(2E,9E)-Pyronaamidine 9-(N-Methylimine), a New Imidazole Alkaloid from the Northern Mariana Islands Sponge Leucetta sp. cf. chagosensis

A new imidazole alkaloid, (2E,9E)-pyronaamidine 9-(N-methylimine) (4), was isolated along with the known compounds pyronaamidine (3) and kealiiquinone (5) from the yellow sponge Leucetta sp. cf. chagosensis collected near the Island of Rota, Northern Mariana Islands. Single-crystal X-ray diffraction analysis allowed the unambiguous assignment of the structure of compound 4, including the position of the exchangeable proton and the geometry of the two imino double bonds. Compound 4 exhibited mild cytotoxicity toward the A-549, MCF-7, and HT-29 human tumor cell lines.