The mechanism and regioselectivity of 1,3-dipolar reaction of 2-azido-N-(4-diazenylphenyl) acetamide and an alkyne have been studied in gas phase and in DMSO using the B3LYP-GD3 functional and 6-31G(d,p) basis set. The reaction followed a one-step mechanism with asynchronous TSs. The calculated global reactivity indices calculated revealed, among other things, the nucleophile character of the 2-azido-N-(4-diazenylphenyl)acetamide and the electrophile character of the alkyne (4-bromo-2-chloro-1-ethynylbenzene), in addition to an electron transfer from the 4-bromo-2-chloro-1-ethynylbenzene towards the 2-azido-N-(4-diazenylphenyl) acetamide. The calculated local reactivity indices predicted the formation of the 1,4-triazole, with the most nucleophilic nitrogen and the most electrophilic carbon favoring its formation. However, analysis of the activation energies and thermochemistry parameters showed that the 1,5 triazole is energetically favorable and more stable under thermodynamic control. Bond order analysis coupled with bond formation evolution and the solvent effect was further investigated to support and highlight the asynchronicity in bond formation and the regioselectivity of the reaction, respectively.

In the current study, the compound 4,4-dimethoxychalcone (DMC) was structurally studied and analyzed by in silico approach against M^pro to investigate its inhibitory potential. The molecular structure of the compound was confirmed by the single crystal X-ray diffraction studies. The crystal structure packing is characterized by various hydrogen bonds, C-H…π and π…π stacking. Intermolecular interactions are quantified by Hirshfeld surface analysis and the electronic structure was optimized by DFT calculations; results are in agreement with the experimental studies. Further, DMC was virtually screened against SARS-CoV-2 main protease (PDB-ID: 6LU7) using molecular docking, and molecular dynamics (MD) simulations to identify its inhibitory potential. A significant binding affinity exists between DMC and M^pro with a -6.00 kcal/mol binding energy. A MD simulation of 30ns was carried out; the results predict DMC possessing strong binding affinity and hydrogen-bonding interactions within the active site during the simulation period. Therefore, based on the results of the current investigation, it can be inferred that a DMC molecule may be able to inhibit M^pro of COVID-19.

Analysis of addent interactions with respect to the theory of electrophilicity and nucleophilicity indexes and kinetic studies shows the polar nature of [2+3] cycloaddition of (Z)-C-(m,m,p-trimethoxyphenyl)-N-(p-methylphenyl)-nitrone to (E)-3,3,3-trichloro-1-nitroprop-1-ene. However, PES exploration results do not confirm any zwitterion on the reaction paths. On the other hand, the nature of the solvent effect and the experimentally determined activation parameter values do not exclude a scenario in which one-step and stepwise processes occur simultaneously.