Novel hydroxybenzylamine-deoxyvasicinone hybrids as anticholinesterase therapeutics for Alzheimer's disease

Abstract

A series of novel 2-hydroxybenzylamine-deoxyvasicinone hybrid analogs (8a-8n) have been synthesized and evaluated as inhibitors of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE), and as inhibitors of amyloid peptide (Aβ_1-42) aggregation, for treatment of Alzheimer's disease (AD). These dual acting compounds exhibited good AChE inhibitory activities ranging from 0.34 to 6.35 µM. Analogs8g and 8n were found to be the most potent AChE inhibitors in the series with IC₅₀values of 0.38 µM and 0.34 µM, respectively. All the analogs (8a-8n) exhibited weak BuChE inhibitory activities ranging from 14.60 to 21.65 µM. Analogs8g and 8n exhibited BuChE with IC₅₀values of 15.38 µM and 14.60 µM, respectively, demonstrating that these analogs were greater than 40-fold more selective for inhibition of AChE over BuChE. Additionally, compounds8g and 8n were also found to be the best inhibitors of self-induced Aβ_1-42 peptide aggregation with IC₅₀values of 3.91 µM and 3.22 µM, respectively; 8g and 8n also inhibited AChE-induced Aβ_1-42 peptide aggregation by 68.7% and 72.6%, respectively. Kinetic analysis and molecular docking studies indicate that analogs 8g and 8n bind to a new allosteric pocket (site B) on AChE. In addition, the observed inhibition of AChE-induced Aβ_1-42 peptide aggregation by 8n is likely due to allosteric inhibition of the binding of this peptide at the CAS site on AChE. Overall, these results indicate that 8g and 8n are examples of dual-acting lead compounds for the development of highly effective anti-AD drugs.

Keywords: 2-Hydroxybenzylamine; Acetylcholinesterase inhibitors; Alzheimer’s disease; Aβ(1-42) peptide Aggregation; Deoxyvasicinone.

Fig 1.

Chemical structures of MTDL agents: 2-hydroxybenzylamine-flurbiprofen hybrid (1), 2-hydroxybenzylamine-tacrine hybrid (2) vasicinone (3a) and deoxyvasicinone (3b)

Fig 2.

Design strategy for the synthesis of 2-hydroxybenzylamine-deoxyvasicinone hybrids

Fig 3.

Inhibition of AChE-induced Aβ_1–42 peptide aggregation by compounds 8a, 8d, 8g, 8h, 8k, 8n, 3b and clioquinol.

Fig 4.

Lineweaver-Burk plots for inhibition of AChE by compound 8n

Fig 5.

(A) Positions of the allosteric site B and the CAS/PAS gorge in the AChE crystal structure (PDB #: 1N5R). Hybrid molecule 8n binds to site B and not the CAS site, which explains the observed non-competitive inhibition (B). Key interactions of 8n at the site B allosteric site. Hydrogen bonds and π-π interactions are illustrated in blue and brown dashed lines, respectively.

Fig 6.

Interactions of Aβ_1–42 peptide with AChE (yellow) shows that the peptide binds at the PAS site (black circle).

Scheme 1.

Synthesis of deoxyvasicinone analogs 8a-8n. Reagents and conditions: (a) i) HNO₃, H₂SO₄, −10 °C, 3h; ii) Na₂S·9H₂O, NaOH, EtOH, reflux, 4h; (b) appropriate salicylaldehyde, CH₃OH/THF, 2–3 h at 22°C; (c) NaBH₄, CH₃OH/THF, 1 h at 22°C.