Synthesis, in vitro, and in silico studies of 4-chlorophenyl-sulfonyl Indole based thiosemicarbazones as competitive α-glucosidase inhibitors

Abstract

The urgent need for effective and novel solutions to address the rising global epidemic of diabetes mellitus (DM) has become a priority for researchers. This chronic ailment, with its alarming prevalence and life-threatening complications (neuropathy, retinopathy and nephropathy), necessitates novel therapeutic strategies. Herein we have synthesized a novel series of N-substituted indole-based thiosemicarbazone derivatives 5(a-y) and explored their potential as α-glucosidase inhibitors. All the compounds displayed excellent inhibitory potential with IC₅₀ values in the range 5.38-59.20 µM, vastly outperforming the reference inhibitor acarbose (IC₅₀ = 871.40 ± 1.24 µM). Molecular docking and molecular dynamics simulation were also conducted, which revealed strong binding interactions with the active site of the enzyme. Compound 5u emerged as the most effective α-glucosidase inhibitor, making it a strong lead for the development of novel antidiabetic therapeutics. To strengthen the SAR rationale and to gain mechanistic insights into the enhanced α-glucosidase inhibition, quantum chemical descriptors of the eight most active thiosemicarbazones (5a, 5 h, 5 m, 5n, 5s, 5t, 5u, 5w) were computed using DFT, highlighting their reactivity and stability from a theoretical perspective.

Keywords: 4-chlorophenyl-sulfonyl indole; Glucosidase; In silico; Kinetics; Molecular docking.

Fig. 1

Reported structures of α-glucosidase inhibitors based on indole and thiosemicarbazone, along with their respective IC₅₀ values.

Fig. 2

Synthesis of thiosemicarbazone derivatives 5(a-y).

Fig. 3

Potency landscape of synthesized compounds compared to the standard inhibitor acarbose. IC₅₀ values (µM, log scale) are shown for each compound, with fold-improvement in potency relative to acarbose indicated above each bar.

Fig. 4

SAR illustration of newly synthesized compounds 5(a-y).

Fig. 5

The inhibition of α-glucosidase by compound 5u (A) Line weaver-Burk plot of reciprocal of rate of reaction (velocities) vs. reciprocal of substrate concentration in the absence of (■), and in the presence of 10.00 µM (○), 5.00 µM (●), and 2.50 µM (□) of compound 5u. (B) Secondary replot of the Line weaver-Burk plot between the slopes of each line on the Line weaver-Burk plot vs. different concentrations of compound 5u. (C) Dixon plot of the reciprocal of the rate of reaction (velocities) vs. different concentrations of compound 5u.

Fig. 6

Overlap of docked conformations of compounds 5(a-y) with acarbose (black). The zoomed in region shows overlap of most active inhibitor 5u with acarbose.

Fig. 7

Docked conformation of 5u with α-glucosidase showing binding site interactions.

Fig. 8

Docked conformation of 5p with α-glucosidase showing binding site interactions.

Fig. 9

Comparison of 2D docked conformation of inhibitors 5b and 5k.

Fig. 10

RMSD and protein RMSF graphs of 5u-α-Glucosidase complex for 150 ns simulation.

Fig. 11

Superimposed structure poses of 5u during simulation at different time intervals, Yellow at 0 ns, Green at 30 ns, Magenta at 100ns, and Orange-red at 150 ns, respectively.

Fig. 12

Ligand RMSF and protein-ligand contacts, of inhibitor 5u with α-glucosidase during the simulation.

Fig. 13

Ligand-protein contacts and ligand-torsion profile of inhibitor 5u with α-glucosidase during the simulation.

Fig. 14

[A] PCA summary of alpha carbon atoms of 5u-alphaglucosidase complex; [B] PCA summary of binding site residues within 5 Å of 5u, excluding 5u’s atoms in 5u-alphaglucosidase complex. [C] PCA summary of binding site residues within 5 angstroms of 5u, including 5u’s atoms in 5u-alphaglucosidase complex.

Fig. 15

Three-dimensional graph of free energy landscape analysis of 5u α-glucosidase simulation.

Fig. 16

Optimized structures of the investigated compounds at DFT/B3LYP/6-311G(d, p)/GD3 calculations in the gas phase.

Fig. 17

HOMO-LUMO diagram of investigated compounds.

Fig. 18

Molecular electrostatic potential (MEP) maps for the investigated compounds at B3LYP/6–311 g(d, p)/GD3 level of theory in the gas phase.