title: Oxidative cascade reactions yielding polyhydroxy-theaflavins and theacitrins in the formation of black tea thearubigins: evidence by tandem LC-MS.
abstract: LC-MS(n) and direct infusion-MS(n) have been applied for the first time to the characterisation of crude thearubigins isolated from black tea. The data generated have been used to test two hypotheses of thearubigin structure: (i) that a significant fraction of the thearubigins consist of polyhydroxylated derivatives of the better-known catechin dimers (theaflavins, theaflavin mono- and di-gallates, theacitrins) in redox equilibrium with their associated quinones; and (ii) that a significant fraction of the thearubigins consist of dicarboxylic acids generated by oxidative cleavage of aromatic diols. The data were consistent with the polyhydroxylation hypothesis and did not support the dicarboxylic acid hypothesis. Evidence is presented for the presence in crude thearubigins of at least 29 hydroxylated theaflavins (with between one and six oxygen insertions), at least 12 theaflavin mono-gallates (with between one and six oxygen insertions), at least nine theaflavin di-gallates (with between one and four oxygen insertions), and at least ten theacitrin mono-gallates (with between one and four oxygen insertions). Evidence is also presented for at least ten mono- or di-quinone forms of the parent compounds and hydroxylated derivatives in each of these homologous series. A general method for the analysis of complex mixtures by tandem LC-MS is furthermore introduced and established.
authors.affiliation: Functional Materials and Nanomolecular Science Research Centre, Jacobs University Bremen, 28759 Bremen, Germany. n.kuhnert@jacobs-university.de
authors.forename: Nikolai
authors.initials: N
authors.lastname: Kuhnert
authors.forename: Michael N
authors.initials: MN
authors.lastname: Clifford
authors.forename: Anja
authors.initials: A
authors.lastname: Müller
mesh_terms: D016227:Benzoquinones / Q000032:analysis / Q000737:chemistry; D044946:Biflavonoids / Q000032:analysis / Q000737:chemistry*; D002392:Catechin / Q000031:analogs & derivatives* / Q000032:analysis / Q000737:chemistry; D002853:Chromatography, Liquid; D019281:Dimerization; D005707:Gallic Acid / Q000031:analogs & derivatives* / Q000032:analysis / Q000737:chemistry; D006900:Hydroxylation; D013058:Mass Spectrometry; D018384:Oxidative Stress / Q000187:drug effects*; D010100:Oxygen / Q000737:chemistry; D010636:Phenols / Q000032:analysis / Q000737:chemistry*; D010936:Plant Extracts / Q000032:analysis / Q000737:chemistry*; D059808:Polyphenols; D013662:Tea / Q000737:chemistry*
chemical_list: D016227:Benzoquinones; D044946:Biflavonoids; D010636:Phenols; D010936:Plant Extracts; D059808:Polyphenols; D013662:Tea; C086701:thearubigin; C088983:theaflavine gallate; C004532:quinone; D005707:Gallic Acid; D002392:Catechin; D010100:Oxygen