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Clerodane Diterpenoids

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Clerodane Diterpenoids View Online Clerodane Diterpenoids A. T. Merritt Glaxo Group Research L td., Greenford, Middlesex, U86 OHE S. V. Ley Department of Chemistry, Imperial College, London, S W7 2A Y 1 Introduction 2 Taxonomy 3 Isolation and Elucidation 3.1 Family Annonaceae 3.2 Family Aristolochiaceae 3.3 Family Menispermaceae o.-*Ha., I .- 3.4 Family Portulacaceae 3.5 Family Flacourtiaceae 3.6 Family Cistaceae 3.7 Family Cucurbitaceae OAc 3.8 Family Caesalpinaceae 1‘8 OAc 3.9 Family Leguminosae 3.10 Family Mimosaceae 3.1 1 Family Euphorbiaceae 3. I2 Family Rutaceae 3.13 Family Sapindaceae 3.14 Family Verbenaceae 3.15 Family Labiatae 3.16 Family Scrophulariaceae H 3.17 Family Compositae 3.18 Family Alismaceae 3.19 Family Orchidaceae 3.20 Family Araucariaceae 3.21 Order Jungermanniales 3.22 Order Moniliales 3.23 Family Actinomyces 4 Clerodane Derived Diterpenes 5 Biological Activity 6 Recent Isolations 7 References Downloaded by Texas A & M University on 10 February 2011 with C4 methyl migration Published on 01 January 1992 http://pubs.rsc.org | doi:10.1039/NP9920900243 1 Introduction During the last thirty years, over six hundred and fifty diterpenoids and nor-diterpenoids with the clerodane carbon skeleton (1) have been isolated. Confusion has arisen in the literature over the absolute stereochemistry of the various clerodanes isolated. The revision of the absolute stereochemistry of clerodin (2),l the first member of the clerodane series,2 has led to those compounds with the same absolute stereochemistry as clerodin being termed neo-clerodanes and those compounds enantiomeric to clerodin being termed ent-neo-clerodanes. A further division of the clerodanes has been to cis and trans compounds, depending on the stereochemistry of the decalin ring junction. Biosynthetically, the clerodanes appear to be related to the labdanes, via a series of methyl and hydride shifts. The labdane skeleton (4) is itself derived from geranylgeranylpyrophosphate Trans Cis (3) (Scheme 1),3 although this represents a simplification of the Scheme 1 overall biogenetic route, involving many parallel pathways to yield the multitude of clerodane natural products. The trans clerodanes can arise via a concerted migration Me process to intermediate (9,whilst the cis compounds require a stepwise process, with a ‘pause’ at intermediate (6). This can then lead to either cis or trans compounds, depending on which of the C-4 methyl groups ~nigrate.~This proposed biosynthetic pathway is supported, for example, by the isolation of the partially rearranged labdane compounds chettaphanin (7) from Adenochlaena siamensis (C~mpositae)~and salmantic acid (8) from Cistus laurifolius (Cistaceae).6 243 View Online 244 NATURAL PRODUCT REPORTS, 1992 DIVISION CLASS SUBCLASS ORDER FAMILY GENUS No. Species Annona 1 Monolliales -Annonaceae I_f Xywh 1 Magnollidae porVakhk 2 Arktolochiales -Aristobchiaceae -Akritohxhia 3 Dioscoreojhyilum 1 Ranunculidae -Ranunculales -Menispemaceae-Jk rg;bm 2 1 1 Caryophyllidae -Caryophyllales -Portulaceae -Portulaca 2 Flacourthceae -Casearia 1 Dillenlidae -Violales Cistaceae cistus 4 -E Cucurbitaceae -Whria 1 Caesalpinaceae Har&ic&ia 1 ~~eik~&on1 Legurninosae -Capaha 1 Mirnosaceae -Plathymenia 1 ' R~~idae 15 Euphorbiaceae ZEus 1 Mgno liopsida- Eremocapus 1 Rutaceae Evodia 1 MOM 3 Clerwrendron 8 Carycpterk 1 Verbenaceae Cyanostegk 1 Pityradia 1 Callkarpa 1 - Lamlales Ajuga 6 Teucrium 48 Labiatae Salvia 17 Leonurus 2 Sachys 3 Scutellaria 3 - Scrophulariales -Scrophulariaceae -Linaria 2 --sdidagq 9 - Bacchans 35 -syrrphiqrrapP@ 3 - Conyza 3 4 Downloaded by Texas A & M University on 10 February 2011 - Haplapappus - Asteridae - Swia 3 Acritw@ 2 Published on 01 January 1992 http://pubs.rsc.org | doi:10.1039/NP9920900243 - - Nidoreh 2 Magnoliophyta - Olearia 2 (Angiosperms) - Liatris 2 - Harhvrightia 1 - Bahianthus 1 - Hinterhubera 1 - Aster 1 - Hetewappus 1 - Asterales -Cornpositae Fleisahmannia 3 - Melanpudium 1 - Pulkaria 2 - Goyazianthus 1 - Gochnata 1 - Chrmlaena 2 - Gutienezia 2 - Macowania 1 - Chilbthum 1 - Ageratina 2 - Etpatorium 1 - Viftaciania 1 - Plazia 1 - Rhynchospermum 1 - Grangea 1 - Vanclevea 1 Alismidae -Alkt~~les - Alismaceae -Saginark 1 uliopsida -[ "lii&e Orchidales -Orchidaceae -E-emantha 1 Pinophyta -Cycadopsida Cycadales -Araucariaceae -Araucaria 2 (Gymnosperms) Gymnocolea 1 Bryophyta -Hepaticopsida -Jungermanniidae - Jungermannkles awia 1 Pleuroza 1 Mycota Deuterornycetes Monoliales Okfioden&on 1 Adinornyces Schizophyta -Schizomycetes Actinomycetales - Kitasatoqwrm 1 Scheme 2 View Online NATURAL PRODUCT REPORTS, 1992-A. T. MERRITT AND S. V. LEY 245 Several synthetic approaches to the clerodanes have appeared in the literature, but these have been reviewed elsewhere’ and Table 1 Clerodanes obtained from Annonaceae are beyond the scope of this article. This review will instead Genus - Annona consider the isolation, structural elucidation, and reported Species Compounds Ref. Comments biological activity of the large number of clerodanes reported in the literature. A. coriacea (9), (10) 10 (9) see Compositae Genus - Xylopia Species X. aethiopica (1 1) 11 see Aristolochiaceae 2 Taxonomy Genus - Polyalthia The taxonomic relationships of the clerodane producing plants Species are shown in Scheme 2, to the rank of genera. The scheme is P. longifolia (1 2), (15) 12 (15) see Compositae, based on the system of Cronquist,* extended beyond the X-Ray structure angiosperms by the systems of H~lmes.~The vast majority of P. viridis (1 5) 13 see Compositae clerodanes have been isolated from dicotyledonous plants (the Magnoliopsida), with examples from all but one of the relevant sub-classes. Below sub-class, however, a greater degree of specificity occurs, with only a small fraction of orders and families apparently producing clerodanes. This appears to go against normal taxonomic trends, where one might expect a pyramidal relationship leading down from sub-class to genus. It is possible that the various genera/families developed independently the capacity to biosynthesize the clerodanes, or : the simply that there are a large number of families producing as R yet unisolated clerodanes. The independent development of synthetic ability is sup- (9) R = Me, 3-4 =double ported by the occurrence of the non-dicotyledonous producers, (10) R = C02H, 3-4 = Single with two genera of monocotyledonous species (class Liliopsida), one genus of a gymnosperm, three genera of liverworts (Bryophyta), one genus of fungi (Mycota), and one strain of bacteria (Schizophyta). Although these have only been shown to produce a limited range of clerodanes, their ability to do so, 14 considered alongside the large taxonomic differences, lends support to an independent synthetic development. In the following sections, the individual families will be tabulated, with reference to any family or genera related trends, and they will be considered in the evolutionary order for the I Me Magnoliopsida, as proposed by Cronquist,* reading from top Me to bottom of Scheme 2. Within individual families and genera, however, the species have been grouped to indicate chemical (11) R’=Me, R2=H, X’,X2==0, 13-14=€ similarities of the isolated natural products, or trends in the (12) R’ = CHO, R2 = H, X’ = X2 = H, 13-14 = Z productivity of species, rather than adhering to strict taxonomic (13) R’ = R2 = Me, X1,X2 = =0, 13-14 = E Downloaded by Texas A & M University on 10 February 2011 ordering. (14) R’ = R2 = Me, X’ = OOH, X2 = H, 13-14 = E Published on 01 January 1992 http://pubs.rsc.org | doi:10.1039/NP9920900243 3 Isolation and Elucidation The elucidation of the clerodane structures, and specifically the stereochemical relationship of substituents, has not been consistent in the literature. Several of the compounds have proved suitable for X-ray structural analysis, whilst others have been assigned by extensive spectral and correlation techniques. Many compounds, however, have been presented with only a minimal amount of spectral data to support the structural assignments. Only those compounds established by X-ray techniques have been indicated in the comments in the following tables. In addition, in many cases there is confusion between acidic and ester groupings in the natural products, due to the isolation techniques utilized and readers are advised to refer to the source references for possible further clarification. Finally, any cross family connections are also indicated in the comments section. 3.3 Family Menispermaceae 3.1 Family Annonaceae Four genera are of interest here, giving fifteen clerodanes Three genera have been shown to yield clerodanes, with only (Table 3). Fourteen of these have been shown by chemical and trans compounds being produced, as shown in Table 1. spectral methods to be cis-clerodanes, whereas the other compound remains unassigned. All the compounds contain an unusual fused S-lactone ring at C-8-C-9, incorporating the 3.2 Family Aristolochiaceae C- 1 14-16 side chain. Genus-Aristolochia This genus has been shown to produce open chain C-11-C-16 compounds, often ‘common ’ compounds found in other 3.4 Family Portulacaceae families (Table 2). Clerodanes obtained from Portulaceae are given in Table 4. View Online 246 NATURAL PRODUCT REPORTS, 1992 Table 2 Clerodanes obtained from Aristolochiaceae Genus - Aristolochia Species Compounds Ref. Comments A. galeata (16) populifolic acid 14 see Cistaceae, Compositae (17) see Cistaceae (28) kolavelool see Compositae, Caesalpinaceae (30) kolavenol see Compositae, Caesalpinaceae (3 1) kolavenic acid see Compositae, Caesalpinaceae A. esperanzae
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