From tryptamine to the discovery of efficient multi-target directed ligands against cholinesterase-associated neurodegenerative disorders

Abstract

A novel class of benzyl-free and benzyl-substituted carbamylated tryptamine derivatives (CDTs) was designed and synthesized to serve as effective building blocks for the development of novel multi-target directed ligands (MTDLs) for the treatment of neurological disorders linked to cholinesterase (ChE) activity. The majority of them endowed butyrylcholinesterase (BuChE) with more substantial inhibition potency than acetylcholinesterase (AChE), according to the full study of ChE inhibition. Particularly, hybrids with dibenzyl groups (2b-2f, 2j, 2o, and 2q) showed weak or no neuronal toxicity and hepatotoxicity and single-digit nanomolar inhibitory effects against BuChE. Through molecular docking and kinetic analyses, the potential mechanism of action on BuChE was first investigated. In vitro H₂O₂-induced HT-22 cells assay demonstrated the favorable neuroprotective potency of 2g, 2h, 2j, 2m, 2o, and 2p. Besides, 2g, 2h, 2j, 2m, 2o, and 2p endowed good antioxidant activities and COX-2 inhibitory effects. This study suggested that this series of hybrids can be applied to treat various ChE-associated neurodegenerative disorders such as Alzheimer's disease (AD) and Parkinson's disease (PD), as well as promising building blocks for further structure modification to develop efficient MTDLs.

Keywords: MTDLs; anti-neuroinflammation; benzylation; carbamylated tryptamine derivatives; cholinesterase inhibitors; neurodegenerative disorders; neuroprotection; promising building blocks.

SCHEME 1

(A) Structures of several represented tryptamine derivatives. (B) Structures of several represented carbamate-based drugs. (C) Structures of several represented benzyl-containing agents with pharmaceutical activities.

FIGURE 1

Design strategy for developing promising building blocks for MTDLs against ChE-associated neurodegenerative disorders.

SCHEME 2

Synthetic method for the targeted carbamylated tryptamine derivatives.

FIGURE 2

The possible binding mode for the compounds 2h, 2i, 2s, 2u in the BuChE (PDB code: 4TPK) binding sites. (A,B,E,F) The 2D images of 2h, 2i, 2s, 2u, respectively, binding to BuChE predicted by Schrodinger software (Release 2019-2, Schrodinger, LLC, New York, NY, 2019). The purple arrow indicates hydrogen bond, the red arrow indicates π–cation interaction, and the green line indicates π–π interaction. (C,D) The potential distribution surface diagrams of 2s and 2u, respectively, created by Pymol (http://www.pymol.org).

FIGURE 3

Outline of SARs of compounds 2a-2u and 3a-3u on BuChE.

FIGURE 4

Outline of SARs of compounds 3a-3u on AChE.

FIGURE 5

The possible binding mode for the selected compounds in the BuChE (PDB code: 4TPK) binding sites (A–O). The 3D images of selected compounds bind to BuChE polished by Pymol (http://www.pymol.org). Residues of the acyl-binding pocket (Leu286, Trp231) are shown in magenta, the CAS (His438) is shown in pink, the choline-binding site (Trp82) is shown in orange, the residues of PAS (Asp70, Thr120, Tyr332, and Phe329) are shown in yellow, and parts of the side cavity (Pro285, Ala328) are in pale cyan. The dashed lines indicate hydrogen bond interaction, π–π stacking interactions, or π–cation interactions.

FIGURE 6

The possible binding mode for the compounds 2q and 3q in the AChE (PDB code: 4M0F) binding sites. (A,C) The 2D images of 2q and 3q binding to AChE predicted by Schrodinger software (Release 2019-2, Schrodinger, LLC, New York, NY, 2019). The purple arrow indicates hydrogen bond, the red arrow indicates π–cation interaction, and the green line indicates π–π stacking interaction. (B,D) The 3D images of 2q and 3q binding to AChE polished by Pymol (http://www.pymol.org). Residues of the CAS (His447) are shown in orange, and the residues of PAS (Ser293, Trp286, Tyr337, Trp86, and Tyr341) are shown in yellow. The dashed lines indicate hydrogen bond interaction, π–π stacking interactions, or π cation interactions.

FIGURE 7

The possible binding mode for the compounds 2e and 2f in the AChE (PDB code: 4M0F) and BuChE (PDB code: 4TPK) binding sites. (A,B) The potential distribution surface diagrams of 2e in AChE and BuChE binding sites, respectively, created by Pymol (http://www.pymol.org). (C,D) The potential distribution surface diagrams of 2f in AChE and BuChE binding sites, respectively, created by Pymol (http://www.pymol.org).

FIGURE 8

(A) The reported pseudo-irreversible inhibition mode of carbamylated derivatives on ChE. (B) The equilibrium constant (k_c) values of tested compounds. (C) The carbamylation rate constant (k₃) values of tested compounds. (D) The k₃/k_c values of the tested compounds. All these data are the mean ± SD of triplicate in three independent experiments.

FIGURE 9

Cell viability was examined by MTT assay. Neuroprotective effects of tested compounds against the toxicity elicited by 500 μM H₂O₂. HT-22 cells were co-incubated with H₂O₂ and the tested compounds (5 and 10 μM) for 24 h. The values were expressed as mean ± SD of three independent experiments. ^### p < 0.001 compared to the control group. ***p < 0.001, **p < 0.01, or *p < 0.05 compared to the H₂O₂ induced model group. Riv, rivastigmine.

FIGURE 10

Results are expressed in the Trolox equivalents (TE) unit. The values were expressed as mean ± SD of three independent experiments.

FIGURE 11

IC₅₀ is the concentration (μМ) that causes 50% inhibition of COX-2 enzymatic activity. The values were expressed as mean ± SD of three independent experiments.