We have studied the inhibitory effect of five polyphenols namely, resveratrol, piceatannol, quercetin, quercetrin, and quercetin-3-beta-D glucoside on Escherichia coli ATP synthase. Recently published X-ray crystal structures of bovine mitochondrial ATP synthase inhibited by resveratrol, piceatannol, and quercetin, suggest that these compounds bind in a hydrophobic pocket between the gamma-subu...

Externally added quercetin (100 micromolar) was oxidized by intact spinach chloroplasts at a rate of 30 micromoles per mg chlorophyll per hour in the presence of 100 micromolar H(2)O(2). The oxidation rate was increased by about 20% in a hypotonic reaction mixture. The thylakoid fraction also oxidized the flavonol in the presence of H(2)O(2), and the rate was about 25% of that by intact chlorop...

The natural flavonoid quercetin is known to activate the transcription factor Nrf2, which regulates the expression of cytoprotective enzymes such as heme oxygenase-1 (HO-1) and NAD(P)H:quinone oxidoreductase 1 (NQO1). In this study, a novel semisynthetic flavonoid 7-O-galloylquercetin (or quercetin-7-gallate, 3) was prepared by direct galloylation of quercetin, and its effect on the Nrf2 pathwa...

1,1-Dipehnyl-2-picrylhydrazyl (DPPH) radical scavenging activities were found in the extract of dried leaves of oregano (Origanum vulgare). The water-soluble active ingredients were isolated, and their structures were determined to be 4'-O-beta-D-glucopyranosyl-3',4'-dihydroxybenzyl protocatechuate and 4'-O-beta-D-glucopyranosyl-3',4'-dihydroxybenzyl 4-O-methylprotocatechuate by (1)H-, (13)C-NM...

UDP-glucuronosyltransferase (UGT) activity toward the flavonoid quercetin and UGT protein were characterized in three equidistant small intestine (SI) segments from 4-, 12-, 18-, and 28-month-old male Fischer 344 rats (n = 8/age) using villin to control for enterocyte content. SI microsomal intrinsic clearance of quercetin was increased 3- to 9-fold from 4 months in the proximal and distal SI a...

Five flavonoid glycosides were isolated from the n-butanol soluble fraction of the ethanolic extract of Rapistrum rugosum and their structures were assigned from (1)H- and (13)C-NMR spectra (DEPT) with 2D NMR as quercetin-3-O-α-L-rhamnopyranoside (1), quercetin-3-O- β-D-xyloside (2), quercetin, 3-O-α-L-arabinopyranoside,7-O-α-L-rhamnopyranoside (3), kaempferol 3-O-α-L-arabinopyranoside, 7-O-α-L...

A tannin, EA (1), and other nine non-tannins compounds, gallic acid (2), quercetin (3), myricetin (4), 3-O-methylellagic acid-4?-O-?-L-rhamnopyranoside (5), quercetin-3-O-?-D-galactopyranoside (6), kaempferol-3-O-?-D-glucoside (7), quercetin-3-O-?-D-glucuronide (8), quercetin-3-O-rutinoside (9), 3,3?,4-tri-O-methylellagic acid-4?-O-?-D-glucopyranosyl (10) were isolated from a valuable medicinal...

Quercetin, a ubiquitous flavonol, represents a promising leading drug for development of new chemotherapeutic agents. However, its limited cytotoxicity to cancer cells hampers its clinical use. In order to obtain novel quercetin derivatives with superior cytotoxicity, seven alkylated quercetin derivatives were synthesized. Solubility of these derivatives was determined by turbidimetry. Cytotoxi...

The aim of this research was to perform a phytochemical study of the methanol leaves extract of T. guianensis (MET) guided by vasodilatory and antioxidant activities. The chemical profile of MET and the ethyl acetate fraction (EA fraction) was determined by HPLC-UV-MS and EA fraction guided fractionation by reverse-phase chromatography. The vasorelaxant effects of MET, fractions, sub-fractions ...