Heteroaromatic alkaloids, nakijinamines, from a sponge Suberites sp.

The structures of seven new secondary metabolites isolated from an Okinawan marine sponge Suberites sp., nakijinamines A (1), B (2), and F-I (3-6) and 6-bromoconicamin (7), have been elucidated on the basis of spectroscopic analysis, chemical conversion, and conformational analysis. These analyses disclosed that 1-6 were heteroaromatic alkaloids having the hybrid structures of an aaptamine-type alkaloid and an indole alkaloid, while 7 was a bromoindole alkaloid. Nakijinamine I (6) is the first example of an aaptamine-type alkaloid possessing a 1,4-dioxane ring. Antimicrobial activities of 1-7 were evaluated.