Dicaffeoylquinic acid derivatives and flavonoid glucosides from glasswort (Salicornia herbacea L.) and their antioxidative activity

Two novel antioxidant compounds, isoquercitrin 6 ''-O-methyloxalate (6) and methyl 4-caffeoy1-3-dihydrocaffeoyl quinate (salicornate, 7), were isolated from Salicornia herbacea L. Six known compounds were also identified as 3,5-dicaffeoylquinic acid (1), quercetin 3-O-B-D-glucopyranoside (2), 3-caffeoyl-4-dihydrocaffeoylquinic acid (3), methyl 3,5-dicaffeoyl quinate (4), 3.4-dicaffeoylquinic acid (5), and isorhamnetin 3-O-beta-D-glucopyranoside (8). Their chemical structures were determined by spectroscopic data from ESI-MS and NMR. The isolated dicaffeoylquinic acid derivatives (1, 3, 4, 5, and 7) showed similar activities for scavenging 1,1-diphenyl-2-picrylhydrazyl radicals and inhibiting formation of cholesteryl ester hydroperoxide during copper ion-induced rat blood plasma oxidation. The two flavonol glucosides (2 and 6), which have no substitutions in the B ring of their aglycones, also had similar activity. However, compound 8, which has the same structure as 2 except for the presence of a methoxyl group in the C-3' position of the B ring, showed predominantly lower antioxidant activity than the other isolated compounds. (C) 2010 Elsevier Ltd. All rights reserved.