Two-electron electrochemical oxidation of quercetin and kaempferol changes only the flavonoid C-ring

Lars Jørgensen, Claus Cornett, Ulla Justesen, Leif H. Skibsted, Lars Ove Dragsted

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

Bulk electrolysis of the antioxidant flavonoids quercetin and kaempferol in acetonitrile both yield a single oxidation product in two-electron processes. The oxidation products are more polar than their parent compounds, with an increased molecular weight of 16g/mol, and were identified as 2-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxy-3 (2H)-benzofuranone and 2-(4-hydroxybenzoyl)-2,4,6-trihydroxy-3(2H)-benzofuranone for quercetin and kaempferol, respectively. Two-electron oxidation of the parent flavonoid is suggested to yield a 3,4-flavandione with unchanged substitution pattern in the A- and B-ring, which may rearrange to form the substituted 3(2H)-benzofuranone through the chalcan-trione ring-chain tautomer. The acidity of the 3-OH group is suggested to determine the fate of the flavonoid phenoxyl radical originally formed by one-electron oxidation, as no well-defined oxidation product of luteolin (lacking the 3-OH group) could be isolated despite rather similar half-peak potentials: E-p/2 = 0.97 V, 0.98 V and 1.17 V vs. NHE for quercetin, kaempferol and luteolin, respectively, as measured by cyclic voltammetry in acetonitrile.
Original languageEnglish
JournalFree Radical Research
Volume29
Issue number4
Pages (from-to)339-350
ISSN1071-5762
DOIs
Publication statusPublished - 1998

Keywords

  • 2-(3,4-dihydroxybenzoyl)-2,4,6-trihydroxy-3(2H)-benzofuranone
  • quercetin
  • oxidation product
  • kaempferol
  • 2-(4-hydroxybenzoyl)-2,4,6-trihydroxy-3(2H)-benzofuranone
  • electrochemistry

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