Isolation and Identification of Compounds with Antioxidant Activity from Gynostemma pentaphyllum Makino
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Abstract:
Compounds with radical-scavenging and antioxidant activities were isolated from Gynostemma pentaphyllum Makino, and their antioxidant properties were studied. The compounds were purified using various column chromatography techniques, the structures of the compounds were determined mainly by proton and carbon-13 nuclear magnetic resonance (1H-NMR and 13C-NMR) spectroscopy, and the fingerprints of the compounds were analyzed by high performance liquid chromatography (HPLC). The radical-scavenging and antioxidant activities of the compounds were evaluated using the 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and ferric reducing antioxidant power (FRAP) assays. Two compounds with strong antioxidant activity were obtained from the n-butanol and ethyl acetate fractions of G. pentaphyllum and identified as kaempferol 3-O-[2G-(E)-coumaroyl-3G-O-β-D-glucosyl-(3R)-O-β-D- glucosylrutinoside] (compound 1) and 3,4-dihydroxyphenyl-O-β-D-glucopyranoside (compound 2). The presence of compounds 1 and 2 in the n-butanol and ethyl acetate fractions, respectively, was verified by HPLC fingerprinting. DPPH assays revealed that both compound 1 and compound 2 have strong radical-scavenging activity against DPPH. In the concentration range of 400~800 μg/mL, the antioxidant activity of compound 1 was stronger than that of vitamin C (Vc). ABTS assays showed that in the concentration range of 12.5~100 μg/mL, the radical-scavenging activities of compound 1 and compound 2 were stronger than that of Vc. Finally, FRAP assays indicated that the antioxidant activities of compounds 1 and 2 at low concentrations were weaker than that of Vc, but the activities of these compounds at a concentration of 800 μg/mL were comparable to that of Vc.
