title: Antibacterial and antioxidant activities of quercetin oxidation products from yellow onion (Allium cepa) skin.
abstract: Four new quercetin-derived oxidation products (1-4) and lunularin-4-O-beta-D-glucoside (5) were isolated from a water extract of onion (Allium cepa) skin, together with 17 other known compounds. Antibacterial assays for the isolated compounds showed that 2-(3,4-dihydroxyphenyl)-4,6-dihydroxy-2-methoxybenzofuran-3-one (1) presented selective activity against Helicobacter pylori strains and 3-(quercetin-8-yl)-2,3-epoxyflavanone (4) showed antibacterial activity against MRSA and H. pylori strains at the same time that it increased susceptibility of MRSA to beta-lactams. Evaluation of antioxidant activity against DPPH for the isolated compounds showed that the new derivative compounds (1-4) and 2,5,7,3',4'-pentahydroxy-3,4-flavandione (6) are more active than quercetin.
authors.affiliation: Graduate School of Pharmaceutical Sciences, University of Tokushima, Shomachi-l-78-1, Tokushima 770-8505, Japan.
authors.forename: Freddy A
authors.initials: FA
authors.lastname: Ramos
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Takaishi
authors.forename: Miki
authors.initials: M
authors.lastname: Shirotori
authors.forename: Yousuke
authors.initials: Y
authors.lastname: Kawaguchi
authors.forename: Koichiro
authors.initials: K
authors.lastname: Tsuchiya
authors.forename: Hirofumi
authors.initials: H
authors.lastname: Shibata
authors.forename: Tomihiko
authors.initials: T
authors.lastname: Higuti
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Tadokoro
authors.forename: Minoru
authors.initials: M
authors.lastname: Takeuchi
mesh_terms: D000900:Anti-Bacterial Agents / Q000302:isolation & purification / Q000494:pharmacology*; D000975:Antioxidants / Q000302:isolation & purification / Q000494:pharmacology*; D001632:Bibenzyls / Q000737:chemistry / Q000302:isolation & purification; D001713:Biphenyl Compounds; D052978:Disk Diffusion Antimicrobial Tests; D005960:Glucosides / Q000737:chemistry / Q000302:isolation & purification; D016480:Helicobacter pylori / Q000187:drug effects; D006834:Hydrazines; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects; D015394:Molecular Structure; D019697:Onions / Q000737:chemistry*; D010636:Phenols / Q000737:chemistry / Q000302:isolation & purification; D010851:Picrates; D010936:Plant Extracts / Q000302:isolation & purification
chemical_list: D000900:Anti-Bacterial Agents; D000975:Antioxidants; D001632:Bibenzyls; D001713:Biphenyl Compounds; D005960:Glucosides; D006834:Hydrazines; D010636:Phenols; D010851:Picrates; D010936:Plant Extracts; C534852:lunularin-4-O-beta-D-glucoside; C004931:1,1-diphenyl-2-picrylhydrazyl