Structures required of flavonoids for inhibiting digestive enzymes

The natural flavonoids as human digestive enzymes, such as α-glucosidase, α-amylase and aldose reductases inhibitors, have attracted great interest among researchers. The objective of this review is to overview the structures required of flavonoids for inhibiting these digestive enzymes. The hydroxylation on rings A and B of flavonoids improved the inhibition against these digestive enzymes. The hydroxylation on A-ring of flavones and isoflavones, especially at C-5 and C-7, significantly enhanced the inhibitory activities against digestive enzymes and the hydroxylation on positions C-3' and C-4' of B-ring of flavonoids remarkably improved the inhibition. The hydrogenation of the C2=C3 double bond on flavonoids decreased the inhibitory effects. The glycosylation of hyroxyl group on flavonoids weakened the inhibition against α-amylases and α-glucosidases. The glycosylation on 7-OH and 4'-OH of flavonoids significantly decreased the inhibition for aldose reductases. The glycosylation on 3-OH of flavonoids significantly increased or little affected the inhibition on aldose reductases. The methylation and methoxylation of flavonoids obviously weakened the inhibitory effects against α-amylase. The methylation and methoxylation of the hydroxyl group at C-3, C-3' and C-4' of flavonoids decreased or little affected the inhibitory potency against aldose reductases. And, the methylation and methoxylation of the hydroxyl groups at 5, 6, and 8 significantly increased the inhibitory capacity for aldose reductases. The methylation and methoxylation of flavonoids obviously affected the inhibitory effect for α-glucosidase in vitro depending on the replaced site.