Synthesis, enzyme inhibitory kinetics mechanism and computational study of N-(4-methoxyphenethyl)- N-(substituted)-4-methylbenzenesulfonamides as novel therapeutic agents for Alzheimer's disease

Abstract

The present study comprises the synthesis of a new series of sulfonamides derived from 4-methoxyphenethylamine (1). The synthesis was initiated by the reaction of 1 with 4-methylbenzenesulfonyl chloride (2) in aqueous sodium carbonate solution at pH 9 to yield N-(4-methoxyphenethyl)-4-methylbenzensulfonamide (3).This parent molecule 3 was subsequently treated with various alkyl/aralkyl halides, (4a-j), using N,N-dimethylformamide (DMF) as solvent and LiH as activator to produce a series of new N-(4-methoxyphenethyl)-N-(substituted)-4-methylbenzenesulfonamides (5a-j). The structural characterization of these derivatives was carried out by spectroscopic techniques like IR, ¹H-NMR, and ¹³C-NMR. The elemental analysis data was also coherent with spectral data of these molecules. The inhibitory effects on acetylcholinesterase and DPPH were evaluated and it was observed that N-(4-Methoxyphenethyl)-4-methyl-N-(2-propyl)benzensulfonamide (5c) showed acetylcholinesterase inhibitory activity 0.075 ± 0.001 (IC₅₀ 0.075 ± 0.001 µM) comparable to Neostigmine methylsulfate (IC₅₀ 2.038 ± 0.039 µM).The docking studies of synthesized ligands 5a-j were also carried out against acetylcholinesterase (PDBID 4PQE) to compare the binding affinities with IC₅₀ values. The kinetic mechanism analyzed by Lineweaver-Burk plots demonstrated that compound (5c) inhibits the acetylcholinesterase competitively to form an enzyme inhibitor complex. The inhibition constants Ki calculated from Dixon plots for compound (5c) is 2.5 µM. It was also found from kinetic analysis that derivative 5c irreversible enzyme inhibitor complex. It is proposed on the basis of our investigation that title compound 5c may serve as lead structure for the design of more potent acetylcholinesterase inhibitors.

Keywords: Acetylcholinesterase; Alkyl/aralkyl halides; Molecular docking; Spectral analysis; Sulfonamides.

Figure 1. Structure of sulfanilamide.

Figure 2. Outline for the synthesis of different N-substituted derivatives, 5a–j, of N-(4-methoxyphenethyl)-4-methylbenzensulfonamide (3).

Reagents & Conditions: (I) Aq. Na₂CO₃ soln./pH 9–10/stirring at RT for 2–3 h. (II) DMF/LiH/stirring at RT for 0.5 h for activation/then addition of R-X (4a–j) and stirring finally for 4–5 h.

Figure 3. Lineweaver–Burk plots.

Lineweaver–Burk plots for inhibition of acetylcholine esterase from human erythrocytes in the presence of Compound 5c (A). Concentrations of 5c were 0.00, 0.075 and 0.15 µM; substrate acetylthiocholine iodide concentrations were 4, 2, 1, 0.5, 0.25, and 0.125 mM. (B) The inset represents the plot of the slope.

Figure 4. Human acetylcholinesterase and Ramachandran graph.

(A) Protein structure of human acetylcholinesterase; (B) Ramachandran graph of target protein.

Figure 5. Docking energy.

Docking energy values of all synthesized docked complexes.

Figure 6. Binding pocket of target protein.

(A) Binding pocket of target protein (B) Closer view of ligands structure inside the receptor molecule.

Figure 7. Molecular docking interaction of 5c with acetylcholinesterase.

(A) The general overview of docking depiction. The protein structure is represented in green color in surface format while ligand is highlighted in grey color. (B) The closer view of binding pocket interaction with best conformation position of ligand against target protein. The ligand molecule is depicted in grey color while their functional groups such as oxygen, amino and sulfur are showed in red, blue and yellow colors, respectively. (C) The docking complex is represented with ligand conformation. Amino acids are highlighted in dark brown color, while protein structure is represented in green and pink colors, respectively. (D) The closer view of docking complex. The residues involved in the interaction pattern are highlighted in maroon. Light blue dotted lines with distance mentioned in angstrom (Å) are justified for hydrophobic interactions.