Flavonoids from the Pericarps of Litchi chinensis

A new methylene-linked flavan-3-ol dimer, bis(8-epicatechinyl)methane (1), was isolated from the pericarps of Litchi chinensis Sonn. (Sapindaceae), together with dehydrodiepicatechin A (2), proanthocyanidin A1 (3), proanthocyanidin A2 (4), (-)-epicatechin (5), 8-(2-pyrrolidinone-5-yl)-(-)-epicatechin (6), (-)-epicatechin 8-C-beta-D-glucopyranoside (7), naringenin 7-O-(2,6-di-O-alpha-L-rhamnopyranosyl)-beta-D-glucopyranoside (8), and rutin (9). It was the first report of compound 2 as a natural product and compounds 6-8 from this species. Compounds 1, 2, and 6-8 were evaluated for antioxidant activity. The ferric reducing antioxidant powers (FRAP) of compounds 1 and 6 were comparable to that of L-ascorbic acid, and the scavenging activities of compounds 1, 2, 6, and 7 toward 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals and 2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonic acid) radical cations were more potent than those of L-ascorbic acid; compound 8 was weak in FRAP and DPPH assays.