Alzheimer’s disease (AD) is a complex, progressive neurodegenerative disorder characterised by pathological changes in the central nervous system, including cholinergic dysfunction, accumulation of amyloid beta plaques and oligomers, hyperphosphorylation of the tau protein, and neuroinflammation. An important target in the development of new therapeutic agents targeting AD is the enzyme butyrylcholinesterase (BChE), as it plays a significant role in the deterioration of cognitive functions by influencing signal transmission within the cholinergic system.
In this Master’s thesis, five new covalent inhibitors of BChE were designed, synthesized, and evaluated, based on the lead compound DP-802. In this compound, the urea group was replaced with a carbamate moiety to enable covalent binding to Ser198 of BChE. Additionally, the acetamide group on the benzene ring was replaced with a nitrile group, improving the solubility of synthetic intermediates in organic solvents used during synthetic process, without compromising the solubility of the final compounds in aqueous buffer. Various substituents were introduced on the carbamate moiety to evaluate their contribution to covalent binding to the target enzyme. Ligand design also focused on achieving improved selectivity for BChE over acetylcholinesterase (AChE).
Five final compounds (8a-8e) were synthesized and isolated and tested in vitro against human acetylcholinesterase (hAChE) and butyrylcholinesterase (hBChE) using Ellman’s assay. Compound 8d was identified as the most potent BChE inhibitor, with a benzyl fragment providing approximately two orders of magnitude higher inhibitory activity compared to a directly attached phenyl fragment on the nitrogen atom. Nevertheless, the compounds did not exhibit pronounced selectivity for hBChE, as compounds 8c and 8d showed only about 10-fold selectivity over hAChE, whereas at least a 1000-fold difference would be required. However, compounds 8c and 8d demonstrated pseudo-irreversible inhibition of the target enzyme.
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