The Synthesis, Structure, and Anticancer Activity of cis- and trans-4‘,7-Dihydroxyisoflavan-4-ols

cis -4‘,7-Dihydroxyisoflavan-4-ol ( 4 ) and trans -4‘,7-dihydroxyisoflavan-4-ol ( 5 ), two proposed metabolites of daidzein (4‘,7-dihydroxyisoflavone), have been synthesized and fully characterized for the first time. The vicinal coupling constants of the pyran ring protons are compatible with a half-chair conformation. The cis isomer is anancomeric while the trans isomer consists of a 68:32 mixture of two ring inversion conformers. Molecular mechanical calculations are in agreement with the half-chair conformation of the pyran ring and suggest that the cis isomer is biased because of an unfavorable gauche interaction of the equatorial hydroxyl and the axial phenyl group. The isoflavanols 4 and 5 are comparable to genistein (4‘,5,7-trihydroxyisoflavone) in antitumor activity against human prostate cancer cells.