New cytotoxic bis 5-alkylresorcinol derivatives from the leaves of Oncostemon bojerianum from the Madagascar rainforest

Bioassay-directed fractionation of a CH2Cl2-MeOH extract of the leaves of Oncostemon bojerianum, resulted in the isolation of eight new 5-alkylresorcinols, named oncostemonols A-H (1-8), and two known derivatives, (8'Z)-1,3-dihydroxy-5-[16'-(3",5"-dihydroxyphenyl)-8'-hexadecen-1'-yl]benzene (9) and (8'Z)1,3-dihydroxy-5-[14'-(3",5"-dihydroxyphenyl)-8'-tetradecen-1'-yl]benzene (10). The structures of the new compounds 1-8 were elucidated on the basis of extensive 1D and 2D NMR spectroscopic interpretation and chemical derivatization. All the compounds exhibited cytotoxic activity against the A2780 ovarian cancer cell line.