Carbonic anhydrase inhibitory activities of novel proton transfer salts and their Cu(II) complexes

In this study, two new proton transfer salts of sulfonamide derivatives of maleic acid, namely (ClHabt)+(mabsmal)– (1) and (ClHabt)+(pabsmal)– (2), were obtained from 2-amino-6-chlorobenzo­thiazole (Clabt) and N-(3-sulfamoylphenyl)maleamide acid (Hmabsmal) and N-(4-sulfamoyl­phenyl)maleamide acid (Hpabsmal), respectively. Also, the Cu(II) complexes (3 and 4) of salts (1 and 2) and of Hmabsmal (5) were prepared. Compounds 1‒5 were characterized by elemental, NMR (1H and 13C), FTIR, and thermal analyses, as well as UV-Vis, magnetic moment, and molar conductivity measurements. Carbonic anhydrase isoenzymes (hCA I and II) were purified from human erythrocyte cells by affinity chromatography. The effects of the synthesized compounds on the hydratase and esterase activities of CA isoenzymes were studied in vitro. The results reveal that the synthesized compounds inhibit both esterase and hydratase activities of hCA I and hCA II. The inhibition constants of the compounds (Ki) were determined according to the esterase activity measurements. Ki values of 1‒5 are in the range of 0.06 ± 0.003 µM and 4.25 ± 0.100 µM for hCA I, and of 0.02 ± 0.001 µM and 3.21 ± 0.200 µM for hCA II.