Inhibition of Lipoxygenase and Peroxidase Reaction by Some Flavonols and Flavones: The Structure-Activity Relationship

Some flavonoids were investigated for their effects on lipoxygenase and peroxidase. The strongest inhibitor of lipoxygenase was kaempferol with one hydroxyl group situated at the 4' position in the B ring, with activity of 21.2 +/- 2.03 calculated per mu mole of compound. The weakest inhibition was observed for diosmetin with a hydroxyl group at the 3' position and a methoxyl group at 4' in the B ring, with activity of 1.17 +/- 0.77 per mu mole. Peroxidase was most strongly inhibited by quercetin (22.7 +/- 0.05) with two hydroxyl groups in the B ring at 3' and 4'. The weakest inhibitor of peroxidase was genkwanin (0 +/- 0.16) with one hydroxyl group at position 4' in the B ring and methoxyl at position 7 in the A ring. The correlation coefficient between reduction of Fe3+ by flavonoids and inhibition of lipoxygenase by these compounds was 0.72 and the reduction of Fe3+ and inhibition of peroxidase was 0.24. The results show that inhibition of peroxidase is weakly associated with reducing properties of phenols and inhibition of lipoxygenase may be associated with antioxidant properties of flavonoids.