The potential of 39 antiviral flavonoids for inhibition of the main protease of coronavirus disease 2019 (COVID-19) was investigated using a molecular docking approach. The studied flavonoids were protease inhibitors of human immunodeficiency viruses (HIV), severe acute respiratory syndrome (SARS), hepatitis C virus (HCV), or Ebola virus. Both affinity and similarity-based molecular docking approach was applied to improve the reliability of the proposition. The estimated binding energy proposed six flavonoids for COVID-19 therapy. Then the similarity-based molecular docking arranged the candidate flavonoids respectively as Quercetin 3-O-(2¢¢-galloyl)-R-Larabinopyranoside from Acer okamotoanum, Tomentin D and Tomentin A from Paulownia tomentosa, Corylifol A and psoralidin from Psoralea and Ladanein from Lamiaceae. The values of similarity score for these phytochemicals respectively were-340, -225, -221, -213, -176, and -152 while the estimated binding energy were -9.52, -7.74, -7.67, -8.09, -8.58, and -8.02 (kcal mol-1). Also, ligand map probing of native and six flavonoids was shown Phe 140, Gly 143, His 164, Glu 166, Gln 189, Thr 190, Thr 26, Cys 145, and Asn 142 amino acids of the active site of main protease of Covid-19 commonly was in the hydrogen or steric interactions with these inhibitors. This study outstanding the inhibitor effect of some antiviral non-nutrient plant compounds against the main protease of COVID-19.
