Structural requirements of flavonoids for inhibition of protein glycation and radical scavenging activities

To clarify the structural requirements of flavonoids for formation of advanced glycation end-products (AGEs), various flavonoids were examined. The results suggested the following structural requirements of flavonoids for the inhibition of AGEs formation: (1) as the hydroxyl groups at the 3′-, 4′-, 5-, and 7-positions increased in number, the inhibitory activities became stronger; (2) the activities of flavones were stronger than those of corresponding flavonols, flavanones, and isoflavones; (3) methylation or glucosylation of the 4′-hydroxyl group of flavones, flavonols, and flavanones reduced activity; (4) methylation or glycosylation of the 3-hydroxyl group of flavonols tended to increase activity; (5) glycosylation of the 7-hydroxyl group of flavones and isoflavones reduced activity. In addition, various flavonoids with strong AGEs formation inhibitory activity tended to exhibit strong scavenging activity for 1,1-diphenyl-2-picrylhydrazyl and superoxide anion radicals, with several exceptions.