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Emergence of COVID-19 and thereafter intensive research on bioactive natural compounds against SARS-CoV-2, identified a large number of phytochemicals (i.e., plants-derived) and mycochemicals (i.e., fungi-derived) as potential inhibitors with proven antiviral properties against SARS-CoV-2, but there are no comparative study on the reported compounds. A comparative study among the previously identified/reported main protease (Mpro) inhibitors of SARS-CoV-2 can lead to the most potent compound that eventually helps to make an effective drug lead against SARS-CoV-2. Through manual literature curation, we selected 57 potential bioactive compounds and screened them against Mpro protein of SARS-CoV-2. A series of in silico screening such as binding affinity, drug-like properties, pharmacokinetic, physicochemical, and ADMET studies identified top ten compounds as potential Mpro inhibitors. Further, docking studies prioritized the top two compounds namely Norquinadoline A and Quinadoline B, based on their predicted affinity for the target protein. Binding free energy calculations further emphasized them as top candidates for effective Mpro inhibitors that hold promise for drug development against COVID-19. In-depth molecular dynamics studies and MM/PBSA analysis culminated in the recognition of Norquinadoline A as the most potent Mpro inhibitor of SARS-CoV-2. Thus, Norquinadoline A can be used as lead compound in further drug discovery process after in vitro and in vivo experimental studies.