Novel polycyclic guanidine alkaloids from two marine sponges of the genus Monanchora

Two marine sponges of the genus Monanchora (Poecilosclerida, Crambeidae) have been found to contain new polycyclic guanidine alkaloids bearing the (5,6,8b)-triazaperhydroacenaphthylene skeleton. Their structures have been determined by detailed spectroscopic analysis. Dehydrobatzelladine C (1) has been isolated from M. arbuscula and crambescidins 359 (2) and 431 (3) from M. unguiculata. The chemotaxonomic implications of these findings are discussed.