POLYCYCLIC GUANIDINE ALKALOIDS FROM THE MARINE SPONGE CRAMBE-CRAMBE AND CA-816(+ CHANNEL BLOCKER ACTIVITY OF CRAMBESCIDIN)

Four pentacyclic guanidine derivatives (crambescidin 800 5!, crambesc idin 816 6!, isocrambescidin 800 9!, and crambidine 10!) related to ptilomycalin A 11! have been isolated from the Mediterranean sponge Crambe crambe. Isocrambescidin 800 and crambidine are new derivatives, the structures of which have been determined on the basis of their sp ectral properties. The absolute configuration of crambescidin 816 at t he stereogenic center C-43 has been determined by applying Mosher's me thod. Pharmacological and biological activities of the Crambe crambe a lkaloids are reported. In particular, crambescidin 816 was found to ha ve a potent Ca++ antagonist effect and to inhibit the acetylcholine-in duced contraction of guinea pig ileum at very low concentrations.