Structures and absolute stereochemistry of isocyanide and isothiocyanate amphilectenes from the Caribbean sponge Cribochalina sp.

Three new diterpenes (5-7), based on amphilectene skeleton, were isolated from the Caribbean sponge Cribochalina sp.. AII contain isocyanide and isothiocyanate functions and are epimers at C-7 of previously characterized diterpenoids. The structures of 5-7 were established by spectroscopic techniques. The sponge extract also showed the presence of the known metabolite 4, together with the new bicyclic diterpene 8, potential precursor of the co-occurring amphilectenes. For the first time, the absolute configuration of the amphilectene skeleton has been assigned by applying the modified Mosher's method on a derivative of the main compound 4. The isocyanide 4 reduced the proliferation of lymphocytes T and B under various stimuli.