New Bromotyrosine Metabolites from the Sponge Aplysinella rhax

Four new bromotyrosine metabolites (3–6) along with the previously described compounds psammaplin A (1) and bisaprasin (2) have been isolated from the sponge Aplysinella rhax collected from Guam, Palau, and Pohnpei. Based upon the results of extensive spectroscopic analysis and chemical reaction, the structures of psammaplins A1 (3) and A2 (4) have been determined to be a N,N-dimethylguanidium salt of psammaplin A sulfate and its bis-N,N-dimethylguanidium disulfate derivative, respectively. Aplysinellin A (5) possesses an additional bromotyrosine-derived C9 unit connected directly to the carbon framework of psammaplin A by a biphenylic linkage while aplysinellin B (6) is the corresponding cyclic enol ether. These compounds exhibited moderate cytotoxicity and inhibitory activities against farnesyl protein transferase and leucine aminopeptidase.