Cytotoxic Sesquiterpene Lactones from Vernonia pachyclada from the Madagascar Rainforest

Bioassay-guided fractionation of the cytotoxic leaf extract of Vernonia pachyclada Baker led to the isolation of three new sesquiterpene lactones, designated glaucolides K−M (13). The structures of the new compounds were determined using 1D and 2D NMR spectroscopy, and the structure and stereochemistry of 1 were confirmed by single-crystal X-ray diffraction. Compound 3 showed moderate activity in the A2780 human ovarian cancer cell line, with an IC50 of 3.3 μM.