A-Type Proanthocyanidins from Lychee Seeds and Their Antioxidant and Antiviral Activities

Two new A-type trimeric proanthocyanidins with two doubly bonded interflavanoid linkages, litchitannin A1 [epicatechin-(2 beta -> O -> 7,4 beta -> 6)-epicatechin-(2 beta -> O -> 7,4 beta -> 8)-catechin] (1) and litchitannin A2 [epicatechin-(2 beta -> O -> 7,4 beta -> 6)-epicatechin-(2 beta -> O -> 7,4 beta -> 6)-epicatechin] (2), were isolated from lychee (Litchi chinensis Sonn. cv. Heiye) seeds together with aesculitannin A (3), epicatechin-(2 beta -> O -> 7,4 beta -> 8)-epiafzelechin-(4 alpha -> 8)-epicatechin (4), proanthocyanidin A1 (5), proanthocyanidin A2 (6), proanthocyanidin A6 (7), epicatechin-(7,8-bc)-4 beta-(4-hydroxyphenyl)-dihydro-2(3H)-pyranone (8), and epicatechin (9). Their structures were elucidated on the basis of spectroscopic and chemical evidence. It is the first time that compounds 1-4, 7, and 8 have been reported in this species. Compounds 1-9 showed more potent antioxidant activity than L-ascorbic acid with ferric reducing antioxidant power (FRAP) values of 3.71-24.18 mmol/g and IC50 values of 5.25-20.07 mu M toward DPPH radicals. Moreover, litchitannin A2 (2) was found to exhibit in vitro antiviral activity against coxsackie virus B3 (CVB3) and compounds 3 and 6 displayed antiherpes simplex virus 1 (HSV-1) activity.