Thiazole-substituted benzoylpiperazine derivatives as acetylcholinesterase inhibitors

Hit, Lead & Candidate Discovery After acetylcholine is released into the synaptic cleft, it is reabsorbed or deactivated by acetylcholinesterase (AChE). Studies on Alzheimer's disease (AD) in the mid-20th century proved that cognitive dysfunctions are associated with cholinergic neurotransmission. Drugs, such as tacrine, rivastigmine, donepezil, and galantamine are known as acetylcholinesterase inhibitors. However, these drugs have limited use in advanced AD and dementia. Recently, the anticholinesterase activity of various heterocyclic-framed compounds, including piperazine derivatives, has been investigated, and compounds with similar effects to known drugs have been identified. The aim of this study was to design new donepezil analogs. In this study, 66 original piperazinyl thiazole derivatives were synthesized by the reaction of piperazine N'-benzoyl thioamides and bromoacetophenones to inhibit AChE. Biological activity was measured by the Ellman method. Compounds 35, 38, 40, 45, 57, and 61 showed a high inhibitory effect among the series (80.36%-83.94% inhibition), and donepezil had a 96.42% inhibitory effect. The IC₅₀ values of compounds 35, 38, and 40, were calculated as 0.9767 μM, 0.9493 μM, and 0.8023 μM, respectively. Compound 45 (IC₅₀ = 1.122), Compound 57 (IC₅₀ = 1.2130) and 61 (IC₅₀ = 0.9193) also exhibited good activity on AChE. Molecular modeling studies were in agreement with the predictions. Trp286, Arg296, and Tyr341 were the key amino acids at the active site. Both donepezil and synthesized compounds seemed to interact with these residues.