title: Stereochemistry of the Black Tea Pigments Theacitrins A and C.
abstract: Theacitrins A-C are yellow pigments of black tea that are produced by oxidative coupling of gallocatechins, i.e., flavan-3-ols with pyrogallol-type B-rings. However, their stereostructures have not yet been determined. In this study, DFT calculations of NMR chemical shifts of theacitrin C (1) and TDDFT calculations of the ECD spectra of theacitrinin A (5), a degradation product of theacitrin C (1), were used to determine the stereostructure of the theacitrins. Furthermore, the preparation of theacitrins A (4) and C (1) by enzymatic oxidation of an epigallocatechin (7) and epigallocatechin-3-O-gallate (2) mixture confirmed their structural relationship.
authors.affiliation: Graduate School of Biomedical Sciences, Nagasaki University , 1-14 Bunkyo-machi, Nagasaki 852-8521, Japan.
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Matsuo
authors.affiliation: Graduate School of Biomedical Sciences, Nagasaki University , 1-14 Bunkyo-machi, Nagasaki 852-8521, Japan.
authors.forename: Keita
authors.initials: K
authors.lastname: Okuda
authors.affiliation: Graduate School of Biomedical Sciences, Nagasaki University , 1-14 Bunkyo-machi, Nagasaki 852-8521, Japan.
authors.forename: Hitomi
authors.initials: H
authors.lastname: Morikawa
authors.affiliation: Graduate School of Biomedical Sciences, Nagasaki University , 1-14 Bunkyo-machi, Nagasaki 852-8521, Japan.
authors.forename: Ryosuke
authors.initials: R
authors.lastname: Oowatashi
authors.affiliation: Graduate School of Biomedical Sciences, Nagasaki University , 1-14 Bunkyo-machi, Nagasaki 852-8521, Japan.
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Saito
authors.affiliation: Graduate School of Biomedical Sciences, Nagasaki University , 1-14 Bunkyo-machi, Nagasaki 852-8521, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Tanaka
mesh_terms: D028241:Camellia sinensis; D002392:Catechin / Q000031:analogs & derivatives* / Q000737:chemistry* / Q000494:pharmacology; D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular; D010084:Oxidation-Reduction; D010860:Pigments, Biological / Q000737:chemistry*; D059808:Polyphenols; D013662:Tea / Q000737:chemistry*
chemical_list: D010860:Pigments, Biological; D059808:Polyphenols; D013662:Tea; C000608631:theacitrin A; C551167:theacitrin C; D002392:Catechin; C045651:epigallocatechin gallate; C057580:gallocatechol