TY - JOUR
T1 - Flavonoid oxidation by the radical generator AIBN
T2 - A unified mechanism for quercetin radical scavenging
AU - Krishnamachari, Venkat
AU - Levine, Lanfang H.
AU - Paré, Paul W.
PY - 2002/7/17
Y1 - 2002/7/17
N2 - Four oxidized flavonoid derivatives generated from reacting quercetin (a pentahydroxylated flavone) with the peroxyl radical generator 2,2′-azobis-isobutyronitrile (AIBN) were isolated by chromatographic methods and identified by NMR and MS analyses. Compounds included 2-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxy-3(2H)-benzofuranone (2); 1,3,11a-trihydroxy-9-(3,5,7-trihydroxy-4H-1-benzopyran-4-on-2-yl)-5a-(3, 4-dihydroxyphenyl)-5,6,11-hexahydro-5,6,11-trioxanaphthacene-12-one (3); 2-(3,4-dihydroxybenzoyloxy)-4,6-dihydroxybenzoic acid (4); and methyl 3,4-dihydroxyphenylglyoxylate (5). Product ratios under different hydrogen ion concentrations and external nucleophiles revealed that two of the products, namely the substituted benzofuranone (2) and the depside (4), are generated from a common carbocation intermediate. Indirect evidence for the operation of a cyclic concerted mechanism in the formation of the dimeric product (3) is provided. The identification of these products supports the model that the principal site of scavenging reactive oxygen species (ROS) in quercetin is the ̂-dihydroxyl substituent in the B-ring, as well as the C-ring olefinic linkage.
AB - Four oxidized flavonoid derivatives generated from reacting quercetin (a pentahydroxylated flavone) with the peroxyl radical generator 2,2′-azobis-isobutyronitrile (AIBN) were isolated by chromatographic methods and identified by NMR and MS analyses. Compounds included 2-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxy-3(2H)-benzofuranone (2); 1,3,11a-trihydroxy-9-(3,5,7-trihydroxy-4H-1-benzopyran-4-on-2-yl)-5a-(3, 4-dihydroxyphenyl)-5,6,11-hexahydro-5,6,11-trioxanaphthacene-12-one (3); 2-(3,4-dihydroxybenzoyloxy)-4,6-dihydroxybenzoic acid (4); and methyl 3,4-dihydroxyphenylglyoxylate (5). Product ratios under different hydrogen ion concentrations and external nucleophiles revealed that two of the products, namely the substituted benzofuranone (2) and the depside (4), are generated from a common carbocation intermediate. Indirect evidence for the operation of a cyclic concerted mechanism in the formation of the dimeric product (3) is provided. The identification of these products supports the model that the principal site of scavenging reactive oxygen species (ROS) in quercetin is the ̂-dihydroxyl substituent in the B-ring, as well as the C-ring olefinic linkage.
KW - AIBN
KW - Antioxidant
KW - Flavonols
KW - Oxidizing agents
KW - Peroxyl radicals
KW - Quercetin
UR - http://www.scopus.com/inward/record.url?scp=0037125114&partnerID=8YFLogxK
U2 - 10.1021/jf020045e
DO - 10.1021/jf020045e
M3 - Article
C2 - 12105970
AN - SCOPUS:0037125114
SN - 0021-8561
VL - 50
SP - 4357
EP - 4363
JO - Journal of Agricultural and Food Chemistry
JF - Journal of Agricultural and Food Chemistry
IS - 15
ER -