title: Oxidative coupling of the pyrogallol B-ring with a galloyl group during enzymatic oxidation of epigallocatechin 3-O-gallate.
abstract: In order to clarify the mechanism for formation of catechin oligomers during the fermentation stage of black tea manufacture, epigallocatechin-3-O-gallate, the most abundant tea flavanol in fresh tea leaves, was enzymatically oxidized and the resulting unstable quinone metabolites were converted to phenazine derivatives by treatment with o-phenylenediamine. In addition to formation of monomeric and dimeric derivatives, four trimeric derivatives were isolated whose structures were determined by application of spectroscopic methods. The derivatives differed from each other in the location of the phenazine moieties and in the atropisomerism of the biphenyl bond. The results suggested that oxidative coupling of the galloyl group with the B-ring proceeds by a quinone dimerization mechanism similar to that for production of theasinensins.
authors.affiliation: Graduate School of Biomedical Sciences, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki 852-8521, Japan.
authors.forename: Yan
authors.initials: Y
authors.lastname: Li
authors.forename: Takashi
authors.initials: T
authors.lastname: Tanaka
authors.forename: Isao
authors.initials: I
authors.lastname: Kouno
mesh_terms: D028241:Camellia sinensis / Q000737:chemistry*; D002392:Catechin / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D008956:Models, Chemical; D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular; D010084:Oxidation-Reduction; D010655:Phenylenediamines / Q000737:chemistry / Q000378:metabolism; D010936:Plant Extracts / Q000378:metabolism; D011748:Pyrogallol / Q000737:chemistry* / Q000378:metabolism; D031989:Pyrus / Q000737:chemistry / Q000201:enzymology
chemical_list: D010655:Phenylenediamines; D010936:Plant Extracts; D011748:Pyrogallol; C034193:1,2-diaminobenzene; D002392:Catechin; C045651:epigallocatechin gallate