Identification of autoxidation oligomers of flavan-3-ols in model solutions by HPLC-MS/MS

• Published in: Journal of mass spectrometry. 2009-05, Vol.44 (5), p.633-640
• Main Authors: He, Fei, Pan, Qiu-Hong, Shi, Ying, Zhang, Xue-Ting, Duan, Chang-Qing
• Format: Article
• Language: English
• Subjects: A-type dehydrotricatechin; Analytical chemistry; Autoxidation; B-type dehydrodicatechin; B-type dehydrotricatechin; Catechin - analogs & derivatives; Catechin - chemistry; Chemistry; Chromatographic methods and physical methods associated with chromatography; Chromatography, High Pressure Liquid - methods; Cleavage; Exact sciences and technology; flavan-3-ols; Fragmentation; HPLC-DAD-ESI/MS; Hydrogen-Ion Concentration; Ions - chemistry; Mass spectrometry; Mathematical models; Methyl alcohol; Models, Chemical; Models, Molecular; Molecular ions; Oligomers; Other chromatographic methods; Oxidation-Reduction; Tandem Mass Spectrometry - methods
• ISSN: 1076-5174; 1096-9888; 1096-9888
• DOI: 10.1002/jms.1536

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 (MS¹) as those of natural procyanidins, but had completely different fragment ions (MS²). 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). Copyright © 2008 John Wiley & Sons, Ltd.