POLYCYCLIC GUANIDINE-CONTAINING COMPOUNDS FROM THE MEDITERRANEAN SPONGE CRAMBE-CRAMBE - THE STRUCTURE OF 13,14,15-ISOCRAMBESCIDIN 800 AND THE ABSOLUTE STEREOCHEMISTRY OF THE PENTACYCLIC GUANIDINE MOIETIES OF THE CRAMBESCIDINS

The absolute stereochemistry of the pentacyclic guanidine moieties of crambescidin 816 (1)1 and of 13,14,15-isocrambescidin 800 (4), a new member of this family, was determined, based on chiral GC analysis of a derivative of 2-hydroxybutanoic acid, an ozonolysis product of the crambescidins. Significantly less antiviral activity and cytotoxicity were observed for 4.