Design, Synthesis, and Evaluation of New Pyrazolines As Small Molecule Inhibitors of Acetylcholinesterase

In pursuit of identifying small molecule inhibitors of acetylcholinesterase (AChE), the synthesis of new 2-pyrazolines was performed efficiently. A modified spectrophotometric method was used to examine their inhibitory effects on AChE as well as butyrylcholinesterase. Four compounds (2a, 2g, 2j, and 2l) were identified as selective AChE inhibitors. Molecular docking studies were conducted to explore their potential interactions with the active site of AChE (PDB code: 4EY7). 1-(3-Nitrophenyl)-3-(thiophen-3-yl)-5-[4-(4-morpholinyl)phenyl]-2-pyrazoline (2l) exerted significant AChE inhibitory action with an IC₅₀ value of 0.040 μM close to donepezil (IC₅₀ = 0.021 μM). In addition to π-π interactions with Tyr341, Tyr124, and Trp86 residues, compound 2l was also capable of forming two hydrogen bonds and a salt bridge at the active site of AChE thanks to its nitro group at the meta position of the phenyl moiety linked to the N ¹ position of the pyrazoline scaffold. The higher inhibitory effect of compound 2l on AChE when compared to other compounds in this series might be explained by these additional interactions. Based on the in vitro parallel artificial membrane permeability assay, compound 2l was found to have high blood-brain barrier permeability. In vitro and in silico studies suggest that compound 2l is a potent inhibitor of AChE, which is an important target for neurodegenerative disorders, particularly Alzheimer's disease.