Synthesis, X-ray structural characterization, antimicrobial screening, molecular docking, and molecular dynamics simulations of symmetrical and asymmetrical azines

A convenient, environmentally benign, and efficient one-pot protocol has been developed for the synthesis of both symmetrical and asymmetrical ketazines and aldazines via the condensation of ketones and/or aldehydes with phosphonic dihydrazide in refluxing ethanol. The approach operates under mild conditions, affords good to excellent yields, and tolerates a wide range of aromatic and heteroaromatic substrates. Structural elucidation of the synthesized azines was accomplished using 1H and 13C NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction for selected derivatives, confirming their geometric configurations and molecular conformations. A series of thirty azine derivatives was evaluated for antimicrobial activity against Gram-positive and Gram-negative bacteria, as well as yeast and filamentous fungi. Numerous compounds demonstrated selective activity against Staphylococcus aureus, while limited activity was observed against Gram-negative strains. The minimum inhibitory concentration (MIC) values were generally in the range of 200–500 µg/mL, indicating a modest antimicrobial potency. The results provide insight into the structure–activity relationships of azine derivatives and highlight the influence of aromatic substitution patterns on biological activity. This study investigated compound 5e against Staphylococcus aureus dihydrofolate reductase (DHFR) using molecular docking, 60 ns MD simulations, and MM/GBSA binding free energy calculations. The DHFR-5e complex demonstrated superior stability (RMSD: 1.00 ± 0.14 Å) compared to the apo system, with favorable binding free energy (ΔGbind = -23.53 ± 0.27 kcal/mol) driven primarily by van der Waals interactions. Compound 5e represents a promising lead for anti-MRSA drug development. Overall, this study presents an operationally simple and versatile synthetic approach to azines, accompanied by a preliminary assessment of their antimicrobial potential.