Are Plant-derived Flavonoids the Emerging Anti-coronavirus Agents?

The current outbreak of coronavirus disease 2019 (COVID-19), which is an infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has negatively impacted the global health and economy. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) shares many similarities with SARS-CoV and Middle East respiratory syndrome-related coronavirus. It has been identified that the 3C-like protease (3CLpro) enzyme in coronaviruses can be a major therapeutic target for combating these serious infections. Therefore, flavonoids are believed to hold high potential in eliminating the viruses and infections. Flavonoids are polyphenolic secondary metabolites found in plants and have been demonstrated for their notable benefits for health. The antiviral activity of flavonoids has been reported in recent studies. Flavonoids, such as apigenin, quercetin, luteolin, amentoflavone, epigallocatechin gallate, gallocatechin gallate, and kaempferol, are known to be able to fight against coronaviruses by reducing the 3CLpro activity, according to the docking studies. Besides, we also found that several flavonoids have the potential to suppress the inflammatory cytokines, which are generally expressed in the lungs of coronavirus-infected individuals. However, the studies utilizing 3CLpro using various scaffolds of flavonoids need to be performed for better understanding on the antiviral potential of flavonoid derivatives against 3CLpro.