Natural Acetylenic and Olefinic Compounds, excluding Marine Natural Products

C. M. SCRIMGEOUR

1 Introduction

This report covers the same topics as does the corresponding chapter in the first volume of this series. The bulk of it is concerned with polyacetylenic and other acetylenic aliphatic natural products while the remainder deals with olefinic compounds not obviously included in the other chapters. The literature coverage is for 1978–9 plus a few earlier reports not previously included.

2 Natural Acetylenic Compounds

Introduction. – This two-year spell has again been one of consolidation rather than dramatic progress. A number of new compounds, mainly related to previously known structures, have been reported. A number of new sources of known compounds have also been reported. Many of these reports concern the physiological role or chemotaxonomic application of acetylenic compounds. Four general reviews about polyacetylenes have appeared, covering the work of the past decade or more. While Bohlmann's output has continued to focus on terpenoid compounds, he still remains the most prolific contributor to this field.

New Polyacetylenic Compounds. — The majority of new compounds are found in species within the family Compositae. A C18 enediynene (1) and the related dihydro-compound (2) were isolated from the roots of various South African species of the genera Athanasia and Pentzia. These acids are of interest as possible intermediates in the biosynthesis of polyacetylenes from crepenynic acid. The linoleyl ester of (1) was also identified. In his continuing study of South African members of the Compositae, Bohlmann identified a related pair of C18 compounds (3) and (4) from a number of species of Senecio. The two C18 compounds (1) and (2) have also been reported, occurring as their methyl esters in Athanasia tridens, along with the new C17 olefin derivative (5). Bohlman has suggested that (5) is biosynthesized by loss of carbon dioxide and water from the β-hydroxy C18 compound (6). Clibadium cf. glomeratum has also yielded a new C17 compound (7). Further C17 compounds are related to dehydrofalcarinone; (8) and (9) were identified in various South African species of Nidorella, while the South American Diotis maritima yielded the dihydro-derivative (10), related to (8). One new C16 compound has been identified. The aldehyde (11) was found in Siegesbekia jorullensis.

A number of C13 and C14 compounds have also been reported from various members of the Compositae. Bohlmann identified four new thiophen derivatives (12)–(15) from Cullumia setosa, along with other known thiophens. A polyacetylene has been isolated for the first time from Brickellia laciniata. This is a new C14 compound, with a novel pattern of unsaturation (16), and it occurs as a mixture of stereoisomers. The stereochemistry has not yet been determined. A study of compounds that are capable of stimulating the germination of safflower rust (Puccinia carthami) and which are produced by germinating safflower (Carthamus tinctorius) revealed a number of polyacetylenic hydrocarbons. A number of these are C13 compounds that are new to this well-studied species, and (17)–(19) are new compounds. A careful re-examination of the polar fraction of the aerial parts of Centaurea ruthenica revealed over twenty new compounds. Most of these are C13 compounds, along with some C10 and C14 compounds, all of them present in trace amounts. Complete separation of the components was not always possible, but the structures (20)–(48) were unravelled from spectroscopic evidence. The new compounds help to extend the biosynthetic schemes for these compounds.

Bohlmann has also discovered a number of C12 compounds among members of the family Compositae. The sulphur-containing compound (49) occurs in Chrysanthemum coronarium, along with a number of known, related cornpounds. Emilia coccinea and E. sagittata afforded a number of C12 compounds (50)–(54), which are suggested as the biosynthetic precursors of the better known C11 compounds. Two representatives (55) and (56) of a new type of chloro-aromatic thiophen compound occur in Helichrysum tenuifolium and H. panduratum, along with the related, non-aromatized compound (57). A chloro-enol ether (58) has been proposed as the biosynthetic precursor of these compounds, as shown in Scheme 1.

A number of C11 acetylenes (59)–(67) occur in Cineraria species, and the chemotaxonomy of the genus Cineraria is discussed by Bohlmann with reference to these and related compounds. Several sources of new C10 compounds have been found. These compounds are derivatives of matricaria ester, with which they often co-occur. The lactme (68) was isolated from Solidago altissima, and the seasonal variation of its concentration and those of matricaria ester and dehydromatricaria ester was observed. Chrysothamnus parryi gave four new derivatives of matricaria ester, i.e. (69)–(75). A number of known compounds were isolated from Artemisia absinthium, along with a new thiophen derivative of dehydromatricaria ester (76). Two C10 furano-acetylenes (77) and (78) were identified in Felicia filifolia.

A number of compounds were isolated from the roots of Pituranthus tortuosus (Umbelliferae), and three of these are new compounds. The structures of (79) and (80) were determined by spectroscopic and chemical-modification methods. A third compound was not fully characterized, but was shown to contain the part structure (81).

The fungus Peniophora resinosa yielded the new compound (82) in its (+)-form, along with related known compounds. Cultures of the fungus Polyporus anthracophilus produced a number of C10 polyacetylenes, among which one new isomer (83) was detected. An interesting collection of long-chain polyacetylenic and acetylenic compounds has been reported from a sponge of the genus Siphonchalina. These compounds, (84)–(89), are marine natural products, but sufficiently similar to some non-marine compounds to be mentioned here. Unlike the compounds found in Reniera fulva, (88) and (89) only contain terminal hydroxyl groups, leaving unresolved the problem of chirality raised in the previous review.

Other Acetylenic Compounds. – Six long-chain monoacetylenic compounds (90)–(95) have been found in the Amazonian Laurel, Licaria mahuba. The stereochemistry of the γ-lactone was determined by spectroscopic (mainly 1H n.m.r.)...