Synthesis, crystal structure, biological evaluation, in silico ADME properties, enzymatic target prediction and molecular docking studies of pyrazolone-azomethine analogs

Abstract

A series of twelve azomethine analogs (3a-l) of 4-aminoantipyrine (4-AA) were prepared and characterized using FT-IR, 1HNMR and EI mass spectrometric analysis. Analog 3f was obtained as a single crystal, and X-ray diffraction (XRD) data indicated its adoption of a trans configuration around the central azomethine (CN) group, forming monoclinic P2(1)/n symmetry. The unit cell of 3f contains four molecules, and its crystal packing is stabilized through significant intermolecular host-guest CH⋯O, CH⋯π, and π⋯π interactions, resulting in a stacked supramolecular structure. In vitro bactericidal and fungicidal screening of analogs 3a-l was performed against twelve bacterial and five fungal strains, respectively. Most of the analogs demonstrated weak to moderate antimicrobial activities, specifically 3a, 3b, 3e and 3g exhibited highest activity against S. boydii, B. megaterium; S. sonnei and E. coli, respectively and 3c, 3d and 3l showed potent fungicidal activity against A. flavus, C. albicans, and N. crassa, respectively. The results indicate that the antimicrobial potency is largely dependent on the nature of the aromatic ring linked pyrazolone moiety via azomethine (CN) group. DPPH free radical scavenging assay revealed analogs 3e, 3l, 3g, 3k, 3h and 3d had IC50 values of 0.07, 1.19, 2.31, 2.57, 4.04 and 4.07 µg mL−1, respectively, comparable to that of the standard ascorbic acid (IC50 = 4.10 µg mL−1). Docking simulations were conducted to elucidate the binding mode of potent antibacterial analogs (3e and 3g) and antifungal analogs (3d and 3l) within the active sites of KAS (E. coli) and CYP 51 (C. albicans) receptors, respectively. The results revealed strong binding affinities between the studied molecules and the respective proteins. All the tested analogs fulfill the condition of Lipinski's rule of five (ROF) and Veber's rule, and the calculated ADMET profile indicated favorable drug-likeness, pharmacokinetic properties, and drug scores. Ligand-based enzymatic target predictions suggest that analogs 3a-l have potential as inhibitors of kinases, enzymes, proteases, or ligands for Family A GPCR. Finally, DFT calculations using the B3LYP/6-311G(d,p) level of theory provide insights into the FMO energies, global molecular reactivity, and biological properties of the azomethine analogs of 4-AA.