Synthesis, Characterization, DFT Mechanistic Study, Antibacterial Activity, Molecular Modeling, and ADMET Properties of Novel Chromone-Isoxazole Hybrids

A series of novel hybrid heterocycles incorporating isoxazole rings have been successfully synthesized, characterized, and evaluated for their antibacterial responses. The synthesized compounds were obtained by a subsequent N-alkylation and 1,3-dipolar cycloaddition reactions, their structures were identified by spectroscopy techniques (1H NMR, 13C NMR and 2D HSQC), and confirmed by mass spectrometry (HRMS). The spectroscopic data also show that the 1,3-dipolar cycloaddition (1,3-DC) reactions proceed in a regiospecific manner to give only one cycloadduct. The observed regioselectivity and the mechanistic study of the 1,3-DC reaction were further highlighted and explained using Density Functional Theory (DFT) calculations with the B3LYP/6-31G(d,p) basis set and Electron Localization Function (ELF) analysis. Moreover, the antibacterial screening shows that some compounds exhibit good efficacy against the tested bacterial strains. In addition, molecular docking studies were carried out to highlight the modes of interaction between the most active molecule 5d and receptors of Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus strains. The results show that the studied compound was effectively docked to the active sites of each responsible protein with high protein-binding energies in kcal/mol. Finally, the prediction of ADMET properties suggests that almost all the hybrid compounds have good pharmacokinetic profiles, with no observed signs of toxicity, except for compounds 5e, 5f and 5g.