title: Structure-antioxidant activity relationships of flavonoids: a re-examination.
abstract: The antioxidant and prooxidant activities of flavonoids belonging to several classes were studied to establish their structure-activity relationships against different oxidants. Special attention was paid to the flavonoids quercetin (flavone), taxifolin (flavanone) and catechin (flavanol), which possess different basic structures but the same hydroxylation pattern (3,5,7,3'4'-OH). It was found that these three flavonoids exhibited comparable antioxidant activities against different oxidants leading to the conclusion that the presence of ortho-catechol group (3',4'-OH) in the B-ring is determinant for a high antioxidant capacity. The flavone kaempferol (3,5,7,4'-OH), however, in spite of bearing no catechol group, also presents a high antioxidant activity against some oxidants. This fact can be attributed to the presence of both 2,3-double bond and the 3-hydroxyl group, meaning that the basic structure of flavonoids becomes important when the antioxidant activity of B-ring is small.
authors.affiliation: Departamento de Química e Bioquímica, Faculdade de Ciências da Universidade de Lisboa, 1749-016 Lisboa, Portugal.
authors.forename: M Manuela
authors.initials: MM
authors.lastname: Silva
authors.forename: Marta R
authors.initials: MR
authors.lastname: Santos
authors.forename: Gonçalo
authors.initials: G
authors.lastname: Caroço
authors.forename: Rui
authors.initials: R
authors.lastname: Rocha
authors.forename: Gonçalo
authors.initials: G
authors.lastname: Justino
authors.forename: Lurdes
authors.initials: L
authors.lastname: Mira
mesh_terms: D000578:Amidines / Q000378:metabolism; D000975:Antioxidants / Q000494:pharmacology*; D001205:Ascorbic Acid / Q000494:pharmacology; D001713:Biphenyl Compounds; D002392:Catechin / Q000494:pharmacology*; D004492:Edetic Acid / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D044948:Flavonols; D005609:Free Radicals / Q000378:metabolism; D007501:Iron / Q000494:pharmacology; D044949:Kaempferols; D008081:Liposomes / Q000378:metabolism; D008786:Metmyoglobin / Q000378:metabolism; D010851:Picrates / Q000378:metabolism; D011794:Quercetin / Q000031:analogs & derivatives* / Q000494:pharmacology*; D013329:Structure-Activity Relationship
chemical_list: D000578:Amidines; D000975:Antioxidants; D001713:Biphenyl Compounds; D005419:Flavonoids; D044948:Flavonols; D005609:Free Radicals; D044949:Kaempferols; D008081:Liposomes; D010851:Picrates; D008786:Metmyoglobin; C006552:kaempferol; C046728:2,2'-azobis(2-amidinopropane); D002392:Catechin; D004492:Edetic Acid; D011794:Quercetin; C003377:taxifolin; C004931:1,1-diphenyl-2-picrylhydrazyl; D007501:Iron; D001205:Ascorbic Acid