Flavan

Abstract: Along with four dimeric proanthocyanidin gallates, viz. prodelphinidin B-2 3'-O-gallate (IV) and procyanidins B-2 3, 3'-di-O-gallate (V), B-2 3'-O-gallate (VI) and B-4 3'-O-gallate (VII), two novel dimeric flavan-3-ol gallates (VIII and IX) named theasinensins A and B, in which two flavan units are linked at the B-ring, have been isolated from fresh green tea leaves, and their structures have been established on the basis of spectroscopic evidence in conjunction with enzymatic hydrolyses with tannase. Three new monomeric acylated flavan-3-ols have also been isolated, and their structures were similarly characterized as (-)-epigallocatechin 3-O-p-coumaroate (I), (-)-epigallocatechin 3, 3'-di-O-gallate (II) and (-)-epigallocatechin 3, 4'-di-O-gallate (III). In addition, the occurrence of the known (-)-epicatechin 3-O-gallate (X), (-)-epigallocatechin 3-O-gallate (XI), (+)-catechin (XII), (-)-epicatechin (XIII), (-)-epigallocatechin (XIV) and (-)-epicatechin 3-O-(3-O-methyl)-gallate (XV) in green tea leaves was confirmed.

Abstract: The flavonoids are derived from the flavan or isoflavan skeleton (Fig. 1) and comprise a large group of secondary metabolites from higher plants (Harborne et al. 1975). In the literature the term flavonoid is often used to mean all flavonoids except anthocyanins and for the sake of convenience we have followed this usage. Anthocyanins are 3- or 3,5-glycosides of anthocyanidins (Fig. 2) and include the principal red (R), violet and blue (B) plant pigments (λ 520-545 nm).