Revised structures have been assigned to the cyclic guanidine-containi
ng 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.