naphthophenanthridine alkaloids, 4, 253 (1954), 10,485 (1967) Naphthylisoquinoline alkaloids, 29, 141 (1986) Narcotics, 5 , 1 (1955) Nuphar alkaloids, 9,441 (1967), 16, 181 (1977), 35,215 (1989) Ochrosia alkaloids, 8, 336 (1963, 11, 205 (1968) Ourouparia alkaloids, 8, 59 (1965), 10, 521 (1967) Oxazole alkaloids, 35, 259 (1989) Oxaporphine alkaloids, 14, 225 (1973) Oxindole alkaloids, 14, 83 (1973)

Papaveraceae alkaloids, 19,467 (1967), 12, 333 (l970), 17,385 (1979) pharmacology, 15,207 (1975) toxicology, 15,207 (1975)

370


Pauridiantha alkaloids, 30, 223 (1987) Pavine and isopavine alkaloids, 31, 3 17 (1987) Pentaceras alkaloids, 8,250 (1965) Peptide alkaloids, 26, 299 (1985) Phenanthrene alkaloids, 39,99 (1990) Phenanthroindolizidine alkaloids, 19, 193 (1981) Phenanthroquinolizidine alkaloids, 19, 193 (1981) P-Phenethylamines, 3, 313 (1953), 35,77 (1989) Phenethylisoquinoline alkaloids, 14, 265 (19731, 36, 172 (1989) Phthalideisoquinoline alkaloids, 4, 167 (1954), 7, 433 (19601, 9, 117 (1967), 24, 253 (1985) Picralima alkaloids, 8, 119 (1965), 10, 501 (19671, 14, 157 (1973) Piperidine alkaloids, 26,89 (1985) Plant biotechnology, for alkaloid production, 40, 1 (1991) Plant systematics, 16, 1 (1977) Pleiocarpa alkaloids, 8, 336 (19651, 11, 205 (1968) Polyamine alkaloids, 22, 85 (1983) Pressor alkaloids, 5 , 229 (1955) Protoberberine alkaloids, 4, 77 (1954),9, 41 (1967), 28,95 (1986) transformation reactions of, 33, 141 (1988) Protopine alkaloids, 4, 147 (1954), 34, 181 (1989) Pseudocinchoma alkaloids, 8,694 (1965) Purine alkaloids, 38, 226 (1 990) Pyridine alkaloids, 1, 165 (1950), 6, 123 (1960), 11,459 (1968), 26, 89 ( 1985) Pyrrolidine alkaloids, 1,91 (1950), 6, 31 (1960), 27,270 (1986) Pyrrolizidine alkaloids, 1, 107 (1950), 6, 35 (1960), 12, 246 (1970), 26, 327 (1985)

Quinazolidine alkaloids, see Indolizidine Alkaloids Quinazoline alkaloids, 3, 101 (1953), 7, 247 (1960), 29, 99 (1986) Quinazolinocarbolines, 8,55 (1965),21,29 (1983) Quinoline alkaloids related to anthranilic acid, 3, 65 (1953), 7,229 (1960), 17, 105 (1979), 32,341 (1988) Quinolizidine alkaloids, 28, 183 (1985) Rauwolfia alkaloids, 8, 287 (1965) Reissert synthesis of isoquinoline and indole alkaloids, 31, 1 (1987) Reserpine, chemistry, 8, 287 (1965) Respiratory stimulants, 5 , 109 (1955) Rhoeadine alkaloids, 28, 1 (1986)


Sulumandru group, steroids, 9, 427 (1967) Sceletium alkaloids, 19, 1 (1981) Secoisoquinoline alkaloids, 33, 23 1 (1988) Securinega alkaloids, 14,425 (1973) Senecio alkaloids, see Pyrrolizidine alkaloids Simple indole alkaloids, 10,491 (1967) Simple indolizidine alkaloids, 28, 183 ( I 986), 44, 189 (1993) Sinomenine, 2,219 (1952) Solanum alkaloids chemistry, 3, 247 (1953) steroids, 7,343 (1960), 10, 1 (1967), 19,81 (1981) Sources of alkaloids, 1, 1 (1950) Spectral methods, alkaloid structures, 24,287 (1985) Spermidine and related polyamine alkaloids, 22,85 (1983) Spermine and related polyamine alkaloids, 22, 85 (1983) Spirobenzylisoquinolinealkaloids, 13, 165 (1971),38, 157 (1990) Sponges, isoquinolinequinone alkaloids from, 21, 55 (1983) Stemona alkaloids, 9,545 (1967) Steroid alkaloids Apocynaceae, 9,305 (1967),32,79 (1988) Buxus group, 9, 305 (1967), 14, 1 (1973), 32,79 (1988) Holarrhena group, 7,319 (1960) Salamandra group, 9,427 (1967) Solanum group, 7,343 (1960), 10, 1 (1967), 19,81 (1981) Veratrum group, 7 , 363 (1960), 10, 193 (1967), 14, 1 (1973), 41, 177 ( 1992) Stimulants respiratory, 5, 109 (1955) uterine, 5, 163 (1955) Structure elucidation, by X-ray diffraction, 22, 51 (1983) Strychnos alkaloids, 1,375 (part 1, 1950), 2,513 (part 2, 1952), 6, 179 (1960), 8,515, 592 (1965), 11, 189 (1968), 34,211 (1989), 36, 1 ( 1989) Sulfur-containingalkaloids, 26, 53 (1983, 42, 249 (1992) Synthesis of alkaloids, Enamide cyclizations for, 22, I89 (1983) Lead tetraacetate oxidation in, 36,70 (1989) Tabernaemontana alkaloids, 27, 1 (1983) Taxus alkaloids, 10, 597 (1967), 39, 195 (1990) Thailand, alkaloids from the plants of, 41, 1 (1992) Toxicology, Papaveraceae alkaloids, 15, 207 (1975)

37 I

372

CUMULATIVE I N D E X OF TITLES

Transformation of alkaloids, enzymatic microbial and in uitro, 18, 323 (1981) Tropane alkaloids biosynthesis of, 44, 115 (1993) chemistry, 1,271 (1950), 6, 145 (1960), 9,269(1967), 13, 351 (1971), 16,83 (1977), 33,2 (1988), 44, I (1993) Tropoloisoquinoline alkaloids, 23, 301 (1984) Tropolonic Colchicurn alkaloids, 23, 1 (1984), 41, 125 (1992) Tylophora alkaloids, 9, 517 (1967) Uterine stimulants, 5 , 163 (1955) Veratrum alkaloids cevane group of, 41, 177 (1992) chemistry, 3, 247 (1952) steroids, 7, 363 (1960), 10, 193 (1967), 14, 1 (1973) Vinca alkaloids, 8,272 (1965), 11,99 (1968), 20,297 (1981) Voacanga alkaloids, 8, 203 (1963, 11,79 (1968) X-ray diffraction of alkaloids, 22, 51 (1983) Yohimbe alkaloids, 8, 694 (1965), 11, 145 (1968), 27, 131 (1986)

INDEX

Acetoacetate, as precursor of hyoscyamine and hygrine. 141-142 ( + )-6P-Acetoxynortropane, He and Brossi synthesis, 87 I -Acetylcarbazole, 286 Aflavazole, 316-317 Agmatine, 174 L-Alanine, in monomorine I synthesis, 193-195 Aliphatic acids, esters, biosynthesis, 156-158 Allopumiliotoxin A alkaloids, 199-201 Allopumiliotoxins, total synthesis, 216-219 Amine precursors, feeding studies, 169- 170 Amphibians, indolizidine alkaloids from. 196-220 Anhydroecgonine methyl ester, Davies synthesis. 81-82 Anthocercoideae, tropane alkaloids in, 38-44 Anti-inflammatory properties, carbazole alkaloids. 357-358 Antimicrobial properties, carbazole alkaloids, 353-354 Antitumor alkaloids, 323-324, 354 Antiviral activity, carbazole alkaloids, 355 Ants, indolizidine alkaloids from, 190-196 Arcyriaflavin-B, 3 17-319 Arcyriaflavin-C, 317-319 Arginine decarboxylase, activity changes, 176 Aromatic tropane esters, structures, 118 Atropine demethylation, 89, 91 photocyanation, 91 Atropine esterase, activity, 167 Atropoideae, tropane alkaloids in, 56-63 8-Azabicyclo[3.2. Iloctan-8-one, asymmetric a-ketonic cleavage, I 93- 194 373

Backvall synthesis, tropine, pseudotropine. scopine, and pseudoscopine, 78-79 Baogongteng A Jung et d.synthesis, 85-87 Xiang c/ a / . synthesis, 84, 86 Bathgate and Malpass syntheses, tropane alkaloids, 80-81 Belladonnines, structure, 22 Benzoylecgonine ethyl ester, synthesis, 88 3P-Benzoyloxytropane, thermal degradation, 89-90 N-Benzylnortrop-6-ene. Bathgate and Malpass synthesis, 80-81 Benzyltropanes disubstituted, 14-15 substituted, 14 Biogenesis, carbazole alkaloids, 35 1-352 Biscarbazole alkaloids, 332-348 synthesis. 347-348 Bis-7-hydroxygirinimbine-A,346-347 Bis-7-hydroxygirinimbine-B, 346-347 Bismurrayafoline-A, 333-334 Bismurrayafoline-B, 334-335 Bismurrayafoline-C, 339-340 Bismurrayafoline-D, 339-340 Bismurrayafolinol, 335 Brassicaceae, tropane alkaloids in, 32

Carazostatin, 288-290 Carbazole, 258 Carbazole alkaloids, 257-360; see also Biscarbazole alkaloids anti-inflammatory properties, 357-358 antimicrobial properties. 353-354 antitumor activity, 354-355 antiviral activity, 355 biogenesis, 351-352 cardiovascular-modulating activity, 355-356

374

INDEX

central nervous system activity, 356-357 hexacyclic alkaloids, 3 14 hexacyclic base synthesis, 331-332 hexa- and octacyclic indolocarbazoles, 317-331 infrared spectra, 349 mass spectra, 350 modulation of enzyme activity, metabolism, and allergic reactions, 358-359 NMR spectra, 349-350 occurrence, 258-262 penta- and hexacyclic alkaloids, 315-317 tetracyclic alkaloids, 297-3 14 from higher plants, 297-306 optical properties transformation, 3 I3 from Streptomyces, 306-310 synthesis, 310-312 transformations, 312-314 tricyclic alkaloids from higher plants, 258-283 from non-plant sources, 283-290 synthesis, 290-297 tumor-promoting activity, 354-355 ultraviolet absorption spectra, 349 X-ray crystallography, 350-35 I Carbazole-3-carboxylic acid, 273 Carbazole-3-methylcarboxylate,272-273 Carbazomycin, 294-295 Carbazomycin-A, 290-29 I Carbazomycin-B, 290-291 Carbazomycin-C, 286 Carbazomycin-D, 287 Carbazomycin-G, 288 Carbazomycin-H, 288 Carbazomycinal, 287 Carbofuran, acute intoxication, 98 Carboxytropanes, substituted, 13-14 Cardiovascular-modulating activity, carbazole alkaloids, 355-356 Carprofen anti-inflammatory activity, 358 antiviral activity, 355 Castanospermine, 239-249 stereoisomers, 240 synthesis based on intramolecular cyclization, 243-244 based on stereoselective reduction of cyclic ketone, 243-245

chemoenzymatic avenue, 246-248 double cyclization of epoxy amino ester, 240-242 from glucuronolactone, 242-243 noncarbohydrate starting materials, 245-247 stereoselective, 241-242, 248-249 total, 240-241 unnatural enantiomer, synthesis, 244-246 Central nervous system, carbazole alkaloid activity, 356-357 Cestroideae, tropane alkaloids in, 44-45 3-Chlorocarbazole, 290 6-Chlorohyellazole, 284-285 Chrestifoline-A, 338 Chrestifoline-B, 342 Chrestifoline-C, 343-344 Chrestifoline-D, 334 Clausenapin, 274-275 Cocaine biosynthesis, 92, 94, 142 pharmacology, 98-99 thermal degradation, 90

Datum strnrnonium alkaloid degradation, 165-166 tropane alkaloids, biosynthesis and flux, 129, 172-174 Datureae, tropane alkaloids in, 46-55 Davies synthesis, tropane alkaloids, 81-82 Deacetylkinamycin-C, 3 10 Degradation thermal, tropane alkaloids, 89-90 tropeines, 164-168 2,I'-Dehydrohygrine. biomimetic conversion of hygrine to, 144-145 6.7-Dehydrohyoscyamine. 163 4-Demethoxycarbazomycin-A, synthesis, 294-296 Demethylation, tropane alkaloids, 89-9 1 0-Demethylmurrayanine, 271 DL-a-Difluoromethylarginine, effect on putrescine biosynthesis, 132-133 DL-a-Difluoromethylornithine, effect on putrescine biosynthesis, 132-133 Dihydropyranotropanes, 16-17 Dihydroxygirinimbine, 298

INDEX

I ,2-Dihydroxyindolizidines,228-232 Dihydroxynortropanes, 18 Dihydroxytropanes, distribution, 77-78 Drrboisiu, tropane alkaloid biosynthesis, 129-1 30

Ecgonine methyl ester, formation, 142 Ekebergenine, 278-279 Elncwcurpris alkaloids, 221-224 Elaeokanines. total synthesis, 221-224 Epoxytropanes, substituted, 13 Erythroxylaceae, tropane alkaloids in, 34-38 Euchrestine-A. 275 Euc hrestine-B, 275-276 Euchrestine-C, 276 Euchrestine-D. 276-277 Euchres t ine- E. 277 Euphorbiaceae, tropane alkaloids in, 32 Eustifoline-B, 302 Eustifoline-C. 278 Eustifoline-D, 297

bFerruginine. Davies synthesis. 81-82 3-Formylcarbazole, 267 3-Formyl-7-hydroxycarbazole. 267 3-Formyl-6-methoxycarbazole, 269 Furostifoline, 297 Furuya synthesis, tropane alkaloids, 83-85

(2

Girinimbine, photochemical transformation, 3 13-3 14 Glycomaurin, 302 Glycomaurrol, 275 Glycozolidal, 271 Glycozolidine. 293 Glycozoline, synthesis, 292-293 Grahamine. 13C-NMR spectroscopy, 96-97

Harper approach. tropane alkaloids, 88 He and Brossi synthesis. ( + )-6P-acetoxynortropane, 87

375

Heptazolicine, 303-304 6-Hydroxyhyoscyamine epoxidase, 163 I-Hydroxyindolizidines. 228-232 Hydroxyltropanols, 164 2-Hydroxy-3-methylcarbazole, 263. 294 I -Hydroxynortropopane skeleton, Lallemand synthesis, 83-84 3a-H ydrox ytropane demethylation. 89-90 photocyanation, 91 2a-Hydroxytropinone. Moriarty synthesis, 83-84 Hyellazole, 283-285 synthesis, 294-295 Hygrine acetoacetate as precursor. 141-142 biomimetic conversion to tropinone or 2,1 ‘-dehydrohygrine, 144-145 isomers. as precursors of tropane alkaloids, 143- I44 Hyoscine hyoscyamine conversion to, 160-164 production by tissue cultures, 120-127 structure, I18 Hyoscyamine acetoacetate as precursor, 141-142 biosynthesis, 92-93, 158-159 tropic acid effect, 169. 171 conversion to hyoscine, 160-164 production by tissue cultures. 120-127 structure, I18 Hyoscyamine 6P-hydroxylase. SUbStrdte specificity. 161- I62 H v o s c y m r r s nlbrrs, N-methylputrescine oxidase, kinetic properties, 137-138 H.voscymrrs species, tropane alkaloid biosynthesis, 128

lndole carbazole dimer. 332-333 Indolizidine alkaloids. 189-250 from amphibians, 196-220 structure, 196-20 1 synthesis, 202-220 from ants, 190-196 diepoxides, enantiomer synthesis, 206-208 3,5-disubstituted, 197-198 enantiomer synthesis, 205-206

376 Elaeocarpus alkaloids, 221-224 ( - )-enantiomer synthesis, 206-209 ( + )-enantiomer synthesis, 209-21 I hydroxylated, 228-249 ( + )-Indolizidine 195B, total synthesis, 203-205 I ,2-lndolizidinediol, 231-232 Indolocarbazoles, hexa- and octacyclic, 317-331 Infrared spectra, carbazole alkaloids, 349 Isomahanine, 303 Isomurrayafoline-B, 274 fmns(3,5)-lsoxazolidine, 192-193

Jabroseae, tropane alkaloids in, 46 Jung et a / . synthesis, baogongteng A, 85-87

Ke toanh ydrokinamycin, 309 Kinamycin-A, 307-308 Kinamycin-B, 308 Kinamycin-C, 306-307 antitumor activity, 354 Kinamycin-D, 308 Kinamycin-E, 309 Koenoline, 266-267 synthesis, 290, 292

Lallemand synthesis, I-hydroxynortropopane skeleton, 83-84 Lansbury synthesis, tropane alkaloids, 82-83 Leete and Kim synthesis, tropane alkaloids. 82-83

Mahanimbine cyclomer formation in, 312-313 photochemical transformation, 3 13-314 Mann synthesis, oscine, 87-88 Mass spectrometry carbazole alkaloids, 350 tropane alkaloids, 96-97

INDEX

Metabolite tunneling, in putrescine biosynthesis, 133- 134 6-Methoxycarbazole-3-rnethylcarboxylate, 273 6-Methoxycarbazomycinal, 287-288 7-Methoxyheptaphylline, 279-280

N-Methoxy-3-hydroxymethylcarbazole, 269

2-Methoxy-3-methylcarbazole,263 7-Methoxy-O-methylmukonal, 270 7-Methoxymukonal, 270 7-Methoxymurrayacine, 302-303 6-Methoxymurrayanine, 270-271 1-Methylcarbazole, 285-286 3-Methylcarbazole, 293 N-Methylcarbazole, tumor-promoting activity. 354-355 8-Methylindolizidines. 5-substituted, 197-198 synthesis, 21 1-213 0-Methylmukonal, 269-270 N-Methylpelletierine. synthesis, 143 N-Methylputrescine, 175 biosynthesis, 130- 13 I N-Methylputrescine oxidases, kinetic properties, 137-138 N-Methylpyrroliniurn conversion of putrescine to, 134-140 conversion to tropinone, 140- 145 Monomorine I asymmetric a-ketonic cleavage of 8-azabicyclo[3.2.1Iloctan-8-one. 193- 194 synthesis from L-alanine, 193-195 asymmetric, 190-192 enantioselective total, 192-193 from (S)-pyroglutamic acid, 195 Moriarty synthesis, 2a-hydroxytropinone. 83-84 Mukolidine, 265-266 Mukoline, 265-266 Mukonal, 269 Mukonicine, 301 Mukonine, synthesis, 290-291 Murrafoline, 347 Murrafoline-B, 340 Murrafoline-C, 344 Murrafoline-D, 341 Murrafoline-E, 341 Murrafoline-F, 336

INDEX

Murranimbine, 344-345 Murrastifoline-A, 337-338 Murrastifoline-B, 337-338 Murrastifoline-C. 343 Murrastifoline-D. 34 1-342 Murrastifoline-E, 342 Murrayafoline-A, 262, 293 Murrayafoline-B, 273-274 Murrayaline-A, 264-265 Murrayaline-B, 271-272 Murrayaline-C. 272 Murrayaline-D. 279 Murrayanol, 277-278 Murrayaquinone-A, 280 Murrayaquinone-B, 280-283 Murrayaquinone-C, 283 Murrayaquinone-D, 283 Murrayastine. 263-264 Murrayazoline, 3 14 Murrayazolinol, 3 14

Nicandreae, tropane alkaloids in, 56 Nicoriunu rabricum, N-methylputrescine oxidase, kinetic properties, 137-138 Nicotine, biosynthesis, 172 NMR. see Nuclear magnetic resonance Norgirinimbine, synthesis, 312 Nuclear magnetic resonance I 'C carbazole alkaloids, 350 tropane alkaloids, 95-97 'H carbazole alkaloids, 349-350 tropane alkaloids, 95-96

Olacaeae, tropane alkaloids in, 38 Optical activity, tropane alkaloids, 77-78 Organ tissue cultures, tropane alkaloid biosynthesis, 119-120 Dcitirrci sfrumonium. 129 Dtrhoisici, 129-130 Hyosc-yumirs. 128 Ornithine decarboxylase. activity changes. I76 Oscine Mann synthesis. 87-88 NMR spectroscopy, 95-96

377

N-Oxidation, tropeines, 168 3-Oxotropane demethylation, 89. 91 photocyanation, 91 structure, 17 Oxydimurrayafoline, 335-336

Pharmacology. tropane alkaloids. 97-99 Phenylalanine, metabolism, 151-152 Phenyllactic acid, biosynthesis. 151-154 Phenylpyruvic acid, 152, 154 Photocyanation, tropane alkaloids, 89. 91 Piperidine, cis-2,6-disubstituted, 195-196 Plants, containing tropane alkaloids, 4-5 Prekinamycin, 308-309, 31 1 Proteaceae, tropane alkaloids in, 32-33 Protein kinase C inhibitors K-252a, 330-331 K-252b. 330-331 K-252~.319-320 K-252d, 320 Pseudoscopine, Backvall synthesis, 79-80 Pseudotropine acetylation, 156 Backvall synthesis, 78-79 biosynthesis, 146-150 Pumiliotoxins A, 199-201 synthesis, 215-216 Pumiliotoxins D, enantioselective synthesis. 217-218, 220 Putrescine biosynthesis, 130- I34 enzyme inhibitor effect, 132-133 labeled precursor incorporation. 132 metabolite tunneling, 133-134 conversion to N-methylpyrrolinium. 134-140 formation. 174 Putrescine N-methyltransferase biosynthesis regulatory role, 172 induction, 174 Pyranotropanes, structure, I6 Pyrayafoline-A, 298-299 Pyrayafoline-B, 299-300 Pyrayafoline-C, 300 Pyrayafoline-D, 300 Pyrayafoline-E. 301 Pyrayaquinone-A, 304 Pyrayaquinone-B. 304-305

378

INDEX

Pyrayaquinone-C, 305-306 acid, in monomorine I synthesis, 195

( S)-Pyroglutamic

Rebeccamycin, 320-322 Rhizophoraceae, tropane alkaloids in, 33 Rincazole, 357

Schizanthines, 21, 23 Scopadonnines, 22-23 Scopine, Backvall synthesis, 79-80 Scopolamine biosynthesis, 94-95 NMR spectroscopy, 95-96 pharmacology, 99 Sikabaceae, tropane alkaloid degradation, I65 Slaframine. 223-227 asymmetric synthesis, 224-226 enantioselective synthesis, 226 synthesis via radical cyclization, 226-227 Solandreae, tropane alkaloids in, 55-56 Solaneae, tropane alkaloids in. 45-46 Speckamp synthesis, tropane alkaloids, 84-85 Staurosporine, 324-328 Swainsonine, 233-239 noncarbohydrate route, 237-238 stereoisomers, 238-239 synthesis enantioselective, 234-236 enantiospecific, 233 from hydroxy lactam, 236-237 from D-mannose, 234-235 from tartarimide, 238-239

Tan-999, 330 Tan-I030A, 328-330 I ,6,7,8-Tetrahydroxyindolizidines, 249 Tetrahydroxynortropanes, 19 8-Thiabicyclo[3.2. Iloctan-3-one, 149- 150 Tiglic acid, biosynthesis, 154-155 Tigloidine, synthesis, 157 /3-Tigloxyltropane, synthesis, 157

3-Tigloylox ytropane formation. I7 1- 172 synthesis, 159-160 Trihydroxynortropanes, 18 Tropane alkaloids, 1-100 acyl group structures, 26-31 in Anthocercoideae, 38-44 in Atropoidea, 56-63 biosynthesis, 92-95 day length effect, 178 formation of tropanes from amino acids, 116-117 organ tissue cultures, 119-130 pathway regulation biochemical level, 169-176 whole-plant level, 177-180 temperature effects, 178 water stress effect, 179 in Brassicaceae, 32 in Cestroideae, 44-45 chemotaxonomy of plants, 65-77 in Concoculaceae. 63-65 in Datureae, 46-55 demethylation. 89-91 disubstituted, structures, 9-12, 14-15 in Erythroxylaceae, 34-38 in Euphorbiaceae, 32 industrial preparation, 99- 100 in Jabroseae. 46 mass spectrometry, 96-97 medicinal use. 116 3cu-monosubstituted, structures, 7-8 3P-monosubstituted, structures, 9 in Nicandreae, 56 NMR spectra, 95-97 numbering system, 2 in Olacaceae, 38 ontogeny of accumulation, 177 optical activity, 77-78 pharmacology, 97-00 photocyanation. 89. 91 plant origin, 66-76 plants containing, 4-6 potassium stress effect, 179 in Proteaceae, 32-33 in Rhizophoraceae, 33 ring system, 2 in Solandreae, 55-56 in Solaninae, 45-46 in Solanoideae, 45-46

INDEX

structures, 6-31 synthesis, 78-88 thermal degradation, 89-90 trisubstituted, structures, 12 Tropeines biosynthesis, 155-160 acidic moieties, 151-155 esters of aliphalic acids, 156-158 hyoscyamine and aromatic esters, 158-160 degradation and oxidation, 164-168 metabolism, 160-164 Tropic acid biosvnthesis. 15 1- 154 effect on hyoscyamine production, 169, 171 Tropine acetylation, 156-157 Backvall synthesis, 78-79 biosynthesis, 92-93, 146-150 feeding studies, 169-170 Tropinone biosynthesis, 92-93, 134-145 N-methylpyrrolinium conversion to tropinone, 140-145

3 79

putrescine conversion to N-methylpyrrolinium, 134- 140 Lansbury synthesis, 82-83 Tropinone reductase I , 146-148 Tropinone reductase 11, 147-150 Truxillines, 25 Tubingensin-A, 3 15-316 Tubingensin-B, 316 Tumors, promotion by carbazole alkaloids. 354-355

UCN-01, 331 Ultraviolet absorption spectra, carbazole alkaloids. 349

Xiang et a / . synthesis, boagongteng A. 84, 86 X-ray crystallography, carbazole alkaloids. 350-35 I


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The Alkaloids: Chemistry and Pharmacology, Volume 44

The Alkaloids Chemistry and Pharmacology, Volume 27

The Alkaloids: Chemistry and Pharmacology, Volume 51

The Alkaloids: Chemistry and Pharmacology, Volume 22

The Alkaloids: Chemistry and pharmacology Volume 38

The Alkaloids: Chemistry and Pharmacology, Volume 15

The Alkaloids: Chemistry and pharmacology Volume 34

The Alkaloids: Chemistry and Pharmacology, Volume 37

The Alkaloids: Chemistry and Pharmacology, Volume 40

The Alkaloids: Chemistry and Pharmacology, Volume 35

The Alkaloids: Chemistry and Pharmacology, Volume 52

The Alkaloids: Chemistry and Pharmacology, Volume 29

The Alkaloids: Chemistry and pharmacology Volume 32

The Alkaloids Chemistry and Pharmacology, Volume 04

The Alkaloids: Chemistry and Pharmacology, Volume 30

The Alkaloids: Chemistry and Pharmacology, Volume 43

The Alkaloids: Chemistry and Pharmacology, Volume 49

The Alkaloids: Chemistry and Pharmacology, Volume 37

The Alkaloids: Chemistry and Pharmacology, Volume 41

The Alkaloids: Chemistry and Pharmacology, Volume 36

The Alkaloids: Chemistry and Pharmacology, Volume 31

The Alkaloids: Chemistry and pharmacology volume 26

The Alkaloids: Chemistry and pharmacology volume 28

Alkaloids: Chemistry and Pharmacology, Volume 12

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The Alkaloids: Chemistry and Pharmacology, Vol. 21

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