title: Enzymatic oxidation of gallocatechin and epigallocatechin: effects of C-ring configuration on the reaction products.
abstract: Tea leaf is rich in pyrogallol-type catechins, and their oxidation is important in the generation of black tea polyphenols. In the present study, the enzymatic oxidation of three pyrogallol-type catechins, (+)- and (-)-gallocatechins and (-)-epigallocatechin, was compared. The reactions yielded unstable quinone products, which were trapped as condensation products with o-phenylenediamine. The oxidation of (+)-gallocatechin proceeded very slowly compared to the reaction of (-)-epigallocatechin, and yielded a proepitheaflagallin-type dimer as the major product, though oxidation of (-)-epigallocatechin gave predominantly dehydrotheasinensin C. The cis-configuration of the C-3 hydroxyl group and the B-ring of (-)-epigallocatechin was apparently crucial for rapid and selective production of dehydrotheasinensin C. Oxidation of (-)-gallocatechin proceeded in a manner similar to that of (+)-gallocatechin, and produced an enantiomer of the (+)-gallocatechin product. The results suggest that enzymes catalyze oxidation of the pyrogallol B-ring to the o-quinone, with subsequent non-enzymatic coupling reactions proceed under highly steric control.
authors: Graduate School of Biomedical Sciences, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki 852-8521, Japan.
authors: Yosuke
authors: Y
authors: Matsuo
authors: Yuko
authors: Y
authors: Yamada
authors: Takashi
authors: T
authors: Tanaka
authors: Isao
authors: I
authors: Kouno
mesh_terms: D028241:Camellia sinensis / Q000737:chemistry / Q000201:enzymology; D002392:Catechin / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D015394:Molecular Structure; D010084:Oxidation-Reduction; D031989:Pyrus / Q000201:enzymology
chemical_list: D002392:Catechin; C057580:gallocatechol