Computational details of molecular structure, spectroscopic properties, topological studies and SARS-Cov-2 enzyme molecular docking simulation of substituted triazolo pyrimidine thione heterocycles

Investigation the molecular structure of the system requires a detailed experience in dealing with theoretical computational guides to highlight its important role. Molecular structure of three heterocyclic compounds 8,10-diphenylpyrido[3,2–e][1,2,4]triazolo[4,3–c]pyrimidine-3(2H)-thione (HL), 8-phenyl-10-(p-tolyl)pyrido[3,2–e][1,2,4]triazolo[4,3–c]pyrimidine-3(2H)-thione (CH(3)L) and10-(4-nitrophenyl)-8-phenylpyrido[3,2–e][1,2,4]triazolo[4,3–c]pyrimidine-3(2H)-thione (NO(2)L) was studied at DFT/B3LYP/6-31G (d,p) level in ethanol solvent. Spectroscopic properties such Infrared (IR, (1)H NMR and (13)C NMR) and ultraviolet–visible (UV–VIS) analyses were computed. Some quantum and reactivity parameters (HOMO energy, LUMO energy, energy gap, ionization potential, electron affinity, chemical potential, global softness, lipophelicity) were studied, also molecular electrostatic potential (MEP) was performed to indicate the reactive nucleophilic and electrophilic sites. The effects of H-, CH(3)– and NO(2)– substituents on heterocyclic ligands were studied and it was found that the electron donation sites concerned with hydrogen and methyl substituents over nitro substituent. Topological analysis using reduced density gradient (RDG) was discussed in details. To predict the relevant antiviral activity of the reported heterocyclic compounds, molecular docking simulation was applied to the crystal structure of SARS-Cov-2 viral M(pro) enzyme with 6WTT code and PL(pro) with 7JRN code. The enzymatic viral protein gives an image about the binding affinity between the target protein receptor and the heterocyclic ligands entitled. The hydrogen bonding interactions were evaluated from molecular docking with different strength for each ligand compound to discuss the efficiency of heterocyclic ligands toward viral inhibition.