title: Two types of oxidative dimerization of the black tea polyphenol theaflavin.
abstract: Theaflavin and its galloyl esters are polyphenolic pigments of black tea. In the course of studies on the oxidation mechanism of tea polyphenols, two theaflavin oxidation products named bistheaflavins A and B were isolated, and their structures were elucidated on the basis of MS and NMR spectroscopic analyses. Treatment of a mixture of (-)-epicatechin and (-)-epigallocatechin with banana fruit homogenate yielded bistheaflavin A together with theaflavin and theanaphthoquinone. The symmetrical structure of bistheaflavin A suggested that this compound was formed by oxidative C [bond] C coupling of two theaflavin molecules. In contrast, theaflavin in phosphate buffer (pH 7.3) was gradually oxidized to give bistheaflavin B and theanaphthoquinone. Bistheaflavin B possesses a bicyclooctane skeleton probably formed by intermolecular cyclization between dehydrotheaflavin and dihydrotheanaphthoquinone.
authors.affiliation: School of Pharmaceutical Sciences, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki 852-8521, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Tanaka
authors.forename: K
authors.initials: K
authors.lastname: Inoue
authors.forename: Y
authors.initials: Y
authors.lastname: Betsumiya
authors.forename: C
authors.initials: C
authors.lastname: Mine
authors.forename: I
authors.initials: I
authors.lastname: Kouno
mesh_terms: D000975:Antioxidants / Q000737:chemistry*; D044946:Biflavonoids; D002392:Catechin; D019281:Dimerization; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D008958:Models, Molecular; D008968:Molecular Conformation; D010084:Oxidation-Reduction; D013662:Tea / Q000737:chemistry*
chemical_list: D000975:Antioxidants; D044946:Biflavonoids; D013662:Tea; C056068:theaflavin; D002392:Catechin