Cytotoxic isoprenylated flavonoids from the roots of Sophora flavescens

Three new flavonoids, which are isoprenylated by fused 2,2-dimethyl-3,4-dihydro-2H-pyran moieties, were isolated from the roots of Sophora flavescens and named flavenochromanes A-C (1-3). Their structures were elucidated by spectroscopic methods, including 2D-NMR techniques. Flavenochromane C (3) showed strong cytotoxic activity against A549 (lung carcinoma), 1A9 (ovarian carcinoma), KB (epidermoid carcinoma of the nasopharynx), and KB-Vin (drug-resistant variant KB) cell lines with IC50 values less than or equal to 1.7 muM, and significant activity against the MCF-7 (breast adenocarcinoma) cell line with an IC50 value of 3.6 muM. Flavenochromane B (2) displayed slightly lower inhibitory effects (IC50 3.2-6.9 muM) as compared with 3.