Synthesis, structure and acetylcholinesterase inhibition activity of new diarylpyrazoles

A variety of diarylpyrazole derivatives III-VI were synthesized and structurally characterized using FTIR, ¹H and ¹³C NMR spectroscopy, and in case of compound VIb by X-ray single crystal analysis. The in vitro biological studies revealed that seven of the diarylpyrazole derivatives IIIa, IIIb, IIId, IIIe, IVa, IVb and IVd are highly potent inhibitors of acetylcholinesterase enzyme with IC₅₀ values of 0.48 ± 0.092 µg/mL, 0.45 ± 0.093 µg/mL, 0.30 ± 0.014 µg/mL, 0.59 ± 0.072 µg/mL, 0.29 ± 0.084 µg/mL, 0.56 ± 0.010 µg/mL and 0.28 ± 0.096 µg/mL, respectively. All these seven products were more potent than the standard drug, donepezil (IC₅₀ = 0.73 ± 0.015 µg/mL), while compounds IIIc (0.67 ± 0.099 µg/ml) and VIa (0.66 ± 0.069 µg/ml) are almost equipotent to the donepezil. Particularly, compounds IVa and IVd are highly active acetylcholinesterase enzyme inhibitors, demonstrating more than two-fold inhibitory activity than the reference inhibitor. Molecular docking studies were carried out to identify the possible binding modes of the diarylpyrazoles within the active pocket of the enzymes. The docking interactions of the synthesized compounds with acetylcholinesterase also provided high docking scores. These results clearly indicate the potential of these compound as powerful lead molecules for further investigations.