Structure-based search for new inhibitors of cholinesterases

Abstract

Cholinesterases are important biological targets responsible for regulation of cholinergic transmission, and their inhibitors are used for the treatment of Alzheimer's disease. To design new cholinesterase inhibitors, of different structure-based design strategies was followed, including the modification of compounds from a previously developed library and a fragment-based design approach. This led to the selection of heterodimeric structures as potential inhibitors. Synthesis and biological evaluation of selected candidates confirmed that the designed compounds were acetylcholinesterase inhibitors with IC50 values in the mid-nanomolar to low micromolar range, and some of them were also butyrylcholinesterase inhibitors.

Figure 1

Cholinesterases inhibitors used in Alzheimer’s disease (AD) treatment. Tacrine was withdrawn, due to its hepatotoxicity, but it is still used in experiments as a reference inhibitor.

Figure 2

Active site of acetylcholinesterase (Torpedo californica acetylcholinesterase (TcAChE); Protein Database Bank (PDB): 1EVE).

Figure 3

Active site of butyrylcholinesterase (human butyrylcholinesterase (hBuChE), PDB: 1P0I).

Figure 4

Superimposed amino acid residues from the AChE active site, derived from different crystal structures (1ACJ: yellow; 1EVE: blue; 2ACE: red; 2CKM: green).

Figure 5

The starting point of our research—compounds 1 and 2. They are both acetyl- and butyryl-cholinesterase inhibitors with micromolar IC₅₀ values [32].

Figure 6

Tacrine clusters obtained in docking to BuChE. Results were compared with the arrangement of tacrine (orange) in the complex with acetylcholinesterase.

Figure 7

Modifications of heterodimeric compounds 1 and 2.

Figure 8

The obtained derivative 3, based on our library of compounds.

Figure 8

The obtained derivative 3, based on our library of compounds.

Figure 9

Structural fragments used for the fragment-based design of cholinesterase inhibitors. ChemScore values for binding with acetylcholinesterase are given for each fragment.

Figure 10

Structures of designed acetylcholinesterase inhibitors—newly synthesized (4–6) and currently described compounds (7–9).

Figure 11

Reagents and conditions: i. dibromoalkane, tetra-n-butylammonium bromide (TBAB), MeCN, reflux, 20 h; ii. (a) 4-amino-1-benzylpiperidine, triethylamine (TEA), MeCN, reflux, 3 h (compound (cmp.) 1,2); (b) 1-(3-chlorobenzyl)piperidin-4-amine, TEA, MeCN, microwave (MW), 100 °C, 45 min. (cmp. 3); (c) benzylamine, K₂CO₃, MeCN, room temperature (RT), 48 h (cmp. 4,5); (d) 2-fluorobenzylamine, K₂CO₃, MeCN, RT, 48 h (cmp. 6).