Synthesis, structural characterization, and biological evaluation of cinnamaldehyde–azomethine hybrids: In Vitro and In Silico approaches

We herein reported the synthesis and investigation of biologically active novel compounds, which integrate cinnamaldehydes and azomethine moieties into one molecule. Seven cinnamaldehyde-based azomethines with polyamine backbones were synthesized by condensation reaction in a non-catalyst medium, and their structures were studied by NMR, FTIR, mass and elemental analysis. Antibacterial activity was investigated against Gram-positive and Gram-negative bacterial strains by a two-fold microdilution method, and results were compared with the known antibiotics. The obtained results revealed that compound 5 exhibited promising activity against a clinical isolate of S. aureus, with a MIC value of 0.016 μmol/mL (8 μg/mL); therefore, due to its lowest MIC, the time-kill kinetics and growth inhibitory effects were further evaluated at 2× MIC to assess its bactericidal potential. Cytotoxicity studies demonstrated that compound 5 exhibited minimal toxicity toward human keratinocyte cells, indicating low overall cytotoxicity on mammalian cells. To study the mechanism of action of compound 5, the effect of the investigated molecule on the ultrastructural organization of S. aureus was studied by using transmission electron microscopy, which showed that the investigated sample directly affects the process of bacterial replication by revealing nucleoid enlightenment, remnants of destructively altered fragments of the cell septum, disruption of cell wall structure. To elucidate the antibacterial mechanism of the targeted compound, molecular docking identified target proteins 3VSL and 5M18 with their catalytic and allosteric sites, and 100 ns MD simulations (RMSD, Rg, SASA, RMSF) confirmed the synthesized ligand's stable binding and interaction with these proteins.