On the basis of the above information we designed
On the basis of the above information, we designed a new series of benzothiazole–piperazine derivatives (–) that have the aforementioned structural requirements (). Benzothiazole is an important ring system in the drug discovery studies of AD. There are several benzothiazole compounds that show potential therapeutic effects against AD., , , , , , Furthermore, sabeluzole, a benzothiazole agent, delays the clinical progression of AD., Thus, we selected benzothiazole as a core ring system. Structural similarity of benzothiazole with donepezil and BYYT-25 was increased by mitotic inhibitors with methoxy at the C5 and C6 positions. The basic centre was established by bioisosterically replacing piperidine with piperazine because numerous piperazine compounds have been reported as cholinesterase inhibitors., , , , In the present study, we synthesised novel compounds investigate their AChE inhibition potential. The compounds – were synthesised as shown in . In the first step, 2-aminobenzothiazole derivatives ( and ) were prepared via reaction of appropriate aniline ( and ), potassium thiocyanate, and bromine. In the second step, 2-chloro--(benzothiazol-2-yl)acetamide derivatives ( and ) were synthesised via acetylation reaction by using chloroacetyl chloride. Finally, substitution reaction between corresponding 1-substituted piperazines and 2-chloro--(benzothiazol-2-yl)acetamide derivatives ( and ) yielded the target compounds –. The structures of the newly synthesised compounds (–) were elucidated using IR, H NMR, C NMR, and HRMS methods. Assessment of the compounds – as AChE (E.C.22.214.171.124, from electric eel) inhibitors was carried out using the modified Ellman’s spectrophotometric method. We used donepezil as the reference drug in the enzymatic activity for the above process. synthesised compounds – along with donepezil were tested at 10–10 M concentrations. The IC values obtained for these compounds are presented in . All the compounds showed remarkable AChE inhibition activity. At 10 M concentration, the inhibition rate of all the compounds was more than 50%. Compounds , , , and also showed more than 50% inhibition at 10M concentration. Compounds , , and showed more than 95% enzyme inhibition at 10 M concentration and approximately 90% enzyme inhibition at 10M concentration. Regarding AChE inhibitory activity, all of the 6-methoxybenzothiazole derivatives (–) were less potent than the 5,6-dimethoxybenzothiazole compounds (–) were. Compounds containing the dimethylaminoethyl ( and ) and dimethylaminopropyl ( and ) moieties at the fourth position of piperazine showed stronger inhibition than did the compounds – and – that carry benzyl substitutions at the same position. Compounds and , which possess these two structural features, were found to be the most active derivatives in the series. The IC values of donepezil, compound , and compound were found to be 0.0287, 0.0462, and 0.0576μM, respectively. These data indicate that the AChE inhibition potential of compounds and is close to that of donepezil. The other compounds (–) also have good IC in the range of 0.0942–0.3965μM. As a result, all the newly synthesised compounds turned out to be potent inhibitors of AChE with a low micromolar range of IC. The mechanism of AChE inhibition was investigated via enzyme kinetics by using the Ellman’s spectrophotometric method. Linear Lineweaver–Burk graphics were used to observe the type of inhibition. Further, we analysed the enzyme kinetics by recording substrate–velocity curves in the absence and presence of the most potent compound (IC=0.0462μM). In each case, initial velocity measurements were obtained at different substrate (ATC) concentrations ranging from 600μM to 18.75μM. The (intercept on the -axis) values of the compounds and were calculated from the secondary plot of the 1/ versus concentrations of compounds. The graphical analyses of steady-state inhibition data for the compounds and are presented in , . Very similar effects of these compounds on enzyme kinetics were observed. In the figures, the lines cross neither - nor -axis at the same point. Different and values were obtained for various concentrations that are presented along with the values in . Thus, the Lineweaver–Burk plot reveals that compounds and are typically mixed AChE inhibitors, which show significant similarity to donepezil., The result also indicates that both these compounds interact with both CAS and PAS of AChE.