Naturally Occurring Cytotoxic [3'→8″]-Biflavonoids from Podocarpus nakaii.

Bioassay-guided fractionation of the EtOH extract of the dried twigs of Podocarpus nakaii Hayata (Podocarpaceae), endemic plant in Taiwan has resulted in isolation of four [3'→8″]-biflavonoid derivatives, amenotoflavone (AF), podocarpusflavone-A (PF), II-4″,I-7-dimethoxyamentoflavone (DAF), and heveaflavone (HF). Their structures were determined by physical and extensive spectroscopic analyses such as (1)H, (13)C, (1)H-(1)H COSY, HMQC, and HMBC, as well as comparison with literature values. Compounds PF and DAF showed significant inhibitions against DLD, KB, MCF-7, HEp-2 tumor cell lines (ED50 ca. 4.56-16.24 μg/mL) and induced cell apoptosis in MCF-7 via mainly sub-G1/S phase arrest. Furthermore, these compounds exhibited moderate Topoisomerase I inhibitory activity.