| The occurrence of secondary metabolites in several families of marine pulmonate molluscs was investigated with a focus on the origin and function of the natural products. The maurapyrones A-D and maurenone, isolated from the Costa Rican species Siphonaria maura, exhibited mild antimicrobial activity against the marine bacterium Vibrio anguillarum. Another population of S. maura from Puerto Vallarta, Mexico, was found to contain the vallartanones A and B. Both vallartanones A and B inhibited feeding by the fish Thallasoma lunare. S. thersites from Washington contained the known polypropionate pectinatone and two new homofuranones. Pectinatone is known to be antimicrobial against the bacterium Bacillus subtilis and against the human pathogen Staphylococcus aureus. It was also found to inhibit cell division and to be larvicidal, as were the homofuranones. Four new polypropionates and one known compound, siphonarin A, were isolated from an Australian species, S. baconi.; Two species of the family Trimusculidae were investigated were found to contain terpenoid metabolites. Both Trimusculus reticulatus from the California coast and T. conica from New Zealand contain high concentrations of secondary metabolites in the foot, mantle and mucus. The compounds were found to be larvicidal to Phragmatopoma californica at natural concentrations and the presence of the limpet or its mucus is also larvicidal. Three species of the family Onchidacea were found to contain onchidal, a known sesquiterpene acetate. These include Onchidella borealis, from Northern California, an Australian species, O. patelloides and a New Zealand species, O. nigricans. Onchidal inhibits the growth of Staphylococcus aureus and irreversibly binds to acetylcholinesterase.; To investigate the origin of polypropionate metabolites in siphonariids, labelling experiments were carried out by injecting {dollar}sp{lcub}14{rcub}{dollar}C labelled acetate of propionate into Siphonaria denticulata and S. virgulata, two Australian species. The limpets were found to incorporate propionate but not acetate into the purified polypropionate metabolites. Degradation studies demonstrated that the propionate precursor is not broken down before utilization in the biosynthesis of polypropionate metabolites. This is the first demonstration that polypropionate secondary metabolites are not dietary in origin, but are biosynthesized by the siphonariid pulmonate limpets. |
