Tannins and Related Compounds. LXIX.1) 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 3-0-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. © 1988, The Pharmaceutical Society of Japan. All rights reserved.