Antibacterial and anticholinesterase activities of aplysamine-4, a bromotyrosine-derived metabolite of a Red Sea marine sponge.

Aplysamine-4, a metabolite of likely bromotyrosine biogenesis, was isolated from an unidentified verongid sponge from the Red Sea. The compound was identified by heteronuclear magnetic resonance experiments, and by electrospray ionization tandem mass spectrometry. The compound exhibited moderate inhibitory activity on several Gram positive and Gram negative bacteria, and was also found to be a non-competitive reversible inhibitor of acetylcholinesterase. At pH 7.4, a Ki value of 16 and 2 microM was determined with electric eel and insect recombinant acetylcholinesterase, respectively. A deprotonated form of aplysamine-4 was obtained by alkaline treatment of the natural compound and it was shown to be less active than the protonated form.