Methyl β-D-galactopyranoside esters as potential inhibitors for SARS-CoV-2 protease enzyme: synthesis, antimicrobial, PASS, molecular docking, molecular dynamics simulations and quantum computations.

Carbohydrate esters are significant in medicinal chemistry because of their efficacy for the synthesis of biologically active drugs. In the present study, methyl β-D-galactopyranoside (MGP) was treated with various acyl halides to produce 6-O-acyl MGP esters by direct acylation method with an excellent yield. To obtain newer products for antimicrobial assessment studies, the 6-O-MGP esters were further modified into 2,3,4-tri-O-acyl MGP esters containing a wide variety of functionalities in a single molecular framework. The chemical structures of the newly synthesized compounds were elucidated by analyzing their physicochemical, elemental, and spectroscopic data. In vitro antimicrobial testing against five bacteria and two fungi and the prediction of activity spectra for substances (PASS) revealed that these MGP estes have promising antifungal functionality compared to their antibacterial activities. The antimicrobial tests demonstrated that the compounds 3 and 10 were the most potent against Bacillus subtilis and Escherichia coli strains, with the minimum inhibitory concentration (MIC) values ranging from 0.352 ± 0.02 to 0.703 ± 0.01 mg/ml and minimum bactericidal concentration (MBC) values ranging from 0.704 ± 0.02 to 1.408 ± 0.04 mg/ml. Density functional theory (DFT) at the B3LYP/3-21G level of theory was employed to enumerate, frontier orbital energy, enthalpy, free energy, electronic energy, MEP, dipole moment which evaluated the effect of certain groups (aliphatic and aromatic) on drug properties. They discovered that all esters were more thermodynamically stable than the parent molecule. Molecular docking is performed using AutoDock Vina to determine the binding affinities and interactions between the MGP esters and the SARS-CoV-2 main protease. The modified esters strongly interact with the prime Cys145, His41, MET165, GLY143, THR26, and ASN142 residues. The MGP esters' shape and ability to form multiple electrostatic and hydrogen bonds with the active site match other minor-groove binders' binding modes. The molecular dynamics simulation validates the molecular docking results. The pharmacokinetic characterization of the optimized inhibitor demonstrates that these MGP esters appear to be safer inhibitors and a combination of in silico ADMET (absorption, distribution, metabolism, excretion, and toxicity) prediction and drug-likeness had promising results due to their improved kinetic properties. Structure activity relationships (SAR) study including in vitro and silico results revealed that the acyl chain, palmitoyl (C16) and 4-chlorobenzoyl (4.ClC