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

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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 O2− 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 O2−-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.
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Structural Characteristics for Superoxide Anion Radical Scavenging and Productive Activities of Green Tea Polyphenols Including Proanthocyanidin Dimers

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