Ebenfurans IV−VIII from Onobrychis ebenoides: Evidence that C-Prenylation is the Key Determinant of the Cytotoxicity of 3-Formyl-2-arylbenzofurans

Phytochemical investigation of a methanol extract of Onobrychis ebenoides yielded five new 3-formyl-2-arylbenzofurans, namely, ebenfurans IV-VIII (1-5), together with the known compounds ebenfurans I, II (6), and III (7). Only 1 and 7 exhibited growth inhibitory activity against MCF-7 and Ishikawa cells, suggesting that the prenyl moiety at position C-5 is the key determinant of the cytotoxic activity of this group of compounds.