title: Identification of autoxidation oligomers of flavan-3-ols in model solutions by HPLC-MS/MS.
abstract: Autoxidation of flavan-3-ols was carried out in aqueous/methanol model solutions under mildly acidic conditions (pH 6.0), and these autoxidation products were analyzed by using high performance liquid chromatography (HPLC) coupled with tandem mass spectrometry (MS/MS). The results showed that (+)-catechins and (-)-epicatechins generated autoxidation reaction with each other to form a series of oligomers that had the same [M - H](-) molecular ions (MS(1)) as those of natural procyanidins, but had completely different fragment ions (MS(2)). According to MS/MS analysis, the major fragments of these oligomers were derived not only from the retro-Diels-Alder (RDA) dissociations on the C-rings of the flavan-3-ol units, but also from the quinone-methide (QM) cleavage of the interflavan linkages (IFL), and thus they were identified as B-type dehydrodicatechins, B-type dehydrotricatechins and A-type dehydrotricatechins, respectively. The potential structures of their [M - H](-) molecular ions and partial fragment ions were deduced on the basis of the MS/MS characterization and the oxidation of flavan-3-ols in previous reports. Some specific fragment ions were found to be very useful for identifying the autoxidation oligomers (the B-type dehydrodicatechins at m/z 393, the B-type dehydrotricatechins at m/z 681 and the A-type dehydrotricatechins at m/z 725).
authors.affiliation: Centre for Viticulture and Enology, College of Food Science and Nutritional Engineering, China Agricultural University, Beijing 100083, China.
authors.forename: Fei
authors.initials: F
authors.lastname: He
authors.forename: Qiu-Hong
authors.initials: QH
authors.lastname: Pan
authors.forename: Ying
authors.initials: Y
authors.lastname: Shi
authors.forename: Xue-Ting
authors.initials: XT
authors.lastname: Zhang
authors.forename: Chang-Qing
authors.initials: CQ
authors.lastname: Duan
mesh_terms: D002392:Catechin / Q000031:analogs & derivatives / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D006863:Hydrogen-Ion Concentration; D007477:Ions / Q000737:chemistry; D008956:Models, Chemical; D008958:Models, Molecular; D010084:Oxidation-Reduction; D053719:Tandem Mass Spectrometry / Q000379:methods*
chemical_list: D007477:Ions; D002392:Catechin