Syntheses of Isoflavones and Isoflavone Glycosides, and Their Inhibitory Activity against Bovine Liver β-Galactosidase.

To clarify the relationship between the structure and inhibitory action toward β-D-galactosidase (EC 3.2.1.21) of isoflavones and isoflavone glycosides, a number of polyhydroxyisoflavones, and the α-L-rhamnosides and β-L-quinovosides of daidzein and genistein were synthesized. Among the polyhydroxyisoflavones, 2',3',4',7-tetrahydroxyisoflavone showed the strongest inhibitory activity (Ki = 26 × 10(-6) M). Among the glycosides, all the L-rhamnosides were strong inhibitors, of which genistein 4',7-di-O-α-L-rhamnoside was the strongest (Ki = 4.44 × 10(-6) M), while all the isoflavone β-L-quinovosides were considerably weak or possessed no inhibition.