title: Antioxidant constituents from rhubarb: structural requirements of stilbenes for the activity and structures of two new anthraquinone glucosides.
abstract: The methanolic extracts from five kinds of rhubarb were found to show scavenging activity for DPPH radical and .O2-. Two new anthraquinone glucosides were isolated from the rhizome of Rheum undulatum L. together with two anthraquinone glucosides, a naphthalene glucoside, and 10 stilbenes. In the screening test for radical scavenging activity of rhubarb constituents, stilbenes and a naphthalene glucoside showed activity, but anthraquinones and sennosides did not. In addition, most stilbenes inhibited lipid peroxidation of erythrocyte membrane by tert-butyl hydroperoxide. Detailed examination of the scavenging effect on various related compounds suggested the following structural requirements; 1) phenolic hydroxyl groups are essential to show the activity; 2) galloyl moiety enhances the activity; 3) glucoside moiety reduces the activity; 4) dihydrostilbene derivatives maintain the scavenging activity for the DPPH radical, but they show weak activity for .O2-. In addition, several stilbenes with both the 3-hydroxyl and 4'-methoxyl groups inhibited xanthine oxidase.
authors.affiliation: Kyoto Pharmaceutical University, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Matsuda
authors.forename: T
authors.initials: T
authors.lastname: Morikawa
authors.forename: I
authors.initials: I
authors.lastname: Toguchida
authors.forename: J Y
authors.initials: JY
authors.lastname: Park
authors.forename: S
authors.initials: S
authors.lastname: Harima
authors.forename: M
authors.initials: M
authors.lastname: Yoshikawa
mesh_terms: D000818:Animals; D000880:Anthraquinones / Q000737:chemistry*; D000975:Antioxidants / Q000302:isolation & purification*; D004910:Erythrocyte Membrane / Q000737:chemistry / Q000187:drug effects; D016166:Free Radical Scavengers / Q000737:chemistry; D005960:Glucosides / Q000737:chemistry*; D015227:Lipid Peroxidation / Q000187:drug effects; D015394:Molecular Structure; D010946:Plants, Medicinal; D011817:Rabbits; D012250:Rheum / Q000737:chemistry*; D013267:Stilbenes / Q000302:isolation & purification*
chemical_list: D000880:Anthraquinones; D000975:Antioxidants; D016166:Free Radical Scavengers; D005960:Glucosides; D013267:Stilbenes