Tannins and related compounds. LXIX. Isolation and structure elucidation of B,B'-linked bisflavanoids, theasinensins D-G and oolongtheanin from oolong tea. (2).

Abstract

Chemical examination of the aqueous acetone extract of commercial oolong tea has led to the isolation of four new theasinensins D-G, and a new type of dimeric flavan-3-ol named oolong-theanin, together with previously reported theasinensins A, B, and C. On the basis of chemical and spectroscopic evidence, theasinensins D and E were characterized as atropisomers (4 and 5) of theasinensins A (1) and C (3), respectively, while theasinensins F and G were shown to be B, B'-linked bisflavanoids (6 and 7) consisting of (-)-epicatechin 3-O-gallate and (-)-epigallocatechin 3-O-gallate units, in which the biphenyl bonds possess S- and R-chiralities, respectively. Similarly, oolongtheanin was characterized as a novel metabolite (8), probably derived from theasinensins by oxidation of one of the B-rings.