Isoflavone C-glycosides isolated from the root of kudzu (Pueraria lobata) and their estrogenic activities

The chemical structures of six isoflavones (1–6) isolated from the kudzu root (Pueraria lobata) were elucidated on the basis of the NMR and MS analyses to be four isoflavone C-glycosides as 6″-O-α-d-glucopyranosylpuerarin (1), puerarin (2), 3′-methoxypuerarin (3), 6″-O-α-d-apiofranosylpuerarin (4), and two aglycons as biochanin A (5) and formononetin (6), respectively. The estrogenic activities of isolated compounds and related isoflavones were evaluated using a yeast two-hybrid assay. Genistein exhibited the highest activity among the evaluated compounds at 10−6 M followed by daidzein (10−5 M), baiochanin A (5) (10−5 M), daidzin (10−5 M), 3′,4′,7-trihydroxyisoflavone (10−3 M), and formononetin (6) (10−2 M). The isoflavone C-glycosides (1–4) and 4′,7-dimethoxyisoflavone showed no activities. In these results, it was found that the addition of 8-C-glucose or 3′-hydroxyl group to daidzein skeleton, or the substitution of hydroxyl functions to methoxyl groups, decreased the estrogenic activity of daidzein, on the other hand, the addition of 7-O-glucose moiety had no influence on the activity.