title: The contribution of the pyrogallol moiety to the superoxide radical scavenging activity of flavonoids.
abstract: 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.
authors.affiliation: Faculty of Pharmacy and Pharmaceutical Sciences, Fukuyama University, Hiroshima, Japan. furuno@fupharm.fukuyama-u.ac.jp
authors.forename: Koji
authors.initials: K
authors.lastname: Furuno
authors.forename: Toyokazu
authors.initials: T
authors.lastname: Akasako
authors.forename: Narumi
authors.initials: N
authors.lastname: Sugihara
mesh_terms: D003300:Copper / Q000737:chemistry; D005419:Flavonoids / Q000737:chemistry*; D016166:Free Radical Scavengers / Q000737:chemistry*; D010084:Oxidation-Reduction; D011748:Pyrogallol / Q000737:chemistry*; D013481:Superoxides / Q000737:chemistry*
chemical_list: D005419:Flavonoids; D016166:Free Radical Scavengers; D011748:Pyrogallol; D013481:Superoxides; D003300:Copper