Stereochemical evaluation of sesquiterpene quinones from two sponges of the genus Dactylospongia and the implication for enantioselective processes in marine terpene biosynthesis

Silver nitrate flash chromatography of the organic extract from the sponge Dactylospongia elegans has led to the isolation of three new sesquiterpene quinones isohyatellaquinone (7), 7,8-dehydrocyclospongiaquinone-2 (8) and 9-epi-7,8-dehydrocyclospongiaquinone-2 (9) together with the known quinones dictyoceratidaquinone (6), mamanuthaquinone (10), ilimaquinone (11), hyatellaquinone (12) and the sesterterpene furospinosulin (22). The relative stereochemistry of dictyoceratidaquinone (6) is assigned on the basis of NOESY analysis. A second species of Dactylospongia, thought to be new to science, was found to contain ent-(7) together with the new quinone neomamanuthaquinone (13). The isolation of antipodal sesquiterpenes from closely related species has implications for the stereochemical evaluation of terpene metabolites. The biosynthetic processes in these marine sponges may involve terpene synthases that do not discriminate chiral substrates or may result from the presence of multiple terpene synthases, each with differing enantioselectivity.