Chemical constituents from Tribulus terrestris and screening of their antioxidant activity

Two oligosaccharides (1,2) and a stereoisomer of di-p-coumaroylquinic acid (3) were isolated from the aerial parts of Tribulus terrestris along with five known compounds (4-8). The structures of the compounds were established as O-beta-D-fructofuranosyl-(2 -> 6)-alpha-D-glucopyranosyl-(1 -> 6)-beta-D-fructofuranosyl-(2 -> 6)-beta-D-fructofuranosyl-(2 -> 1)-alpha-D-glucopyranosyl-(6 -> 2)-beta-D-fructofuranoside (1), O-alpha-D-glucopyranosyl-(1 -> 4)-alpha-D-glucopyranosyl-(1 -> 4)-alpha-D-glucopyranosyl-(1 -> 2)-beta-D-fructofuranoside (2), 4,5-di-p-cis-coumaroylquinic acid (3) by different spectroscopic methods including 1D NMR (H-1, C-13 and DEPT) and 2D NMR (COSY, TOCSY, HMQC and HMBC) experiments as well as ESI-MS analysis. This is the first report for the complete NMR spectral data of the known 4,5-di-p-trans-coumaroylquinic acid (4). The antioxidant activity represented as DPPH free radical scavenging activity was investigated revealing that the di-p-coumaroylquinic acid derivatives possess potent antioxidant activity so considered the major constituents contributing to the antioxidant effect of the plant. (c) 2013 Elsevier Ltd. All rights reserved.