Unveiling the potential of novel indol-3-yl-phenyl allylidene hydrazine carboximidamide derivatives as AChE/BACE 1 dual inhibitors: a combined in silico, synthesis and in vitro study

Abstract

Considering the failure of many enzyme inhibitors for Alzheimer's disease (AD), research is now focused on multi-target directed drug discovery. In this paper, inhibition of two essential enzymes implicated in AD pathologies, acetylcholinesterase (AChE) and BACE 1 (Beta-site APP Cleaving Enzyme), has been explored. Taking clues from our previous work, 41 novel indol-3-yl phenyl allylidene hydrazine carboximidamide derivatives were synthesized. The results indicated that compounds inhibited both enzymes in micromolar concentrations. Compound 1l is proposed as the most active. In silico, it was seen to occupy the binding pocket of AChE and BACE 1. The ADME predictions showed that these compounds have acceptable physicochemical characteristics. This study provides new leads for the assessment of AChE and BACE 1 dual inhibition as a promising strategy for AD treatment.

Fig. 1. US FDA approved drugs for the treatment of Alzheimer's disease.

Fig. 2. Designing strategy for the development of indole-based dual inhibitors using molecular hybridization approach.

Scheme 1. Reagents and conditions: (i) substituted benzyl bromide, KOH, DMF, ultra-sonication, 25 °C, 1 h (ii) substituted benzaldehyde, NaOH, EtOH, ultra-sonication, 25 °C, 30 min (iii) aminoguanidine-HCl, conc. HCl, EtOH, ultra-sonication, 25 °C, 2.0 h.

Fig. 3. Docking validation of 4EY7 and 6UWP (A) redocked pose of donepezil (red) superimposed with the co-crystallized ligand (yellow) (RMSD: 0.14 Å, Glide score:14.56); (B) redocked pose of QKA (red) superimposed with the co-crystallized ligand (green) (RMSD: 0.08 Å, Glide score:9.64); (C) and (D) show overlapping of all of the docked compounds within the active site of 4EY7 and 6UWP, respectively.

Fig. 4. (A) 2D interaction plot of 1l in AChE (Glide score-11.08 kcal mol⁻¹); (B) 2D interaction plot of 1l in BACE 1 (Glide score-10.98 kcal mol⁻¹).

Fig. 5. (A) 2D interaction plot of 3j in 4EY7 (Glide score-12.05 kcal mol⁻¹); (B) 2D interaction plot of 3j in BACE 1 (Glide score-6.89 kcal mol⁻¹).

Fig. 6. Molecular dynamics studies of 1l-AChE (4EY7) docked complex. [A] Comparative RMSD of AChE (protein backbone) and compound 1l in the protein–ligand complex throughout the simulation period of 100 ns. [B] Graphical representation showing interactions with active site amino acid residues of PAS and CAS; [C] histogram showing interaction fractions with active amino acid residues; [D and E] timeline representation showing interaction with all the amino acid residues at each time frame.

Fig. 7. Molecular dynamics studies of 1l-BACE 1 (PDB ID: 6UWP) docked complex. [A] Comparative RMSD of BACE 1 (protein backbone) and compound 1l in the protein–ligand complex throughout the simulation period of 100 ns. [B] Graphical representation showing interactions with active site amino acid residues (aspartate dyad); [C] histogram showing interaction fractions with active amino acid residues; [D and E] timeline representation showing interaction with all the amino acid residues at each time frame.

Fig. 8. Structure Activity Relationship (SAR) study of indol-3-yl-phenyl allylidene hydrazine carboximidamides analogues.