On the structures of crambescins B and C1.

Revised structures have been assigned to the cyclic guanidine-containing crambescins B [3] and C1 [5], from the Mediterranean sponge Crambe crambe. The revisions were based on the fabms/cid/ms spectra of the [M+H]+ ions from crambescins B and C1 and hrfabms measurements on key fragment ions in the ms/ms spectra, which identify losses of C9H19 and C8H18N3O side-chains.