By bioassay-guided separation, three stilbenes (rhapontigenin, piceatannol, and resveratrol), two stilbene glucoside gallates (rhaponticin 2''-O-gallate and rhaponticin 6"-O-gallate), and a naphthalene glucoside (torachrysone 8-O-beta -D-glucopyranoside) with inhibitory activity against nitric oxide (NO) production in lipopolysaccharide-activated macrophages were isolated (IC50 = 11-69 muM). The oxygen functions (-OH, -OCH3) of stilbenes at the benzene ring were essential for the activity. The glucoside moiety reduced the activity, while the alpha,beta -double bond had no effect. Furthermore, the active stilbenes (rhapontigenin, piceatannol, and resveratrol) did not inhibit inducible NO synthase activity, but they inhibited nuclear factor-kappaB activation following expression of inducible NO synthase. (C) 2001 Elsevier Science Ltd. All rights reserved.
Effects of stilbene constituents from rhubarb on nitric oxide production in lipopolysaccharide-activated macrophages
Two new anthraquinone glucosides [chrysophanol 8-O-beta-D-(6'-galloyl)-glucopyranoside, aloe-emodin 1-O-beta-D-glucopyranoside] together with various known stilbenes and their glucosides, anthraquinone glucosides, and a naphthalene glucoside were isolated from the rhizome of Rheum undulatum L. Three stilbenes (rhapontigenin, piceatannol, resveratrol), a naphthalene glucoside (torachrysone 8-O-beta-D-glucopyranoside), and two stilbene glucoside gallates (rhaponticin 2 "-O-gallate, rhaponticin 6 "-O-gallate) showed inhibitory activity of NO production in lipopolysaccharide-activated macrophages. (IC50 = 11-69 mu M). The oxygen Functions (-OH,-OCH3) at the benzene ring were found to be essential to show the activity. Whereas, the glucoside moiety reduced the activity, while the alpha,beta-double bond did not affect the activity. Furthermore; the active stilbenes (rhapontigenin, piceatannol, resveratrol) inhibited iNOS induction. (C) 2000 Elsevier Science Ltd. All rights reserved.
Antioxidant constituents from rhubarb: structural requirements of stilbenes for the activity and structures of two new anthraquinone glucosides
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