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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. Compounds 1 and 2 were found to be cytotoxic toward several tumor cell lines (GI(50) values ranged from 1.3 to 7.0 microg/mL).

Geometricin A (1), together with the known compounds (7E,12E,18S,20Z)-variabilin (2), clathryimine A (3), tryptophol (4), and L-tryptophan, has been isolated from the methanol extract of the Australian sponge Luffariella geometrica. The structure of the new compound geometricin A (1) was elucidated by employing spectroscopic techniques (NMR, MS, UV, and IR) and by comparison of its NMR data with those of the calyculins and calyculinamides. Geometricin A (1) was found to be moderately cytotoxic toward the tumor cell lines HM02 and HEPG2 with GI50's of 1.7 and 2.8 microg/mL, respectively, and to have antialgal activity (growth inhibition zone 5 mm at the 50 microg level).