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DPPH (=2,2-diphenyl-1-picrylhydrazyl=2,2-diphenyl-1-(2,4,6-trinitrophenyl)hydrazyl) radical-scavenging reaction of protocatechuic acid esters (=3,4-dihydroxybenzoates) in alcohols : Formation of bis-alcohol adduct

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Title: DPPH (=2,2-diphenyl-1-picrylhydrazyl=2,2-diphenyl-1-(2,4,6-trinitrophenyl)hydrazyl) radical-scavenging reaction of protocatechuic acid esters (=3,4-dihydroxybenzoates) in alcohols : Formation of bis-alcohol adduct
Authors: Saito, Shizuka Browse this author
Gao, Hong Browse this author
Kawabata, Jun Browse this author →KAKEN DB
Keywords: Antioxidant
DPPH Radical
Protocatechuic esters
Radical-scavenging mechanism
Alcohol adduct
Issue Date: 19-Apr-2006
Publisher: Wiley-VCH Verlag Berlin
Journal Title: HELVETICA CHIMICA ACTA
Volume: 89
Issue: 4
Start Page: 821
End Page: 831
Publisher DOI: 10.1002/hlca.200690074
Abstract: Protocatechuic acid esters (=3,4-dihydroxybenzoates) scavenge ca. 5 equiv. of radical in alcoholic solvents. whereas they consume only 2 equiv. of radical in nonalcoholic solvents. While the high radical-scavenging activity of protocatechuic acid esters in alcoholic solvents as compared to that in nonalcoholic solvents is due to a nucleophilic addition of an alcohol molecule at C(2) of an intermediate o-quinone structure, thus regenerating a catechol (=benzene-1,2-diol) structure, it is still unclear why protocatechuic acid esters scavenge more than 4 equiv. of radical (C(2) refers to the protocatechuic acid numbering). Therefore, to elucidate the oxidation mechanism beyond the formation of the C(2) alcohol adduct, 3,4-dihydroxy-2-methoxybenzoic acid methyl ester (4), the C(2) MeOH adduct, which is ail oxidation product of methyl protocatechuate (1) in MeOH, was oxidized by the DPPH radical (=2,2diphenyl-1-picrylhydrazyl) or o-chloranil (=3 4,5,6-tetrachlorocyclohexa-35-diene-1,2-dione) in CD3- OD/(D-6)acetone 3: 1). The oxidation mixtures were directly analyzed by NMR. Oxidation with both the DPPH radical and o-chloranil produced a C(2),C(6) bis-methanol adduct (7), which could scavenge additional 2 equiv. of radical. Calculations of LUMO electron densities of o-quinones corroborated the regioselective nucleophilic addition of alcohol molecules with o-quinones. Our results strongly suggest that the regeneration of a catechol structure via a nucleophilic addition of ail alcohol molecule with a o-quinone is a key reaction for the high radical-scavenging activity of protocatechuic acid esters in alcoholic solvents.
Relation: http://www.interscience.wiley.com/
Type: article (author version)
URI: http://hdl.handle.net/2115/14399
Appears in Collections:農学院・農学研究院 (Graduate School of Agriculture / Faculty of Agriculture) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 川端 潤

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