Abstract
A chemical examination of the polypenolic constituents in commercial oolong tea has led to the isolation of a new-flavan-3-ol, two novel dimeric flavan-3-ols named oolonghomobisflavans A and B eight new proanthocyanidins, together with twenty-one known polyphenols including proanthocyanidins, hydrolyzable tannins and red pigments. On the basis of chemical and spectroscopic evidence, the flavan-3-ol has been characterized as 8-C-ascorbyl (-)-epigallocatechin 3-O-gallate (22), while oolonghomobisflavans A (26) and B (27) have been determined to be dimeric flavan-3-ols in which two units are linked through a methylene bridge at the 8, 8'- and 8, 6'-positions, respectively. The structures of the new proanthocyanidins were elucidated mainly by tannase hydrolysis and thiolytic degradtion as epicatechin-(4β→8)-epigallocatechin 3-O-gallate (29), epicatechin 3-O-gallate-(4β→8)-epigallocatechin 3-O-gallate (30), catechin-(4α→8)-epigallocatechin 3-O-gallate (31), prodelphinidin B-4 3'-O-gallate (32), epicatechin 3-O-gallate-(4β→6)-epigallocatechin 3-O-gallate (33), epigallocatechin 3-O-gallate-(4β→6)-epicatechin 3-O-gallate (34), epiafzelechin 3-O-gallate-(4β→6)-epigallocatechin 3-O-gallate (35) and prodelphinidin B-2 3'-O-gallate (36).
