Ascidians have developed multiple defensive strategies mostly related to physical, nutritional or chemical properties of the tunic. One of such is chemical defense based on secondary metabolites. We analyzed a series of colonial Antarctic ascidians from deep-water collections belonging to the genera Aplidium and Synoicum to evaluate the incidence of organic deterrents and their variability. The ether fractions from 15 samples including specimens of the species A. falklandicum, A. fuegiense, A. meridianum, A. millari and S. adareanum were subjected to feeding assays towards two relevant sympatric predators: the starfish Odontaster validus, and the amphipod Cheirimedon femoratus. All samples revealed repellency. Nonetheless, some colonies concentrated defensive chemicals in internal body-regions rather than in the tunic. Four ascidian-derived meroterpenoids, rossinones B and the three derivatives 2,3-epoxy-rossinone B, 3-epi-rossinone B, 5,6-epoxy-rossinone B, and the indole alkaloids meridianins A–G, along with other minoritary meridianin compounds were isolated from several samples. Some purified metabolites were tested in feeding assays exhibiting potent unpalatabilities, thus revealing their role in predation avoidance. Ascidian extracts and purified compound-fractions were further assessed in antibacterial tests against a marine Antarctic bacterium. Only the meridianins showed inhibition activity, demonstrating a multifunctional defensive role. According to their occurrence in nature and within our colonial specimens, the possible origin of both types of metabolites is discussed.

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New bengazoles 3-9 as inseparable mixtures are reported from the sponge Jaspis cf. coricea collected in Papua New Guinea. These compounds contain a new variation of the unusual bisoxazole core present in bengazole A [1]. The B-ring oxazole hexatetraol side chain is varyingly substituted with either myristic acid or 13-methylmyristic acid. Hydrolysis of three different bengazole mixtures each yielded an identical tetraol, bengazole Z [11].

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The Indonesian gorgonian Briareum sp. has afforded two new briarane stecholide diterpenes: 2,9-diacetyl-2-debutyrylstecholide H (1) and 13-dehydroxystecholide J (2), the semisynthetic 2beta-acetoxy-2-(debutyryloxy)stecholide E acetate (3), which was isolated as a natural product for the first time, along with the known compounds stecholides I-M (4-8), stecholide A acetate (9), and stecholide C acetate (10). The structures of the new compounds were deduced by extensive NMR studies (1H, 13C, 1H-1H COSY, NOESY, HMQC, and HMBC) and FABMS data (HR and LR). Cytotoxic activity was found for the first time in stecholide L (7).