Synthesis, design, and cholinesterase inhibitory activity of novel 1,2,4-triazole Schiff bases: A combined...

Alzheimer's disease (AD), a progressive neurodegenerative disorder, is characterized by cholinergic dysfunction, necessitating the development of potent cholinesterase inhibitors for therapeutic intervention. In this research, a series of novel 1,2,4-triazole Schiff bases (S1-S8) was successfully synthesized and tested for their cholinesterase inhibitory activities both in vitro and in silico. 4-Hydroxy-3-methoxybenzaldehyde reacted with 4-methylbenzene sulfonyl chloride, then refluxed and recrystallized to form 4-formyl-2-methoxyphenyl 4-methyl benzenesulfonate, which combined with 4-amino-5-alkyl(aryl)-2,4-dihydro-3H-1,2,4-triazol-3-ones in acetic acid to yield Schiff bases. The synthesis yielded high-purity compounds with efficiency ranging from 87.5 % to 99.5 %, confirmed through IR, ¹H NMR, ¹³C NMR, and UV-Vis spectroscopy. The biological evaluation showed that S4 demonstrated the strongest inhibition of acetylcholinesterase (AChE) with an IC₅₀ of 3.00 μM, significantly outperforming rivastigmine (IC₅₀ = 8.95 μM) and galantamine (IC₅₀ = 29.5 μM). Additionally, S7 emerged as the most effective inhibitor of butyrylcholinesterase (BChE), with an IC₅₀ of 0.77 μM, comparable to rivastigmine (IC₅₀ = 0.62 μM) and far stronger than galantamine (IC₅₀ = 27.8 μM). The K_i values reinforced the selective inhibition properties, with S4 (1.04 ± 0.003 μM) and S7 (0.61 ± 0.001 μM) showing high affinity for AChE and BChE, respectively. Molecular docking studies identified crucial π-π interactions and hydrogen bonding between the triazole derivatives and key enzyme residues, contributing to their high inhibitory potency. These interactions were further validated through molecular dynamics simulations, which confirmed the stability of the S4 and S7 complexes with AChE and BChE over extended periods. Computational analysis, including FMO studies, supported the experimental data, showing that HOMO-LUMO energy gaps significantly influenced the compounds' reactivity, stability, and inhibitory profiles. Overall, the study presents strong evidence that these novel 1,2,4-triazole Schiff bases possess potent and selective cholinesterase inhibition, notably S4 for AChE and S7 for BChE. These results suggest that these novel compounds have significant potential as selective cholinesterase inhibitors, particularly for Alzheimer's disease, warranting further in vivo studies.