Plexauddae flourish as they do nowhere in the world. Gorgonian corals (order Gorgonacea, phylum Cnidaria) are 4571 4572 A.D. RODRIGUEZ conspicuous members of most tropical and subtropical marine habitats, being the most abundant octocorals found in the West Indies. With over 195 species documented from these two major families, gorgonian octocorals represent an estimated 38% of the known fauna, l Studies of the natural products chemistry of this interesting group of marine invertebrates began in the late 1950's. Since these early investigations, numerous studies of the chemistry of gorgonian corals have been published and summarized. 2-9 This Report documents the exciting chemistry that has been generated through the investigation of gorgonian octocorals from the West Indian region. It includes only research published in refereed journals up to December, 1994. A short communication in Science by Burkholder and Burkholder in 1958, highlighting the occurrence of antibiotic substances in gorgonian corals from Puerto Rico, was used as the starting point for the present review, to This Report is not intended to be comprehensive but instead concentrates on novel marine natural products with interesting biological and pharmaceutical properties. With the exception of several unusual sterols having interesting functionalities, marine sterols, carotenoids, fatty acids, and biopolymers isolated have not been included, since they have been reviewed by specialists, l 1-15 Studies of the chemical ecology aiming at the elucidation of the defensive roles of secondary metabolites from West Indian gorgonians and the value of secondary metabolite composition as a chemotaxonomic tool are discussed. The cited articles were retrieved from computer literature searches by use of Chemical Abstracts (CA Selects), MarinLit, STN International and also NAPRALERT. Terms such as West Indian, Caribbean, gorgonian, sea whip, octocoral, and phylla names were used. The primary focus will be the structural chemistry and biological activities of the metabolites produced by a relatively small group of gorgonians found within a limited geographic area. Wherever possible, every effort was made to record the biological and pharmacological properties of new metabolites. Since marine natural products in general are often the targets of synthetic chemists, we include synthetic work, where available, on novel compounds isolated from these animals. We hope to illustrate the diversity of compounds produced by West Indian gorgonians, while highlighting their specialized ability to biosynthesize secondary metabolites with promising pharmacological activity. 16-19 Gorgonian metabolites possess novel structures that are largely unknown from terrestrial sources. These animals are now recognized to produce acetogenins, sesquiterpenoids, diterpenoids, prostanoids, and, in some cases, highly functionalized steroids. 7 The chemistry of West Indian gorgonian octocorals will be presented taxonomically according to genus and species (in alphabetical order) rather than by chemical class, although in some cases a given compound could be assigned equally well to different categories. This categorization was selected not only for its convenience but also because it reveals an interesting fact: so far only a small percentage of the many species of gorgonians from this region (less than 20%) appears to have been systematically scrutinized for their secondary metabolite content; and many species await chemical investigation. The phylogenetic position of the genus Briareum, which appears to be identical with the Pacific species Solenopodium, has long been the subject of debate, l Two documented species are known. One of them, Briareum asbestinum, is an exceedingly variable species commonly distributed from southern Florida through most of the West Indies. The second, Briareum polyamhes, is a recently discovered species that forms encrustations on rocks, Natural products of gorgonian octocorals 4573 dead coral, and other living gorgonians. These animals are particularly rich in asbestinane and briarane diterpenoids. (Common Briareum, corky sea fingers) Studies of the chemistry of this interesting species began in the early 1960's with the discovery of a carbonyl-containing crystalline solid (later to be known as Briarein A) and the occurrence of taurobetaine in specimens collected near South Bimini (The Bahamas). 20-22 No appreciable amount of sesquiterpenes appears to have been found in this species. Briareum asbestinum elaborates diterpenes possessing the asbestinin and briarein ring systems. The asbestinins are a group of irregular diterpenoids that are related to the eunicellin-cladiellin group by 1,2-migration of the methyl group on the six-membered rings. Asbestinins 1-5 (1-5) were isolated from a sample of B. asbestinum collected in Belize, 23 whereas asbestinins -2, -3, -4, and -5 together with the derivatives asbestinin-5 acetate (7) and asbestinin epoxide (8) were obtained from samples collected in Honduras. 24 The structure of asbestinin-1 (1) was determined by single-crystal X-ray diffraction on the corresponding diol 6 and the structures of asbestinins 2-5 (2-5) were assigned from spectral analysis and chemical interconversions. 23 Structures for 7 and 8 were likewise derived from spectroscopic arguments and confirmed by chemical interconversions. 24 Several of the asbestinin derivatives show pharmacological activity. Compounds 1, 5, and 6 have the ability to antagonize the effects of acetylcholine on guinea pig ileum preparations. Compounds 5 and 6 also exhibit histamine antagonism in this same assay. 24 10 R=Ac 1 2 R=Ac
Output: TETRAHEDRON REPORT NUMBER 370 THE NATURAL PRODUCTS CHEMISTRY OF WEST INDIAN GORGONIAN OCTOCORALS