Secondary metabolites from the marine gastropod molluscs of Antarctica, southern Africa and South America.

Despite their perceived inaccessibility, the marine intertidal and benthic environments of Antarctica, southern Africa and South America have continued to provide marine natural products for chemists with unique opportunities to study the secondary metabolite constituents and chemical ecology of a diverse array of marine gastropod molluscs. This review covers the literature up to 31 January 2005 and describes the structures and, where applicable, biological activities of 100 secondary metabolites isolated from 21 species of marine gastropod molluscs. Not unexpectedly, the chemistry of chemically defended shell-less opisthobranchs dominates the natural product studies of molluscs collected from these regions of the southern hemisphere.

Sequestered chemistry of the Arminacean nudibranch Leminda millecra in Algoa Bay, South Africa.

Extracts of the endemic nudibranch Leminda millecra collected in Algoa Bay, South Africa, yielded four known metabolites, millecrones A (1) and B (2), isofuranodiene (5), and (+)-8-hydroxycalamenene (9), and nine new compounds, algoafuran (7), cubebenone (8), and a series of seven triprenylquinones and hydroquinones (21-27). A subsequent GC-MS survey of extracts of 21 of L. millecra's possible octocoral prey species in Algoa Bay identified the soft coral Alcyonium fauri as the source of 1 and the gorgonian Leptogorgia palma as the species producing 2 and 8.

Stolonic acids A and B, new cytotoxic cyclic peroxides from an Indian Ocean ascidian Stolonica species.

Two new 3,6-epidioxy-7,10-tetrahydrofurano C(26) unsaturated fatty acids, stolonic acids A (1) and B (2), were isolated from a previously undescribed ascidian species, Stolonica sp. collected off the Maldive Islands in the Indian Ocean. The structures and relative stereochemistry of 1 and 2 were determined using conventional spectroscopic methods. Both compounds exhibited antiproliferative activity against selected human melanoma and ovarian tumor cell lines, with IC(50) values of approximately 0.05-0.1 microg/mL.

Cembrane diterpenes from the southern African soft coral Cladiella kashmani.

Two known cembrane diterpenes, flaccidoxide (1) and (1Z,3E,7E,11S, 12S,14S)-11,12-epoxy cembra-1,3,7-trien-14-ol (2), and the new cembrane diterpene flaccidoxide-13-acetate (3) were isolated from specimens of Cladiella kashmani collected off Ponto do Oura, Mozambique. The modified Mosher's method established the previously unassigned absolute configuration of 1 as (1Z,3E,7E,11S,12S,13S, 14R)-14-acetoxy-11,12-epoxy cembra-1,3,7-trien-13-ol. Acetylation of 1 yielded 3 and thus confirmed the structure of 3 as (1Z,3E,7E,11S, 12R,13S,14R)-13,14-diacetoxy-11,12-epoxy cembra-1,3,7-triene. All three diterpenes were toxic to the brine shrimp Artemia salina.

A new furanosesterterpene from the South African nudibranch Hypselodoris capensis and a dictyoceratida sponge.

The known cytotoxic, linear beta-substituted sesterterpenes (18R)-variabilin (1) and 22-deoxyvariabilin (4) and a new variant, 22-deoxy-23-hydroxymethylvariabilin (5), were isolated from the endemic South African nudibranch Hypselodoris capensis together with the known ichthyotoxic sesquiterpenes nakafuran-8 (2) and -9 (3). One of H. capensis' dietary sponges, a Fasciospongia sp. collected simultaneously with the nudibranchs, yielded sesterterpenes 1, 4, and 5 and the ubiquitous prenylated furan derivative, furospinosulin-1 (7).

New diterpenes from the South African soft coral Eleutherobia aurea.

The known diterpenoids zahavin A and 9-deacetoxy-14,15-deepoxyxeniculin and the two new diterpenoids 7,8-epoxyzahavin A and xeniolide C were isolated from specimens of Eleutherobia aurea collected from Aliwal Shoal off the southern Kwazulu-Natal coast, South Africa. Standard spectroscopic methods were used for the structure determinations. The former three diterpenoids inhibit superoxide production in rabbit-cell neutrophils.

Chemical defense of common antarctic shallow-water nudibranchTritoniella belli eliot (Mollusca: Tritonidae) and its prey,Clavularia frankliniana rouel (Cnidaria: Octocorallia).

Extracts of the dorid nudibranchTritoniella belli and stoloniferan coralClavularia frankliniana were chromatographed and analyzed by(1)H NMR and thin-layer chromatography. Three glycerol ethers were detected inT. belli, primarily 1-O-hexadecyl glycerol (chimyl alcohol). Chimyl alcohol was also detected after gradient flash chromatography and reverse-phase HPLC purification in the tissues ofC. frankliniana. The common omnivorous predatory Antarctic sea starOdontaster validus, a likely predator of benthic invertebrates, showed feeding deterrence to small cubes ofT. belli mantle tissue placed on the tube feet along the ambulacral feeding groove, while always extruding the cardiac stomach when presented with cubes of shrimp tissue of similar size. Filter-paper disks soaked in an aqueous shrimp solution and then dried were found to elicit a broad range of feeding behaviors inO. validus, including movement of the shrimp disk to the mouth, extrusion of the cardiac stomach, and the assumption of a humped feeding posture. Chimyl alcohol-treated shrimp disks caused significant feeding deterrence in sea stars when compared with control disks (solvent plus shrimp treated disks alone).T. belli andC. frankliniana appear to employ a defensive compound that has been found in a variety of temperate and tropical mollusks, where it has been demonstrated to deter fish predators. We provide evidence for further deterrent capabilities of chimyl alcohol and of its trophic relationship in the polar ecosystem of McMurdo Sound, Antarctica.