Dihydrotubastrines: phenethylguanidine analogues from the Indo-Pacific marine sponge Petrosia cf. contignata.

Two phenethylguanidine derivatives, 7,8-dihydrotubastrine (1) and 4-deoxy-7,8-dihydrotubastrine (2), along with the sterol xestobergsterol A (3), were isolated from the marine sponge Petrosia cf. contignata. The structures of the new natural products 1 and 2 were based on spectroscopic data and comparison to the literature properties for semisynthetic 1. This is the first example from this compound class with a saturated acyclic C2 unit.