title: Structural characteristics for superoxide anion radical scavenging and productive activities of green tea polyphenols including proanthocyanidin dimers.
abstract: The purpose of this paper is to report structural characteristics for superoxide anion radical (O(2(-))) scavenging and productive activities of green tea polyphenols. (-)-Epicatechin 3-O-gallate (5), (-)-epigallocatechin (6), (-)-epigallocatechin 3-O-gallate (7), (+)-gallocatechin-(4alpha-->8')-epigallocatechin (8), and (-)-epigallocatechin-(2beta-->O-->7', 4beta-->8')-epicatechin 3'-O-gallate (9) were isolated from the tea plant Camellia sinensis L. (+)-Epigallocatechin-(2beta-->O-->7, 4beta-->8')-epicatechin (10) was prepared by hydrolyzing 9. The polyphenols, as well as commercially available pyrogallol (1), methyl gallate (2), (+)-catechin (3), (-)-epicatechin (4), and the flavonol myricetin (11), produced O(2(-)) in descending order 1, 6 asymptotically equal to11 asymptotically equal to8, 7, 10, 2 asymptotically equal to9, 5 asymptotically equal to4. In the polyphenols with the pyrogallol-type B-ring and/or galloyl group, electron-withdrawing substituents (carbonyl and ketal carbons) and/or intramolecular hydrogen bonding constituted structural characteristics against the autoxidation reaction. The O(2(-))-productive activity partially counteracted O(2(-))-scavenging activity. However, such structural characteristics appeared to enhance the scavenging activity, accordingly the polyphenols in effect served as O(2(-))-scavengers in descending order 9 asymptotically equal to7, 2, 11, 8, 10, 3 asymptotically equal to4. On the other hand, 6, having no such structural characteristic, acted as a O(2(-))-generator, as well as 1. Further assessments covering tannins (e.g., A-type proanthocyanidin dimer 9) are needed to identify which green tea polyphenols are the most desirable chemopreventive agents.
authors.affiliation: Department of Applied Biological Science, Kagawa University, Kagawa, Japan.
authors.forename: Masashi
authors.initials: M
authors.lastname: Sato
authors.forename: Hajime
authors.initials: H
authors.lastname: Toyazaki
authors.forename: Yu
authors.initials: Y
authors.lastname: Yoshioka
authors.forename: Nobutoshi
authors.initials: N
authors.lastname: Yokoi
authors.forename: Toru
authors.initials: T
authors.lastname: Yamasaki
mesh_terms: D028241:Camellia sinensis / Q000737:chemistry*; D002392:Catechin / Q000737:chemistry* / Q000302:isolation & purification; D005419:Flavonoids / Q000737:chemistry* / Q000302:isolation & purification; D016166:Free Radical Scavengers / Q000737:chemistry* / Q000302:isolation & purification; D008958:Models, Molecular; D015394:Molecular Structure; D010636:Phenols / Q000737:chemistry* / Q000302:isolation & purification; D059808:Polyphenols; D044945:Proanthocyanidins / Q000737:chemistry* / Q000302:isolation & purification; D013481:Superoxides / Q000737:chemistry; D013662:Tea / Q000737:chemistry*
chemical_list: D005419:Flavonoids; D016166:Free Radical Scavengers; D010636:Phenols; D059808:Polyphenols; D044945:Proanthocyanidins; D013662:Tea; D013481:Superoxides; C013221:proanthocyanidin; D002392:Catechin