Abstract: Received: 24 May 2020 Revised: 5 September 2020 Accepted: 13 September 2020 DOI: 10.1002/ptr.6887 REVIEW A role for quercetin in coronavirus disease 2019 (COVID-19) Giuseppe Derosa1,2 | Pamela Maffioli1 | 1 Department of Internal Medicine and Therapeutics, University of Pavia, Pavia, Italy 2 Laboratory of Molecular Medicine, University of Pavia, Pavia, Italy 3 Velleja Research S.r.l., Milan, Italy Correspondence Giuseppe Derosa, Department of Internal Medicine and Therapeutics, University of Pavia, Via Aselli, 43/45, 27100 Pavia, Italy. Email: giuseppe.derosa@unipv.it Angela D'Angelo2 | Francesco Di Pierro3 Several months ago, an outbreak of pneumonia of unknown aetiology was detected in Wuhan City (China) and the aetiological agent of the atypical pneumonia was isolated by the Chinese authorities as novel coronavirus (2019-nCoV or SARS-CoV-2). The WHO announced this new disease was to be known as “COVID-19.” When looking for new antiviral compounds, knowledge of the main viral proteins is fundamental. The major druggable targets of SARS-CoV-2 include 3-chymotrypsin-like protease (3CLpro), papain-like protease (PLpro), RNA-dependent RNA polymerase, and spike (S) protein. Quercetin inhibits 3CLpro and PLpro with a docking binding energy corresponding to −6.25 and −4.62 kcal/mol, respectively. Quercetin has a theoretical, but significant, capability to interfere with SARS-CoV-2 replication, with the results showing this to be the fifth best compound out of 18 candidates. On the basis of the clinical COVID-19 manifestations, the multifaceted aspect of quercetin as both antiinflammatory and thrombin-inhibitory actions, should be taken into consideration. KEYWORDS COVID-19, infectious diseases, nutraceutical, quercetin, SARS-CoV-2 1 | I N T RO DU CT I O N appeared in Europe. The virus was isolated in Bavaria (Germany) from a German patient infected by an individual from Shanghai (China). Viral diseases continue to pose a serious threat to public health. The Subsequently, the virus was present in Italy on January 25, 2020. The world has witnessed several viral epidemics over the past 20 years, unsuspecting individuals infected with the virus are thought to have including severe acute respiratory syndrome (SARS) coronavirus been able to circulate in the area of Basso Lodigiano with few symp- (SARS-CoV-1) in 2003, the influenza disease called H1N1 in 2009, toms or with symptoms mistaken for those of influenza. and the middle east respiratory syndrome (MERS) coronavirus (MERS- On January 30, 2020, the WHO declared the situation a public CoV) in 2012. Several months ago, an outbreak of pneumonia of health unknown aetiology was detected in Wuhan City, Province of Hubei Organization, 2020a) and on February 11, 2020, the WHO announced emergency of international concern (World Health (China) and reported to the China Country Office of the World Health that the disease caused by this new virus was to be known as Organization (WHO) on December 31, 2019. The National Health “COVID-19,” which is an acronym of “coronavirus disease-2019.” Commission of China reported the outbreak was associated with On February 20, 2020, the first symptomatic COVID-19 patient exposure in one seafood market in Wuhan City. The aetiological agent was identified in Italy at the Emergency Department of Codogno Hos- of the atypical pneumonia was isolated on January 7, 2020 by the pital, Basso Lodigiano, Province of..