Flavonoids as peroxynitrite scavengers: the role of the hydroxyl groups.

Toxicol In Vitro 2001 Feb;15(1):3-6 Related Articles, Books, LinkOut Flavonoids as peroxynitrite scavengers: the role of the hydroxyl groups.Heijnen CG, Haenen GR, van Acker FA, van der Vijgh WJ, Bast A.Department of Pharmacology and Toxicology, Faculty of Medicine, Universiteit Maastricht, PO Box 616, 6200 MD Maastricht, The Netherlands. c.heijnen@farmaco.unimaas.nlIt has been reported that flavonoids efficiently protect against peroxynitrite toxicity. Two pharmacophores have been identified in flavonoids, namely the catechol group in ring B and the hydroxyl (OH) group at the 3-position. In this study, this structure-activity relationship was further examined. It was found that catechol (1,2-dihydroxybenzene) is a potent peroxynitrite scavenger, whereas phenol (hydroxybenzene) is not. Of the flavonols tested without a catechol group in ring B, kaempferol (OH groups at positions 3,5,7,4') and galangin (OH groups at positions 3,5,7) are also potent scavengers, whereas apigenin (OH groups at positions 5,7,4') and chrysin (OH groups at positions 5,7) are not. This confirms the importance of the OH group at the 3-position. However, the synthetic flavonol TUM 9761 and 3-hydroxyflavone (OH group only at position 3) are poor scavengers. Based on these results, the structure-activity relationship on the peroxynitrite scavenging activity of flavonols was refined. The catechol in ring B remains important. Also the 3-OH group remains important, but the activity of this pharmacophore is influenced by the substituents at position 5 and at position 7.