Antioxidant activity of extracts from stems Alyxia reinwardtii

Abstract

In a search for antioxidant compounds from Thai medicinal plants, the dichloromethane and ethyl acetate crude extracts from the stems of Alyxia reinwardtii (chalood in Thai) showed potent antioxidant activity, as guided by scavenging effect on the stable radical, 2,2-diphenyl-1-picrylhydrazyl (DPPH). These crude extracts were isolated to afford eight compounds, namely coumarin (1), 3-hydroxycoumarin (2), 6-hydroxycoumarin (3), 8-hydroxycoumarin (4), scopoletin (5), (+)-pinoresinol (6), zhebeiresinol (7), and p-hydroxybenzoic acid (8). The structures of all compounds were characterized by means of NMR, MS, chemical analysis, and comparison with the literature data. The structure of compound 7 was also confirmed by X-ray crystallography. In terms of antioxidant activity, the isolated compounds were evaluated by various in vitro model assays, which include the DPPH radical scavenging activity, xanthine oxidase-related activity (Superoxide scavenging activity and inhibitory effect on xanthine oxidase), and lipid peroxidation inhibitory activity.The free radical scavenging activity on DPPH indicated that compound 7 (IC[subscript 50] = 0.19 mM) showed the highest activity, followed by 6 (IC[subscript 50] = 0.31 mM), 2 (IC[subscript 50] = 0.61 mM), 5 (IC[subscript 50] = 3.17 mM), and 4 (IC[subscript 50] = 71.05 mM) respectively, while compounds 1, 3, and 8 gave the weakest activity (IC[subscript 50] > 100 mM). In addition, compounds 2 (IC[subscript 50] = 4.55 mM), 6 (IC[subscript 50] = 4.51 mM), 7(IC[subscript 50] = 3.38 mM) exhibited significant superoxide scavenging activity while compound 1 and 8 were found to be inactive (IC[subscript 50] > 100 mM) However, all compounds displayed no activity on inhibitory activity against xanthine oxidase. In lipid peroxidation inhibitory activity, compounds 6 and 7 showed potent activity (IC[subscript 50] = 3.31 and 2.08 mM, respectively), while compounds 1, 2, 3, and 4 showed moderate activity (IC[subscript 50] = 67.64,69.07, 67.45, and 58.13 mM, respectively)