Abstract: Lysimachia christinae Hance(LCH) was extracted with methanol:chloroform(2:1) in a ultrasonator, and the extraction was then partitioned with petroleum ether, EtOAc and BuOH successively. Free radical scavenging activity (FRSA) of the extractions was evaluated by using DPPH radical scavenging assay, the 1,10-phenanthroline-Fe2+ oxidative and the AP-TEMED assays, and compared with that of BHT. The EAF (ethyl acetate-soluble fraction) exhibited the highest FRSA, which was greater than that of BHT. Furthermore, bioactivity-guided chromatographic fractionation was conducted by repeated column chromatography over a silica gel, RP-18, and Sephadex LH-20 to obtain three pure antiradical compounds. Their structures were determined by interpretation of the 1D and 2D NMR, as well as mass spectral data. The result demonstrated that quercetin, quercetin 3-O-β-D-glucopyranoside, and kaempferol 3-O-β-D-glucopyranoside were the major antiradical constituents in LCH.The FRSA of the compounds decreased in the following order: quercetin>quercetin 3-O-β-D-glucopyranosid>kaempferol 3-O-β-D-glucopyranoside>EAF>BHT. The FRSA of phenolic compounds is correlated to their chemical structures. In general, the FRSA of phenolics depends mainly on the number of hydrogen-donating hydroxyl groups on the aromatic ring of the phenolic molecules.

Key words: natural antioxidant, Lysimachia christinae Hance, free radical scavenging activity, antiradical constituent