Estrogenic activity of constituents from the rhizomes of Rheum undulatum Linné.

Stilbenes have been reported to be phytoestrogen compounds owing to its structural similarity to the estrogenic agent diethylstilbestrol. To find new stilbene-derivative phytoestrogens, isolation of stilbene-rich R. undulatum was performed and led to identify six new compounds (1-5 and 28), one newly determined absolute configurations compound (27) together with 21 previously reported compounds (6-26). The structures of compounds were determined on the basis of extensive spectroscopic methods including 1D and 2D NMR and CD spectra data. All the isolated compounds were tested for their estrogenic activities in HepG2 cells transiently transfected with ERα, ERβ and ERE-reporter plasmid. Among them, stilbene-derivatives, piceatannol 3'-O-β-d-xylopyranoside (12), cis-rhaponticin (16) and rhapontigenin 3'-O-β-d-glucopyranoside (17), showed the more potent binding affinity for estrogen receptors than 17β-estrodiol.