Bromopyrrole alkaloids from a marine sponge Agelas sp.

Five new bromopyrrole alkaloids, 2-bromokeramadine (1), 2-bromo-9,10-dihydrokeramadine (2), tauroacidins C (3) and D (4), and mukanadin G (5), were isolated from an Okinawan marine sponge Agelas sp. The structures of 1-5 were elucidated on the basis of spectroscopic data and conformational analysis. Mukanadin G (5) has a tricyclic skeleton consisting of a fused tetrahydrobenzaminoimidazole and 2,5-dioxopyrrolidine moieties. Antimicrobial activities of 1-3, and 5 as well as three related known bromopyrrole alkaloids, keramadine (6), tauroacidin A (7), and taurodispacamide A (8) were evaluated.