Dehydrodicatechin

Sun, W. and Miller, J.M., Tandem mass spectrometry of the B-type procyanidins in wine and B-type dehydrodicatechins in an autoxidation mixture of (+)-catechin and (-)-epicatechin, J. Mass Spectrom., 38, 438, 2003. 

The electrophilic primary and secondary quinones undergo addition of nucleophiles, including flavonoids. For instance, nucleophilic addition of catechin to its enzymatically generated quinone yielded a catechin dimer in which the catechin moieties are linked through a C6 C8 biphenyl linkage. This B-type dehydrodicatechin further oxidized to yellow pigments. Additional dehydrodicatechins arise from radical coupling of the catechin semi-quinones formed by retro-disproportionation, in which the catechin moieties are linked... 

Havonoid autoxidation in wine is a slow process but its rate increases with pH. For instance, products arising from addition of malvidin 3-glucoside onto epicate-chin quinone were observed only at pH 4 and above (Duenas et al. 2006a). Oxidation of flavanols and formation of B-type and A-type dehydrodicatechins was observed in the wine pH range (Oszmianski et al. 1996). When catalysts such as metal ions are present, oxidation of tartaric acid and subsequent formation of xanthylium pigments compete with autoxidation reactions. 

Class in plant peroxidases, such as that purified from strawberries, are able to oxidize (+)-catechin with ki values of 0.57 pM s at pH 5.0 [36]. The peroxidase-mediated oxidation of (+)-catechin leads to the formation of dimers such as dehydrodicatechin A and B4, trimers, tetramers and oligomers of different degrees of polymerization [146,147],... 

Dehydrodicatechin B4 (XLIII), a dimer resulting from (+)-catechin head to tail polymerization (Scheme XXI, continuation), is the precursor of dehydrodicatechin A (XLIV), which is derived from the former through a single step involving enzymatic oxidation followed by an internal stabilization via two intramolecular nucleophilic additions (Scheme XXII). 

NMR, UV-vis, and mass spectroscopies [38]. A detailed NMR analysis provided a structural hypothesis for five resulting products. The colorless dimers are dehydrodicatechins of type B with C - O and C - C interflavin Unkages. Two yellow dimers correspond to dehydrodicatechin A and to a structure of quinone-methide-type. 

The reaction products obtained by the HRP-catalyzed oxidative coupling of catechin were analyzed by reversed-phase and size-exclusion chromatographies [42]. The products were dehydrodicatechin A and ohgomers with DP equal or greater than 5. The joint use of both chromatographies permits the qualitative and quantitative identification of the product mixtures. 

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