CONDENSED TANNIN STRUCTURAL CHEMISTRY Ann E.Hagerman ©1arch28.2002 Proanthocyanidins(condensed tannins)are polymeric flavanoids.The flavanoids are a diverse group of metabolites based on a heterocyclic ring system derived from phenylalanine(B)and polyketide biosynthesis(A).Although the biosynthetic pathways for flavanoid synthesis are well understood,the steps leadin condensation and polymerization have not been elucidated The flavanoid skeleton he standard letters to identify the r and the numbering system are shown here The mo t widely studied cond on the fla van-3-ols (-)-epicat and (+ epicatechin catechin Flavan-3-ols Addition of a third phenolic group on the B ring yields epigallocatechin and gallocatechin Much less c common are flav an-3-ols with only ngle phenolic grov on the B ring. respectively). CONDENSED TANNIN STRUCTURAL CHEMISTRY Ann E. Hagerman © March 28, 2002 Proanthocyanidins (condensed tannins) are polymeric flavanoids. The flavanoids are a diverse group of metabolites based on a heterocyclic ring system derived from phenylalanine (B) and polyketide biosynthesis (A). Although the biosynthetic pathways for flavanoid synthesis are well understood, the steps leading to condensation and polymerization have not been elucidated. The flavanoid skeleton, the standard letters to identify the rings, and the numbering system are shown here. The most widely studied condensed tannins are based on the flavan-3-ols (-)-epicatechin and (+)- catechin. Addition of a third phenolic group on the B ring yields epigallocatechin and gallocatechin. Much less common are flavan-3-ols with only a single phenolic group on the B ring, para to C-2 (epiafzelechin, afzelechin with stereochemistry corresponding to epicatechin, catechin respectively). 7 6 5 8 4 3 2 O A B HO O OH OH OH OH epicatechin HO O OH OH OH OH catechin Flavan-3-ols