Flavanoid-based tannins

C.I. Natural Brown 3, 75250 (catechu) has the basic structure of catechin (2) and is a condensed tannin, e.g., gambier from leaves and twigs of the Uncaria gambler bush. Many of these tanning agents are based on a catechin flavanoid. 

Figure 6 The flavanoid ring structure on which condensed tannins are based...

The previous section (7.6) described the chemistry of the catechins and oligomeric proanthocyanidins. The historical steps that brought Bate-Smith and Swain, Roux, and other early workers to the realization that condensed tannins are essentially polymers based on the same flavanoid units is now a familiar story (55, 57, and references therein). However, it awguted the modern chemical methodology of the 1980 s to provide an unequivocal demonstration of the veracity of these predictions. 

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