During the course of studies in search of bioactive marine natural products, we have investigated the chemical constituents of two stolonifers: Clavularia viridis and C. koellikeri (Coelenterata, Anthozoa, Octocorallia, Stolonifera, Clavulariidae), which were collected in the coral reefs of Okinawa waters. This paper provides the evidence which substantiates their absolute stereostructures. 1) Anti-tumor active new prostanoids such as claviridenone-a (1),-b (2),-c (3),-d (4), and the 20-acetoxyl derivatives of 2 (5) and 3 (6) were isolated from C. viridis and their absolute stereostructures have been elucidated on the basis of chemical and physicochemical evidence including the application of the CD exciton chirality method. 2) A new trinorsesquiterpene named clavukerin A (32), which is a fairly unstable oil, was isolated from C. koellikeri and the absolute stereostructure has been determined by means of the chemical reactions, the CD analysis, and the X-ray crystallographic analysis of the diepoxide of clavukerin A (32).
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