title: Flavonoids from the flower of Rhododendron yedoense var. poukhanense and their antioxidant activities.
abstract: Antioxidant flavonoids have been isolated from the flower of Rhododendron yedoense var. poukhanense. One new flavonoid and three known flavonoids, quercetin-5-O-beta-D-glucopyranoside (1), quercetin (3), and quercitrin (4), were isolated from the butanol and ethyl acetate extracts of the plant. The new flavonoid was identified as myricitrin-5-methyl ether (2). The isolation of these flavonoids from this plant, for the first time, is a valuable finding. The flavonoids were evaluated for their antioxidant activities using 1,1-diphenyl-2-picrylhydrazyl free radical (DPPH), TBARS (thiobarbituric acid reactive substance) and superoxide anion radical (O2-) in the xanthine/xanthine oxidase assay system. In the DPPH scavenging assay, the IC50 values were 4.5 +/- 0.48 microM for compound 2 and 9.7 +/- 0.29 microM for compound 3, which showed an antioxidant activity approximately 1.5-2 times higher than the antioxidant activity of alpha-tocopherol (9.8 +/- 0.94 microM). Additionally, the antioxidant activities of myricitrin-5-methyl ether (2) (IC50 = 1.7 +/- 0.22 microM) and quercetrin (4) (IC50 = 1.9 +/- 0.63 microM) were higher than that of L-ascorbic acid (IC50 = 7.4 +/- 0.63 microM) when evaluated using a TBARS assay. Compound 2 showed high activity in both the inhibition of xanthine oxidase (1.1 +/- 0.21 mM) and in the activation of superoxide scavenging.
authors: Graduate School of Biotechnology & Plant Metabolism Research Center, Kyung Hee University, Suwon 449-701, Korea.
authors: Sung Je
authors: SJ
authors: Jung
authors: Dong-Hyun
authors: DH
authors: Kim
authors: Yoon-Hee
authors: YH
authors: Hong
authors: Jin-Hee
authors: JH
authors: Lee
authors: Hyo-Nam
authors: HN
authors: Song
authors: Young-Deok
authors: YD
authors: Rho
authors: Nam-In
authors: NI
authors: Baek
mesh_terms: D001713:Biphenyl Compounds / Q000737:chemistry; D005419:Flavonoids / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D035264:Flowers / Q000737:chemistry; D016166:Free Radical Scavengers / Q000737:chemistry / Q000302:isolation & purification / Q000494:pharmacology*; D005609:Free Radicals / Q000737:chemistry*; D006834:Hydrazines / Q000737:chemistry; D015394:Molecular Structure; D010084:Oxidation-Reduction; D010851:Picrates; D029793:Rhododendron / Q000737:chemistry*; D013329:Structure-Activity Relationship; D013481:Superoxides / Q000737:chemistry; D017392:Thiobarbituric Acid Reactive Substances / Q000737:chemistry; D014969:Xanthine Oxidase / Q000737:chemistry
chemical_list: D001713:Biphenyl Compounds; D005419:Flavonoids; D016166:Free Radical Scavengers; D005609:Free Radicals; D006834:Hydrazines; D010851:Picrates; D017392:Thiobarbituric Acid Reactive Substances; D013481:Superoxides; C004931:1,1-diphenyl-2-picrylhydrazyl; D014969:Xanthine Oxidase