Structural Characteristics for Superoxide Anion Radical Scavenging and Productive Activities of Green Tea Polyphenols Including Proanthocyanidin Dimers

The purpose of this paper is to report structural characteristics for superoxide anion radical (02) scavenging and productive activities of green tea polyphenols. (-)-Epicatechin 3-O-gallate (5), (-)-epigallocatechin (6), (-)-epigallocatechin 3-O-gallate (7), (+)-gallocatechin-(4 alpha -> 8')-epigallocatechin (8), and (-)-epigallocatechin-(2 beta -> O ->', 4 beta -> 8')-epicatechin 3'-O-gailate (9) were isolated from the tea plant Camellia sinensis L. (+)-Epigallocatechin-(2 beta -> O -> 7, 4 beta -> 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 approximate to 11 approximate to 8, 7, 10, 2 approximate to 9, 5 approximate to 4. 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 approximate to 7, 2, 11, 89 10, 3 approximate to 4. 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.