This research project is directed toward the isolation and structural elucidation of antimicrobial compounds from marine organisms. Extracts of marine organisms are screened in the field to determine which organisms should be collected on a larger scale for study in the laboratory. The isolation of the antimicrobial compounds is accomplished using the antimicrobial assay to direct the chemical fractionation. The structural elucidations make use of all modern spectroscopic methods and, whenever possible, compounds are interrelated through chemical conversions. We propose to examine examples of chemical interactions between marine organisms since these often yield physiologically active compounds. We wish to expand the scope of our field assays to include an assay for inhibition of cell division in fertilizzed sea urchin eggs. During the present grant period we have determined the structures of more than fifty novel compounds, most of which have antimicrobial activity. We have described the first naturally-occurring carbonimidic dichlorides, a group of cyclic peroxides, a diterpene diisonitrile, and several other novel structural types. Over 20% of the organisms which we have screened showed antimicrobial activity, with some collections of tropical sponges comprising better than 50% active species. We will continue to isolate and identify active constituents from these marine organisms, concentrating on marine sponges from the Caribbean and tropical Pacific islands. Active compounds will be submitted for pharmaceutical evaluation. Potentially useful compounds may be synthesized if required for further studies.