The phenolic constituent and free radical scavenging activities of Gynura formosona Kiamnra

Gynura formosana Kiamnra (Compositae) is a herbal folk medicine that is a popular vegetable in Taiwan. The free-radical scavenging activities of a 70% aqueous acetone extract from the herb G formosana were evaluated. Bioassay-guided fractionation, column separation on Diaion, Toyopearl HW 40(C), Sephadex LH-20 and MCI CHP20P, and high-performance liquid chromatography (HPLC) were used to isolate for the first time in G formosana four potent phenolics [caffeic acid (I), quercetin 3-O-rutinoside (II), kaempferol 3-O-rutinoside (III) and kaempferol 3-O-robinobioside (IV)]. The IC₅₀ values of 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity for compounds I-IV were 6.7, 7.7, 300.3 and 286.7 μM, respectively, and, for superoxide radical scavenging activity, they were 187.3, 25.8, 55.3 and 87.4 μM, respectively. Using a spin trapping electron spin resonance (ESR) method, caffeic acid (I) and quercetin 3-O-rutinoside (II) exhibited good hydroxyl radical activity. The free radical scavenging activity of G formosana phenolics may improve the economic value of this herb and assist in its development as a health food.