Phytochemical and Antioxidant Investigation of Tribulus terrestris
Tribulus terrestris L. is a well known and widely distributed species of the genus Tribulus . The phytochemical investigation of the aerial parts of T. terrestris led to the isolation of two new oligosaccharides (1, 2) and a new stereoisomer of di-p-coumaroylquinic acid (3) along with five known compounds. The structures of the compounds were established as O-β-D-fructofuranosyl-(2 – 6)-α-D-glucopyranosyl-(1 – 6)-β-D-fructofuranosyl-(2 – 6)-β-D-fructo-furanosyl-(2 – 1)-α-D-glucopyranosyl-(6 – 2)-β-D-fructofuranoside (1), O-α-D-glucopyranosyl-(1 – 4)-α-D-glucopyranosyl-(1 – 4)-α-D-glucopyranosyl-(1 – 2)-β-D-fructofuranoside (2), 4,5-di-p-cis-coumaro-ylquinic acid (3), 5-p-cis-coumaroyl-quinic acid, 4,5-di-p-trans-coumaroylquinic acid (3), 5-p-trans-coumaroylquinic acid, diosgenin-3-O-α-L-rhamno-pyranosyl-(1 – 4)-β-D-gluco-pyranoside and dioscin by different spectroscopic methods including 1D- (1 H, 13C and DEPT) and 2D-NMR (COSY, HMQC and HMBC) experiments as well as HR-ESI-MS analysis. All the isolated compounds, except dioscin, are reported for the first time from the family Zygophyllaceae. In addition, this is the first report for the complete NMR spectral data of the known 4,5-di-p-trans-coumaroylquinic acid. The antioxidant activity represented as DPPH free radical scavenging activity was investigated revealing that the di-p-coumaroylquinic acid derivatives possess potent antioxidant activity and so could be considered to be the major constituents contributing to the antioxidant effect of the plant.
Acknowledgements: We are thankful to Dr. Bharthi Avula for HRESMS. IIA is thankful to the Egyptian government for funding. References:  Kostova I, et al. (2005) Phytochem Rev, 4: 111 – 137.