title: Antioxidant flavonoids from leaves of Polygonum hydropiper L.
abstract: Ten flavonoid compounds were isolated from the dried leaves of Polygonum hydropiper L. (Laksa leaves), and identified as 3-O-alpha-L-rhamnopyranosyloxy-3',4',5,7-tetrahydroxyflavone; 3-O-beta-D-glucopyranosyloxy-4',5,7-trihydroxyflavone; 6-hydroxyapigenin; 6"-O-(3,4,5-trihydroxybenzoyl) 3-O-beta-D-glucopyranosyloxy-3', 4', 5, 7-tetrahydroxyflavone; scutillarein; 6-hydroxyluteolin; 3',4',5,6,7-pentahydroxyflavone; 6-hydroxyluteolin-7-O-beta-D-glucopyranoside; quercetin 3-O-beta-D-glucuronide; 2"-O-(3,4,5-trihydroxybenzoyl) quercitrin; quercetin. Evaluation of the antioxidative activity, conducted in vitro, by using electron spin resonance (ESR) and ultraviolet visible (UV-vis) spectrophotometric assays, showed that these isolated flavonoids possess strong antioxidative capabilities. Measurement of the Trolox equivalent antioxidant capacity (TEAC) values, against ABTS (2,2'-azinobis(3-ethyl-benzo-thiazoline-6-sulphonic acid) radicals and phenyl-tert-butyl nitrone (PBN) azo initiator (AI) also showed strong anti-oxidative activity. The most powerful of the antioxidants was 2"-O-(3,4,5-trihydroxybenzoyl) quercitrin (galloyl quercitrin). A combination of two flavonoid compounds was tested for synergistic anti-oxidative capacity, but no significant improvement was observed.
authors.affiliation: National Institute of Education, Nanyang Technological University, 1 Nanyang Walk, Singapore 637616, Singapore.
authors.forename: Zhao Feng
authors.initials: ZF
authors.lastname: Peng
authors.forename: Dieter
authors.initials: D
authors.lastname: Strack
authors.forename: Alfred
authors.initials: A
authors.lastname: Baumert
authors.forename: Ramanathan
authors.initials: R
authors.lastname: Subramaniam
authors.forename: Ngoh Khang
authors.initials: NK
authors.lastname: Goh
authors.forename: Tet Fatt
authors.initials: TF
authors.lastname: Chia
authors.forename: Swee Ngin
authors.initials: SN
authors.lastname: Tan
authors.forename: Lian Sai
authors.initials: LS
authors.lastname: Chia
mesh_terms: D000975:Antioxidants / Q000737:chemistry* / Q000302:isolation & purification*; D004357:Drug Synergism; D005419:Flavonoids / Q000737:chemistry* / Q000302:isolation & purification*; D015394:Molecular Structure; D018515:Plant Leaves / Q000737:chemistry*; D028502:Polygonum / Q000737:chemistry*; D013997:Time Factors
chemical_list: D000975:Antioxidants; D005419:Flavonoids