Tannins and related compounds. XV. A new class of dimeric flavan-3-ol gallates, theasinensins A and B, and proanthocyanidin gallates from green tea leaf

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.