| Research Abstract |
Due to their unusual living environment as compared with terrestrial organisms, marine organisms, such as marine sponge and octocoral, metabolite and produce a variety of substances which often have various unprecedented chemical structures and exhibit significant biological activities. In search of new pharmaceutically valuable substances from marine organisms, we have investigated the chemical constituents of marine sponges mostly inhabiting the Okinawan coral reefs.
We collected marine sponges at Kerama and Yaeyama Islands, Okinawa prefecture, in July 1991 and 1992. The lipid-soluble and water-soluble portions of these marine sponges were subjected to bioassay-guided separation, such as brine-shrimp toxicity, antifungal and cytotoxic activities. So far, we have elucidated the chemical constituents of following marine sponges.
1. Two new 3-keto-4-methylene steroids named theonellasterone and conicasterone were isolated from the marine sponge Theonella swinhoei and elucidated their absolute stereostructures. We also isolated a new dimeric steroid named bistheonellasterone together with two known 4- methylene sterols. Bistheonellasterone is a dimeric steroid biosynthesized regio- and stereospecifically by presumable intermolecular Diels-Alder cycloaddition of theonellasterone.
2. The examinations of cytotoxicity against L1210 and KB cells led to the isolation of five sesterterpenes, heteronemin, manoalide, secomanoalide, (E)-neomanoalide, and (Z) -neomanoalide, as active principles produced by the marine sponge Hyrtios erecta. Manoalide was obtained as a (ca. 1:1) mixture of 25-epimers. We have examined to reconfirm the 4R absolute configuration of these manoalide family.
3. Two new antibiotic polyacetylenes were isolated from an marine sponge Adocia sp. and their absolute stereostructures were elucidated on the basis of chemical and physicochemical evidence.
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