Synthesis, Enzyme Inhibition, and Acid Dissociation Constant of 1,4-Naphthoquinone Thiazole Hybrid

In this study, N-((Z)-4-((3r,5r,7r)-adamantan-1-yl)-3-(3-amino-1,4-dioxo-1,4-dihydronaphthalen-2yl)thiazol-2(3H)-ylidene)-2,6-difluorobenzamide 3 was synthesized as a new 1,4-naphthoquinone thiazole hybrid compound by reaction of naphthoquinone acyl thiourea compound 2 with 1-((3r,5r,7r)-adamantan-1-yl)-2-bromoethan-1-one in 74% yield and its molecular structure was characterized by various analytical techniques such as 1H/13C NMR, FT-IR, and HRMS. The inhibition effect of the synthesized compound on butyrylcholinesterase (BChE), acetylcholinesterase (AChE), and human carbonic anhydrase isoenzymes (hCA I and hCA II) was investigated. The product 3 showed varying degrees of inhibition 89.92 ± 10.47 nM (against hCA I), 51.60 ± 5.37 nM (against hCA II), 68.11 ± 6.58 nM (against AChE), and 126.90 ± 10.99 (against BChE). Although 1,4-naphthoquinone thiazole hybrid 3 showed significant enzyme activity against the enzymes tested, it showed a higher inhibition activity against the AChE enzyme than the standard drug Tacrine. Three acid dissociation constants (pKa) values (pKa1= 2.75±0.02, pKa2= 6.79±0.02, pKa3= 10.85±0.02) of the product were determined potentiometrically in 0.1 M NaCl ionic strength at 25.0±0.1 ºC in 25% (v/v) DMSO:water hydro organic medium.