Antiproliferative limonoids of a Malleastrum sp. from the Madagascar rainforest.

Bioassay-guided fractionation of an ethanol extract of a Malleastrum sp. afforded three new limonoids, malleastrones A-C (1-3), respectively. Each limonoid contained a rare tetranortriterpenoid skeleton. Structure elucidation of the isolates was carried out by analysis of one- and two-dimensional NMR and X-ray diffraction data. The novel isolates 1 and 2 were tested for antiproliferative activity against a panel of cancer cell lines and exhibited IC 50 values ranging from 0.19 to 0.63 pM.