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

Abstract 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.