Synthesis and crystal structures of new mixed-ligand schiff base complexes containing N -donor heterocyclic co-ligands: Molecular docking and pharmacophore modeling studies on the main proteases of SARS-CoV-2 virus (COVID-19 disease).

Three new mixed-ligand copper(II) complexes ( 1 - 3 ) with NN'O type unsymmetrical tridentate Schiff base ligands (SB) and N -donor heterocyclic co-ligands, with general formula [Cu(SB)(L)]ClO 4 , were synthesized and characterized using single crystal x-ray diffraction (SCXRD), FT-IR and UV-Vis spectroscopy and elemental analyses. The SB ligand is the half-unit form of the condensation of 1,3-propanediamine with 5-methoxysalicylaldehyde and the co-ligands (L) are pyridine (py in (1) ), 2,2'-bipyridine (bpy in (2) ) and 1,10-phenanthroline (phen in (3) ). Crystal structures of (2) and (3) were obtained by SCXRD. Molecular docking and pharmacophore studies were performed to study the interactions between the synthesized complexes and SARS-CoV-2 virus main proteases (PDB IDs: 6LU7, 6WQF and 6W9C). Results revealed that complex (3) with phen co-ligand showed better docking scores with the three receptors, i.e. 6LU7 (-8.05 kcal.mol -1 ), 6W9C (-7.70 kcal.mol -1 ) and 6WQF (-7.75 kcal.mol -1 ). The order of the binding best energies for (3) was also as follows: 6LU7 > 6WQF > 6W9C. All of the studied complexes showed considerable performance, comparable to the standard drug, Favipiravir.