Antioxidative extracts and phenols isolated from Qinghai-Tibet Plateau medicinal plant Saxifraga tangutica Engl.

Saxifraga tangutica Engl., is a medicinal herb that grows on the Qinghai-Tibet Plateau. Extracts and phenols from the Qinghai population have been subjected to antioxidative assays against DPPH radical-scavenging and reducing power (FRAP). The 50% ethanol extract showed strong antioxidative activity against DPPH and FRAP, with IC50 ± SEM [μg/mL] values of 9.38 ± 0.46 and 15.46 ± 0.52, respectively. The antioxidative activity-guided fractionations were performed according to the DPPH and FRAP screening results. Fourteen fractions from the 50% ethanol extract showed dissimilar antioxidative activity against DPPH and FRAP of 8.16 ± 0.76 ∼ 38.42 ± 0.58 μg/mL and 13.22 ± 0.68 ∼ 61.47 ± 0.49 μg/mL. The chemical assay-guided separation of the active fractions (fractions 3, 6, 7 and 8) led to eight phenols: protocatechuic aldehyde (1), ethyl gallate (2), rhododendrin (3), p-hydroxyacetophenone (4), rhododendrol (5), protocatechuic acid ethyl ester (6), frambinone (7) and ethylparaben (8). All phenols are reported here for the first time from S. tangutica Engl. Protocatechuic aldehyde (1), ethyl gallate (2), rhododendrin (3) and protocatechuic acid ethyl ester (6) showed strong antioxidative activities (IC50 ± SEM [mM] between 8.79 ± 0.15 and 4.25 ± 0.47 and between 6.15 ± 0.48 and 2.83 ± 0.49) against DPPH and FRAP.