Natural Compounds as Inhibitors of SARS-CoV-2 Main Protease (3CLpro): A Molecular Docking and Simulation Approach to Combat COVID-19

Recently, the emergence and dissemination of SARS-CoV-2 has caused high mortality and enormous economic loss. In the fight against COVID-19, the rapid development of new drug molecules is the need of hour. However, the conventional approaches of drug development is time consuming and costly in nature. In this study, we have adopted an alternative approach to identify lead molecules from natural sources using high throughput virtual screening approach. Ligands from natural compounds library from Selleck Inc (L1400) have been screened to evaluate their ability to bind and inhibit the main protease (M^pro or 3CL^pro) of SARS-CoV-2, which is a potential drug target. We found that Kaempferol, Quercetin, and Rutin were able to bind at the substrate binding pocket of 3CL^pro with high affinity (10⁵-10⁶ M^-1) and interact with the active site residues such as His41 and Cys145 through hydrogen bonding and hydrophobic interactions. In fact, the binding affinity of Rutin was much higher than Chloroquine (1000 times) and Hydroxychloroquine (100 times) and was comparable to that of the reference drug Remdesivir, which is in clinical trials to treat COVID-19 patients. The results suggest the potential of natural compounds (flavonoids) as novel inhibitors of SARS-CoV-2 with comparable potency as that of Remdesivir.