Novel secondary metabolites from selected marine invertebrates

Chemical studies of a Northeastern Pacific tunicate and three Papua New Guinea sponges have led to the isolation of sixteen new secondary metabolites. The structures of the new compounds were determined by spectroscopic analysis and chemical interconversions. The absolute stereochemistry of imbricatine, a previously reported starfish metabolite, has also been determined. The northeastern Pacific tunicate Ritterella rubra has been found to contain a novel series of aromatic butenolides, rubrolides A-H (149-156). The structures of the rubrolides were solved by the analysis of NMR (¹H, ¹³C, COSY, nOe, HETCOR, FLOCK, HMQC and HMBC), MS and IR data combined with chemical interconversions. FLOCK, a new ¹H/¹³C long-range correlation experiment, played a key role in establishing the rubrolide carbon skeleton. The rubrolides represent the largest family of non-nitrogenous tunicate metabolites. The protein phosphatase inhibitory activity and the potent antibiotic activities of the rubrolides warrant further investigation. The absolute stereochemistry of imbricatine (179), a compound reported from the starfish Dermasterias imbricata, has been determined by comparing the optical properties of its chemical degradation products with those of model compounds. Raney nickel reduction of 179 yielded benzyltetrahydroisoquinoline 188a which was methylated to give 188b. Comparison between the CD spectrum of 188b and those of model compounds 189 and 190 solved the absolute stereochemistry of the tetrahydroisoquinoline fragment of 179. Reductive hydrolysis of 179 followed by oxidation yielded histidine disulphide 182. Comparison of the optical rotation of 182 with the reported value solved the absolute stereochemistry of the histidine fragment of 179. Attempts to study the biogenesis of 179 were unsuccessful. Examination of three Papua New Guinea sponges resulted in the isolation of eight new compounds. Six new bastadins (211-216) were isolated from Ianthella basta. The structures were elucidated by spectroscopic analysis as well as comparison with the previously reported bastadins. A Xestospongia species was found to contain xestospongin E (238), a new metabolite, and a number of known xestospongins. Both the bastadins and the xestospongins possess antibiotic and cytotoxic activities. A symmetrical enyne, callydiyne (247), was isolated from Callyspongia flammea. The structure of 247 was determined by spectroscopic studies.Science, Faculty ofChemistry, Department ofGraduat