CHEMICAL STUDIES OF EGYPTIAN OPISTHOBRANCHS - SPONGIAN DITERPENOIDS FROM GLOSSODORIS-ATROMARGINATA

Five new spongian diterpenoids 1-5 have been isolated from the mollusk Glossodoris atromarginata along with four known related metabolites ( 6-9). The structures were solved by extensive spectroscopic analysis a nd chemical correlation. The absolute stereochemistry of compound 2 wa s determined by Mosher's method. A dietary origin is inferred for all these molecules on the basis of their structural analogies with known sponge metabolites, but their transfer from the digestive glands to th e dorsal skin suggests a defensive role to thwart predation.