The Glide and Induced-fit docking modules of the Maestro 12.6.144 software (Schrodinger, LLC, New York, NY, USA) were used to perform the molecular docking studies. Ligprep (Schrodinger, LLC) 55 was employed to optimize the energy of all compounds. The holo-closed P-loop conformation of Pl-pro (PDB ID: 7JRN) and the apo-opened P-loop conformation (PDB ID: 6WUU) were prepared for docking using the 'protein preparation wizard' in Maestro (Schrodinger, LLC). Bond orders and formal charges were added to hetero groups and hydrogens were added to all atoms. Side chains not close to the binding cavity and not participating in salt bridges were neutralized to avoid interference with binding interaction energy, and termini were capped with N-acetyl (ACE) and N-methyl amide (NMA) groups. The OPLSe force field was used to refine the structure and optimize the hydrogen bond network. Docking was carried out using the standard precision (SP) mode on the protein structure grid, and the Glide score was used to evaluate the final binding pose of protein-ligand complexes.