The Contribution of the Pyrogallol Moiety to the Superoxide Radical Scavenging Activity of Flavonoids.

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  • Furuno Koji
    Faculty of Pharmacy and Pharmaceutical Sciences, Fukuyama University
  • Akasako Toyokazu
    Faculty of Pharmacy and Pharmaceutical Sciences, Fukuyama University
  • Sugihara Narumi
    Faculty of Pharmacy and Pharmaceutical Sciences, Fukuyama University

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  • The Contribution of the Pyrogallol Moiety to the Superoxide Radical Scavenging Activity of f1avonoids
  • Contribution of the Pyrogallol Moiety to the Superoxide Radical Scavenging Activity of f1avonoids

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Sixteen flavonoids including flavonols, flavones, flavanonol and catechins, and five aromatic compounds were examined for their ability to scavenge superoxide radical (O2−) generated enzymatically in a xanthin–xanthinoxidase system and non-enzymatically in a phenazine methosulfate–NADH system. Pyrogallol, gallic acid and its ester, were much more efficient in scavenging O2− than catechol. The superiority of pyrogallol over catechol in the flavonoidal nucleus is apparent from the much higher O2− scavenging activity of myricetin and epigallocatechin, which contain 3′, 4′, 5′-trihydroxyl substitution in the B-ring, compared to quercetin and epicatechin, which contain 3′, 4′-dihydroxyl substitution, respectively. The strong O2− scavenging ability of pyrogallol appears to function even in the A-ring, as in baicalein, and also in the form of a pyrogalloyl ester at the C-3 position in the C-ring, as in epicatechin gallate and epigallocatechin gallate. It can be concluded that the pyrogallol moiety is an active component of flavonoids for displaying high O2− scavenging activity. Flavonoids and aromatics were also examined to correlate their O2− scavenging activity with their oxidizability, which was measured on the basis of electrochemical redox potential and the reducing ability of the Cu2+ ion. Aromatics such as pyrogallol, gallic acid and its ester, and flavonoids such as baicalein, epicatechin gallate and epigallocatechin gallate, in which the O2− scavenging activity is enhanced by the presence of a pyrogallol moiety which does not belong to the B-ring, reduced the correlation between the higher O2− scavenging activity and the lower redox potential. The O2− scavenging activity was well correlated with the Cu2+ reducing ability of flavonoids and aromatics.

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