Antioxidant Activity of Constituents from the Methanolic Extract of Acacia confusa Leaves

Abstract

In this study, the antioxidant activities of the leaf extract of Acacia confusa and constituents isolated from its ethyl acetate (EtOAc) fraction were investigated for the first time using various in vitro assays. Ten antioxidant compounds, namely, 3,4,5-trihydroxybenzoic acid methyl ester (1), 5,7,3',4'-tetrahydroxyl-flavone (2), myricetin 3-O-(3”-O-galloyl)-α-rhamnopyranoside (3), myricetin 3-O-(3”-O-galloyl)-α-rhamnopyranoside 7-methyl ether (4), myricetin 3-O-(2”-O-galloyl)-α-rhamnopyranoside 7-methyl ether (5), myricetin-3-O-β-glucopyranoside (6), myricetin-3-O-α-rhamnopyranoside (7), myricetin 3-O-(2”-O-galloyl)-α-rhamnopyranoside (8), quercetin-3-O-α-rhamnopyranoside (9), and europetin-3-O-α-rhamnopyranoside (10) were isolated and identified from the leaf extract. In addition, their 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging activity, superoxide radical-scavenging activity, and trolox equivalent antioxidant capacity (TEAC) were compared with catechin (as the positive control). As to the DPPH-scavenging activity, all compounds except for 1 and 2 displayed greater antioxidant capacities than catechin (EC50=10.3 μM), and all of their TEAC values were higher than that of catechin (3.49 mM of trolox) except for 1, 6, 9, and 10. In addition, all compounds except for 1, 2, 5, and 6, also expressed as high a superoxide radical scavenging activity as catechin (EC50=7.4 μM).