Dehydrodicatechin from -catechin

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). 

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... 

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],... 

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