Antiproliferative compounds of Helmiopsis sphaerocarpa from the Madagascar rainforest.

Bioassay-directed separation of an ethanol extract of the leaves of Helmiopsis sphaerocarpa L.C. Barnett (Sterculiaceae) led to the isolation of the new compound 14alpha,15alpha-epoxy-3beta-hydroxytaraxerane (1) and the four known compounds taraxerol (2), stigmast-5-en-3-ol (3), 5alpha,8alpha-epidioxy-24(S)-methylcholesta-6,22-dien-3beta-ol (4), and 24xi-hydroperoxy-24-ethylcholesta-4,28(29)-dien-3-one (5). The structure of the new compound 1 was established on the basis of interpretation of its 1D and 2D NMR spectroscopic data. All the compounds were tested against A2780 human ovarian cancer cell lines, and compounds 4 and 5 showed mild antiproliferative activity, with IC(50) values of 16 and 7 microg mL(-1), respectively.