Cembranoid Diterpenes Related to Sarcophytol A From the Soft Coral Sarcophyton trocheliophorum (Alcyonacea)

Abstract

An investigation of metabolites from the soft coral Sarcophyton trocheliophorum collected at North East Reef, Orpheus Island, has yielded three simple cembranoid diterpenes , namely (7R,8R,14S,1E,3E,11E)-7,8-epoxycembra-1,3,11-trien-14-ol (1), (7R,8R,14S,1E,3E,11E)-14-acetoxy-7,8-epoxycembra-1,3,11-triene (2) and (7R,14S,1E,3E,8E,11E)-cembra-1,3,8,11-tetraene-7,14-diol(3), together with the known dihydrofuran sarcophytoxide (4). The diterpenes (2) and (3) were previously reported as synthetic derivatives of sarcophytol A, but this is the first report of their natural occurrence. The three mildly cytotoxic diterpenes (1)-(3) are structural modifications of the antitumour promotor sarcophytol A (5). Structures were established by high-resolution n.m.r. spectroscopy and interconversion. The absolute stereochemistries of the metabolites were determined by use of the Mosher n.m.r. method, and the stereochemistry at C14 was shown to be the same as that of sarcophytol A in each case. These results are in agreement with the published absolute stereochemistries of the metabolites determined by the Horeau method. Full n.m.r. assignments for (11S,12S,14S,1E,3E,7E)-11,12-epoxycembra-1,3,7-trien-14-ol (6) and (11S,12S,14S,1E,3E,7E)-14-acetoxy-11,12-epoxycembra-1,3,7-triene (7) are given.