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 (O2-) scavenging and productive activities of green tea polyphenols. (-)-Epicatechin 3-O-gallate (5), (-)-epigallocatechin (6), (-)-epigallocatechin 3-O-gallate (7), (+)-gallocatechin-(4α→8′)-epigallocatechin (8), and (-)-epigallocatechin-(2β→O→7′, 4β→8′)- epicatechin 3′-O-gallate (9) were isolated from the tea plant Camellia sinensis L. (+)-Epigallocatechin-(2β→O→7, 4β→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≈11≈8, 7, 10, 2≈9, 5≈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 O2--productive activity partially counteracted O2--scavenging activity. However, such structural characteristics appeared to enhance the scavenging activity, accordingly the polyphenols in effect served as O2--scavengers in descending order 9≈7, 2, 11, 8, 10, 3≈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. © 2010 Pharmaceutical Society of Japan.