Cytotoxic triterpenes from a marine sponge, Stelletta sp.

Bioassay-guided fractionation of an extract of a marine sponge, Stelletta sp., has led to the isolation and characterization of four new cytotoxic isomalabaricane triterpenes, named stellettins C (1), D (2), E (3), and F (4). Three known triterpenes (5-7) were also isolated from the same extract. The most sensitive of the tested cell lines (e.g., leukemia, central nervous system, renal) generally responded with GI50 concentrations in the low-to-mid nanomolar range.