Identification and Antioxidant Activity of Novel Chlorogenic Acid Derivatives from Bamboo (Phyllostachys edulis)

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Abstract
One known and two novel antioxidant compounds have been isolated from bamboo (Phyllostachys edulis). The butanol-soluble extract of the bamboo leaves was found to have a significant antioxidant activity, as measured by scavenging the stable 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical and the superoxide anion radical (O2-) in the xanthine/xanthine oxidase assay system. Antioxidant activity-directed fractionation of the extract led to the isolation and characterization of three structural isomeric chlorogenic acid derivatives: 3-O-(3‘-methylcaffeoyl)quinic acid (1), 5-O-caffeoyl-4-methylquinic acid (2), and 3-O-caffeoyl-1-methylquinic acid (3). Compounds 2 and 3 were isolated and characterized for the first time from the natural products. In the DPPH scavenging assay as well as in the iron-induced rat microsomal lipid peroxidation system, compounds 2 (IC50 = 8.8 and 19.2 μM) and 3 (IC50 = 6.9 and 14.6 μM) showed ∼2−4 times higher antioxidant activity than did chlorogenic acid (IC50 = 12.3 and 28.3 μM) and other related hydroxycinnamates such as caffeic acid (IC50 =13.7 and 25.5 μM) and ferulic acid (IC50 = 36.5 and 56.9 μM). Among the three compounds, compound 1 yielded the weakest antioxidant activity, and the DPPH scavenging and lipid peroxidation inhibitory activity (IC50 = 16.0 and 29.8 μM) was lower than those of chlorogenic and caffeic acids. All three compounds exhibited both superoxide scavenging activities and inhibitory effects on xanthine oxidase. Their superoxide anion (O2-) scavenging activities (IC50 = 1, 4.3 μM; 2, 2.8 μM; and 3, 1.2 μM) were markedly stronger than those of ascorbic acid (IC50 = 56.0 μM), α-tocopherol (IC50 > 100 μM), and other test compounds, although their inhibition effects on xanthine oxidase may contribute to the potent scavenging activity. α-Tocopherol exerted a significant inhibitory effect (65.5% of the control) on superoxide generation in 12-O-tetradecanoylphorbol-13-acetate-induced human promyelocytic leukemia HL-60 cells, and compound 3 showed moderate activity (36.0%). On the other hand, other compounds including 1, 2, chlorogenic acid, and other antioxidants were weakly active (24.8−10.1%) in the suppression of superoxide generation. Keywords: Chlorogenic acid derivatives; free radical scavenging; superoxide; xanthine oxidase; Phyllostachys edulis; antioxidant activity

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