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 (1)H and (13)C NMR spectroscopic data with published values.

Leucamide A: a new cytotoxic heptapeptide from the Australian sponge Leucetta microraphis.

Leucamide A (1), a bioactive cyclic heptapeptide containing a unique mixed 4,2-bisheterocycle tandem pair consisting of a methyloxazole and thiazole subunit was isolated together with the known compound BRS1 (2), from the dichloromethane extract of the Australian marine sponge Leucetta microraphis. The planar structure of leucamide A (1) was elucidated by employing spectroscopic techniques (NMR, MS, UV, and IR). Its absolute stereochemistry was established by chemical degradation, derivatization, and chiral GC[bond]MS analysis.