Dichapetalins from Dichapetalum species and their cytotoxic properties

Six dichapetalins named dichapetalins N-S were isolated from Dichapetalum mombuttense, Dichapetalum zenkeri and Dichapetalum leucosia. They were accompanied in the same plants by the known dichapetalins A, B, C, I, L and M. The structures of the compounds were elucidated by 1D and 2D NMR experiments and mass spectrometry. They all possessed the dammarane skeleton substituted at position C-3 by a C6-C2 unit forming a 2-phenylpyran moiety. All contained a lactone ring in the side chain except dichapetalins O, Q and R, in which this ring was replaced by a lactol. Dichapetalin Q and R were also the first dichapetalins bearing a tertiary methyl and a double bond instead of the cyclopropane of the dammaranes. All these compounds were assayed against cancer cell lines HCT116 and WM 266-4 and displayed cytotoxic and anti-proliferative activities in the 10(-6) to 10(-8)M range.