Twenty-five new N-[4-(benzothiazole-2-yl)phenyl]acetamide derivatives bearing different heterocyclic ring systems were synthesized using 2-(4-aminophenyl

The acid dissociation constants of some 4-and/or 6-substituted 2-aminobenzothiazole and 4-substituted thiazole derivatives were determined spectroscopically. With the exception of a few, the first protonation was found to occur on the amino group. In some molecules where prototropic tautomerism is possible, a change-over in the protonation mechanism was observed. The first protonation under these circumstances was found to occur on the imino nitrogen atom. The second protonation takes place on the thiazole ring nitrogen atom.

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Two new series of 1,3,4‐oxadiazoles bearing pyridine and thiazole heterocycles (4a‐h and 5a‐h) were synthesized (2,5‐disubstituted‐1,3,4‐oxadiazoles). The structures of these newly synthesized compounds were confirmed by 1H nuclear magnetic resonance (NMR), 13C NMR, high‐resolution mass spectrometric and Fourier transform infrared spectroscopic methods. All these compounds were evaluated for their enzyme inhibitory activities against two cholinesterase enzymes, acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). From the studies, we identified compounds 4a, 4h, 5a, 5d, and 5e as selective AChE inhibitors, with IC50 values ranging from 0.023 to 0.037 μM. Furthermore, docking studies of these compounds were performed at the active sites of their target enzymes. The molecular docking study showed that 5e possessed an ideal docking pose with interactions inside AChE.

The acid dissociation constants, K a , of nine biologically active 2-amino-4-(x-pyridyl)-thiazole, 2-methylimino-3-methyl-4-(x-pyridyl)-2,3-dihydrothiazole, and 2-methylamino-4-(x-pyridyl)-2,3-dihydrothiazole were determined using UV-vis spectroscopic technique.The acidity constants for the first protonation, pK a1 , of parent molecules and their fixed model molecules are found to be associated with the protonation of aza or imino nitrogen atom. The acidity constants for the second proton uptake, pK a2 , are found to correspond to aza, imino, or amino nitrogen atom protonation. The contribution of the imino tautomeric form to tautomeric equilibria was found to be considerably important.