New antioxidant C-glucosylxanthones from the stems of Arrabidaea samydoides

Three new C-glucosylxanthones, 2-(2'-O-trans-caffeoyl)-C-beta-d-glucopyranosyl-1,3,6,7-tetrahydroxyxanthone (1), 2-(2'-O-trans-cinnamoyl)-C-beta-d-glucopyranosyl-1,3,6,7-tetrahydroxyxanthone (2), and 2-(2'-O-trans-coumaroyl)-C-beta-d-glucopyranosyl-1,3,6,7-tetrahydroxyxanthone (3), were isolated from the stems of Arrabidaea samydoides, in addition to three known C-glucosylxanthones, mangiferin (4), 2-(2'-O-benzoyl)-C-beta-d-glucopyranosyl-1,3,6,7-tetrahydroxyxanthone (5), and muraxanthone (6). Their chemical structures were assigned on the basis of MS and 1D and 2D NMR experiments. Xanthones 1-6 showed moderate free radical scavenging activity against 1,1-diphenyl-2-picrylhydrazyl (DPPH) as well as antioxidant activity evidenced by redox properties measured on ElCD-HPLC.