New and biologically active imidazole alkaloids from two sponges of the genus Leucetta

Chemical investigation of two sponges, Leucetta chagosensis and Leucetta cf chagosensis, collected from the Great Barrier Reef and the Fiji Islands, respectively, has led to the isolation of three new imidazole alkaloids (1−3), along with the known compounds isonaamine B (4) and naamine A (5). The structures of the new compounds (1−3) were elucidated by employing spectroscopic techniques (NMR, MS, UV, and IR). The structures of the known compounds 4 and 5 were determined by comparison of their 1H and 13C NMR spectroscopic data with published values. Compounds 1 and 2 were found to be cytotoxic toward several tumor cell lines (GI50 values ranged from 1.3 to 7.0 μg/mL).