Aliphatic and Related Natural Product Chemistry Volume 1

A Review of the Literature Published during 1976 and 1977

By F.D. Gunstone

The Royal Society of Chemistry

Copyright © 1979 The Chemical Society
All rights reserved.
ISBN: 978-0-85186-642-0

Contents

Chapter 1 Natural Acetylenic and Olefinic Compounds excluding Marine Natural Products By V. Thaller, 1,
Chapter 2 Marine Aliphatic Natural Products By R. E. Moore, 20,
Chapter 3 Acyclic Terpenoids By D. H. Grayson, 68,
Chapter 4 Insect Pheromones and Related Behaviour-modifying Chemicals By R. Baker and D. A. Evans, 102,
Chapter 5 Olefinic Microbial Metabolites including Macrocyclic Compounds By R. C. F. Jones, 128,
Chapter 6 Chemistry of the Prostaglandins By P. R. Mar sham, 170,
Chapter 7 Fatty Acids By F. D. Gunstone, 236,
Chapter 8 Lipids By A. K. Lough, 263,
Author Index, 293,

CHAPTER 1

Natural Acetylenic and Olefinic Compounds excluding Marine Natural Products

BY V. THALLER

1 Introduction and Scope of the Chapter

This Report covers developments in the chemistry of natural acetylenes and olefins during 1976 – 7 and can be regarded as part-successor to G. Pattenden’s Chapters 3 in the Specialist Periodical Reports on Aliphatic Chemistry Volumes 2 – 5 for the years 1972 – 5. Whilst the scope of the acetylene part is reduced only by the omission of the relevant marine products, most of the olefin part is covered now by other chapters of this volume. The material discussed has been collected for ease of orientation under several sub-headings, although this sometimes leads to repetition of references and double citations.

2 Natural Acetylenic Compounds

Introduction. — The very rapid expansion which has occurred in this field since the early fifties (7 compounds were known in 1950, over 700 are known today) has slowed down considerably. By far the greatest number of natural acetylenes belongs to the group of secondary metabolites known as natural polyacetylenes. They have been shown to originate in Nature from C18 fatty acids by pathways which include a combination of desaturation, chain shortening, oxidation, rearrangement, cyclization, and other funtionalization processes. The many imaginable permutations have certainly not been exhausted, but their detection and isolation are more sporadic. Although the general principles of polyacetylene biogenesis are thought to be understood, many details still wait to be confirmed, not least the biogenesis of the triple bond itself. The reason for polyacetylene formation, their role and fate in the economy of the plants, higher and lower, which produce them, still needs elucidation.

Bohlmann, who with his co-workers contributed more than any other single group to the development of the natural acetylene field, always conscious of the chemotaxonomic implications of his work, has moved even further in this direction. He is now involved in a more general analysis of the secondary metabolites of species, mostly Compositae, the classification of which leaves open some doubts and investigates the contribution chemotaxonomy can make to their reclassification. Thus Bohlmann’s long polyacetylene series increased during the two years under review by only eight publications (parts 237 – 244), but some information on polyacetylenes appears continuously in his series on natural terpenes, coumarins, etc.

The book on ‘Naturally Occurring Acetylenes’ forms an invaluable basis for the study of this field. Pattenden’s reports have been keeping it up-to-date, and this Report continues this trend.

New Polyacetylenes from Plants. — With the exception of the Anonaceae species and some Korean Umbelliferae species, which were screened for polyacetylenes, all plants investigated belong to various tribes of the Compositae family. The isolation of the sixteen C21 diynes and diynenes (1) – (4) has been reported from the roots and, to a lesser extent, the bark of the tree Alphonsea ventricosa Hook F. and Th. (Anonaceae family), a native of Assam. The discovery of C21 poly acetylenes, the longest poly acetylene chain found thus far in Nature, in the Anonaceae species has already been mentioned, but details of the structures were not available. These consist of all possible permutations of four distal C6 fragments (R1) and four proximal oxygenated C4 fragments (R2) around a central C11 diyne. The root extract was readily separated into the four groups (la – d), (2a – d), (3a – d), and (4a – d), and of these only the first could be further separated into (1a,b) and (1c,d). 1H n.m.r., aided by shift reagents, and low and high resolution mass spectra indicated structures for the metabolites present in each group. A series of chemical transformations which were carried out on the mixtures enabled the separation and identification of the four distal C6 fragments, and interconversions of the mixtures established their relationships firmly. Pathways for the formation of these polyacetylenes have been proposed: the preferred one is a C18 + C3 [right arrow] C21 chain elongation involving the condensation of the known (Santalaceae and Olacaceae) C18 acids (5a – d) with pyruvate. The analogy in the structure of the oxygenated proximal part of the C21 metabolites with those of the C17 metabolites from Persea gratissima seeds, the Lauraceae and Anonaceae being relatively closely related, stimulated the authors to speculate about a similar C14 + C3 pathway for the C17 compounds.

The presence of thirty nine C13 – C17 poly acetylenes was established in the roots and green parts of eight representatives of the genus Dahlia. All contained varying amounts of poly acetylenes, but only the C13 hydrocarbon (6) was found to be present in all eight of them. The new C16 alcohol (7) and its acetate (8) were isolated from D. scapigera (A. Dietr.) Link and Otto var. scapigera f. scapigera; the alcohol was synthesized. The new C13 diol (9) and its diacetate (10), the C14 diol (11) and the diacetate (12), and the C17 alcohol (13) and the corresponding acetate (14) were isolated from the garden varieties. The spectra of the metabolites and simple transformation products established their structures. The alcohol (13) was synthesized.

Two more benzenoid polyacetylenes have been isolated from Artemisia capillaris Thunb. Norcapillen (15) was found to represent 0.1% of its essential oil and neocapillen (16) was identified as a minor component in the root extract. Spectral analysis, hydrogenation, and synthesis were used in both instances.

Known polyacetylenes were isolated from A. monosperma (from Israel) and A. dracunculus L. (seeds from Tashkent). In the roots of the latter, the acetylenic isocoumarin (17) isolated from other A. dracunculus specimens gave place to the olefin (18), an occurrence which might be of biogenetic interest.

A few of Bohlmann’s publications appear to represent the rounding off of his intensive investigation of South African Compositae. Thus, amongst several known thiophene acetylenes, the new thiophene diol (19) was isolated from Platicarpa glomerata: its structure followed from spectral data obtained from the metabolite and its MnO2-oxidation product. The majority of species Bohlmann has analysed recently seem, however, to originate in the Americas. Several new thiophene acetylenes (terthienyls are included on biogenetic grounds) were found here too and identified by spectral methods. The roots and greenery of the Mexican Compositae Dyssodia anthemidifolia Benth. contained the terthienyls (20) and (21), the latter being obtained pure for the first time, and the green parts of D. setifolia (Lag.) Rob. yielded the dithienyl acetylenes (22), (23), (24), and (25). The roots of D. acerosa contained in addition to several known thiophenes, the new dithienyl diyne (26) whilst D. papposa (Vent.) Hitchc. yielded only known polyacetylenes. A score of known thiophenes were also isolated from the roots of Haploestes gregii var. texana amongst them the two new metabolites (27) and (28), the former already known synthetically.

New polyacetylenic sulphoxides and sulphones have also been isolated and are always accompanied in the plants by many known polyacetylenes. From the roots of the Texan Baileya multiradiata Harv. et Gray. the sulphoxide (29) was isolated. Very little of the natural product was available and its stereochemistry was established by synthesizing the cis- and trans-isomers from the known sulphides. The greenery of the Mexican species Coreopsis parvifolia Blake (Sekt. Electra) contained the isomeric sulphoxides (30) and (31) and the sulphone (32). The latter is now known to occur along with the cis-isomer in the roots of Helenium tenuifolium Nutt.

C17 poly acetylenes, amongst them dehydro falcarinone and the new aldehyde (34) were isolated from the roots of the Mexican Heliantheae species Calea integrifolia Hemsl. In addition to’spectral identification, the new metabolite gave, on NaBH4 reduction, the corresponding known C17 alcohol.

A mixture of the related aldehydes (34) and (35) was isolated from the roots of the South African species Senecio deltoides Less., the structures being assigned from spectral data. The analysis of further Senecio species established the presence of a considerable number of known polyacetylenes in many of the species investigated. The green parts of S. chrysanthemoides D.C. contained the new acetylenic angelicate (36), identified by its spectra and by transesterification to methyl angelicate.

From the roots of the Compositae Jungia spectabilis D. Don., a native of Ecuador, the new C15 polyacetylenes (37) and (38) were isolated and identified by their spectra. They represent the first Compositae polyacetylenes in which the terminal -CH=CH2, originally the proximal half of the C18-precursors, is absent, presumably hydrogenated.

The Cynereae (Compositae) species Serratula wolfii Andrae was found to contain a series of known C13 – C17 polyacetylenes and the two pairs of new epimeric C15 polyacetylenes (39) and (40). The structures were established spectroscopically, primarily by the 270 MHz 1H n.m.r. spectra, and confirmed by the synthesis of the methyl ethers of the pair (40).

The stereochemistry of the new natural product (41) from Solidago altissima L. was established by spectral comparison with the two synthetic 2-methyl-but-2-enoates. Atractylodinol (42) and its acetate (43) have been isolated in addition to atractylodin from Atractylodes lancea de Condolle var. Chinensis Kitamura; the structures were elucidated by spectroscopy and chemical transformations. Both were piscicidal.

Wyerone epoxide (44) has been isolated and shown to be the third component of the multiple phytoalexin response of the broad bean, Vicia faba L., to fungal (Botrytis) infection. Its structure was confirmed by comparison with the synthetic epoxide obtained from wyerone and m-chloroperbenzoic acid.

The C13 enetriynediene from Carthamus tinctorius L. has been shown to exist in Nature as a mixture of the isomers (45) and (46) in a 83 : 17 ratio which is photoisomerized to an equilibrium mixture of 37 : 63. The two isomers have now been prepared pure (1H n.m.r.) by high pressure liquid chromatography on reversed phase. The hydrocarbon mixture is strongly nematocidal (for the test Apheleuchoides besseyi was used).

Known Polyacetylenes from Plants. — As mentioned above, known polyacetylenes have been regularly detected along with new ones. In many species analysed for the first time only the presence of known polyacetylenes has been observed. As the allocation of several of these species to genera and tribes appears to be in doubt, the polyacetylene containing species themselves are, with few exceptions, listed alphabetically; formulae and names of the polyacetylenes which have been detected have on the whole been omitted. Species already quoted in the section dealing with new poly acetylenes have not been cited again.

Known polyacetylenes have been found in the following Compositae species: Ageratina exertovenosa (Klatt) King et Rob. and A. glabrata (HBK) King et Rob.; Ambrosia cumanensis, Arctotis aspera L., A. repens Jacq., and A. revoluta Jacq.; Ayapana ecuadorensis King et Rob.; Berkheya radula (Harv.) De Willd., B. bipinnatifida (Harv.) Roessler, and B. rhapontica (DC) Hutch, et Burtt Davy ssp. platyptera (Harv.) Roessler (all Berkheya species contained thiophene acetylenes); Calea zacatechichi Schlecht. and C. scabra (Lag.) B. L. Robinson; Callilepis laureola DC.; Centaurea scabiosa (Centaurea species are ingenious polyacetylene producers; in the species discussed 25 polyacetylenes have been found); Dimorphotheca pluvialis Moench. and D. aurantiaca Hort.; Elephantopus mollis HBK.; Erlangea rogersii S. Moore; Felicia uliginosa (Wood et Evans) Gray Flourensia resinosa Blake and F. cernua DC.; Gymura crepioides; Gynoxys sancto antonii Hieron; Hebeclinum macrophyllum (L.) DC.; Heterotheca inuloides Cass.; Hymenopappus scabiosaeus var. corymbosus; 10 Inula viscosa Ait. (on an earlier investigation, the polyacetylene presence was not detected); Isocarpha oppositifolia (L.) R.B.; the Liabum group from Ecuador (all contain phenylheptatriyne which was found hitherto only in the Heliantheae); Ligularia hodgsoni Hook, f., L. brachyphylla Hand. Mazz., L. dentata (A. Gray) Hara, L. veitchiana Greenm., and L. japonica DC.; Macowania glandulosa N.E. Br. and M. cf. hamata; Melampodium perfoliatum (Carv.) A. Gray; Mutisia coccinea A. St. Hill.; Parthenium hysterophorus, Perymenium equadoricum Blake; Picradeniopsis woodhousei Gray; Pluchea odorata Cass.; Podachaenium eminens; Polymnia fructicosa Benth. and P. pyramidelis Triana; Schistocarpha bicolor Less.; Schkuhria senecioides Ness, and S. pinnata (Lam.) Kuntze; Simsia dombeyana DC.; Stevia serrata Cav. and S. ovata Willd.; Tanacetum tanacetioides (DC) Tzvel.; Tessaria absinthioides (H. et A.) Cabr.; Verbesina angustifolia (Benth.), V. greenmanii Urb., and V. oncophora Rob. et Seat.; twenty Vernonia species all contain very small amounts of tridecapentaynene; Viguiera stenoloba; Wedelia trilobata (L.) Hitch, and W, grandiflora Benth.

Several papers concerned with the screening of Korean plants for polyacetylenes appeared in Korean journals. Although only one author is common to all publications, one paper appears to cover all the species screened and found to contain polyacetylenes. They were detected in the Compositae Aster scaber and Chrysanthemum sibirzcum and the Umbelliferae Angelica decursiva and A. koreana, Heracleum moellendorfii, Peucedanum japonicum, Phellopterus littoralis, and Pleurospermum kamtschaticum. Korean workers also found that fresh Ginseng extracts contained only two polyacetylenes but that their number increased on standing indicating the formation of polyacetylenic artefacts.

Polyacetylenes from Fungi. — The new C8 hydroxy acid (47) has been isolated together with known polyacetylenes from cultures of the fungus Camarophyllus virgineus (Wulfen ex Fr.) Kummer. This belongs to the Hygrophoraceae, a fungal family not previously reported as a polyacetylene producer.

The isolation of five C22 diacetylenes from the sponge Reniera fulva, collected in the Bay of Naples, has been reported. Marine products are dealt with in Chapter 2 of this volume, but the question of chirality allocated to the marine diynol (48) and diynediol (49) requires comment in the context of fungal polyacetylenes. The chiralities of the fungal C7 diynol (50) and the C8 diynediol (51), a transformation product of the fungal C9 triol (52), have been determined by unambiguous chemical transformations. The groups attached to the chiral centres in the two pairs of diynes are identical but for the length of the alkyl chain and the presence of distal double bonds [and bromine in (48)] in the marine products. Both fungal compounds show negative rotations and negative trends in their o.r.d. curves from 589 – 365 nm. Negative rotations at 589 nm have been cited for the marine products and their chiralities have been assigned by Gilbert and Brooks’ gas chromatographic modification of Horeau’s method. The coincidence of the negative rotations itself, on which the authors made no comment, is in no way a sufficient indication for identical chiralities in the two pairs of compounds. This Reporter is, however, a little uneasy on account of this coincidence and feels that the chirality of the two marine alcohols merits further attention.

Non-Polyacetylenic Acetylenes. — Most of these metabolites will certainly appear in other Report-volumes, but they are collected here for the sake of completeness. The structure of rubrynolide (53), a constituent of the trunk wood of the Lauraceae Nectandra rubra (Mez) C. K. Allen, a native of the Amazon Basin, was proposed years ago. The stereochemistry of the compound has now been determined with the help of 1H n.m.r., o.r.d., Horeau’s method, and Hudson’s lactone rule as (2S)(4R) and (2′S); full supporting chemical and spectral evidence is provided.

(Continues…)Excerpted from Aliphatic and Related Natural Product Chemistry Volume 1 by F.D. Gunstone. Copyright © 1979 The Chemical Society. Excerpted by permission of The Royal Society of Chemistry.
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