Quercetin

Quercetin (C15H10O7) is a flavonoid found in fruits. It is a polyphenol with anti-carcinogenic, anti-inflammatory and antiviral activities. Quercetin may inhibit lipid peroxidation, platelet aggregation and capillary permeability. Quercetin has biological properties that suggest it may improve mental or physical performance and reduce infection risk. The name quercetin, used since 1857, derives from quercetum for oak forest, after the genus Quercus (oak). Quercetin is a polar auxin transport inhibitor. The Union of Pure and Applied Chemistry (IUPAC) nomenclature for quercetin is 3, 3′, 4′, 5, 7-pentahydroxyflvanone (or its synonym 3, 3′, 4′, 5, 7-pentahydroxy-2-phenylchromen-4-one). There is an OH group attached at positions 3, 5, 7, 3′, and 4′.

Quercetin is an aglycone lacking an attached sugar. It is a citron yellow needle crystal soluble in alcohol and lipids, insoluble in cold water and poorly soluble in hot water. Water solubility is higher for quercin glycoside. While quercetin describes the aglycone form only, the term quercetin is occasionally used to refer to quercetin-type molecules such as glycosides in the research and supplement industry. Quercetin-type flavonols, primarily found as quercetin glycosides, are the most abundant of the flavonoid molecules. They are found in a variety of fruits, vegetables, seeds, nuts, flowers, barks and leaves. Medical botanicals such as Ginko biloba, Hypericum perforatum and Sambucus canadensis contain quercetin.

The glycosylated form of quercetin, quercetin 3-β-O-d-glucoside (Q3G), was tested for antiviral activity at the Clinical Research Institute of Montreal (IRCM) by Canadian scientist, Michel Chrétien and Congolese scientist, Majambu Mbikay. The scientists collaborated with the National Microbiology Laboratory in Winnipeg for testing in mice infected with Ebola that showed quercetin to be effective. Q3G was shown to inhibit viral entry. The team also showed effectiveness of the quercetin derivative against Zika virus in mice. Chrétien and Mbikay are working with Quercegen Pharmaceuticals to produce quercetin in an oral tablet to test against COVID-19. Chrétien's team is conducting clinical trials in China with about 1000 test pateints. Quercin is U.S. Food and Drug Administration approved as safe for human consumption. Michel Chrétien is the brother of Jean Chrétien, former prime minister of Canada. Quercetin derivatives (7-O-arylmethylquercetin) have shown antiviral activity against the SARs-associated coronavirus (SARs-CoV) and the hepatitis C virus.