Inhibition of α-glucosidase and α-amylase by flavonoids

The inhibitory activity of six groups of flavonoids against yeast and rat small intestinal alpha-glucosidases and porcine pancreatic alpha-amylase was compared. and chemical structures of flavonoids responsible for the inhibitory activity were evaluated. Yeast a-glucosidase was potently inhibited by the anthocyanidin. isoflavone and flavonol groups with the IC50 values less than 15 mu m. The following structures enhanced the inhibitory activity: the unsaturated C ring. 3-OH. 4-CO. the linkage of the B ring at the 3 position, and the hydroxyl substitution on the B ring. Rat small intestinal alpha-glucosidase was weakly inhibited by many flavonoids, and slightly by the anthocyanidin and isoflavone groups. 3-OH and the hydroxyl substitution oil the B ring increased the inhibitory activity. In porcine pancreatic alpha-amylase, luteolin, myricetin and quercetin were potent inhibitors with the IC50 values less than 500 mu M. The 23-double bond, 5-OH, the linkage of the B ring at the 3 position. and the hydroxyl substitution on the 13 ring enhanced the inhibitory activity, while 3-OH reduced it.