Synthesis, characterization and antiglaucoma activity of a novel proton transfer compound and a mixed-ligand Zn(II) complex Original Research Article

A novel proton transfer compound, pyridin-2-ylmethanaminium 2,4-dichloro-5-sulfamoylbenzoate (1), and a mixed-ligand Zn(II) complex, bis(2,4-dichloro-5-sulfamoylbenzoate)(2-aminomethylpyridine)aquazinc(II) monohydrate (2), have been synthesized from the same free ligands, which are 2,4-dichloro-5-sulfamoylbenzoic acid (Hsba) and 2-aminomethylpyridine (amp). They have been characterized by elemental, spectral (1H NMR, IR and UV–vis.) and thermal analyses. Additionally, magnetic measurement and single crystal X-ray diffraction technique were applied to compound 2. In the complex, Zn(II) ion exhibits a distorted octahedral configuration coordinated by O1 and O1i atoms of two mono dentante sba anions and N1, N2, N2i atoms of bidentante amp anion and a water molecule (O1w). The free ligands Hsba and amp, and the products 1 and 2, and acetazolamide (AAZ) as the control compound, were also evaluated for their in vitro inhibitor effects on human Carbonic Anhydrase isoenzymes (hCA I and hCA II) purified from erythrocyte cell by affinity chromatography for their hydratase and esterase activities. The IC50 values of products 1 and 2 for hydratase activity are 0.26 and 0.13 μM for hCA I and 0.30 and 0.15 μM for hCA II, respectively. The IC50 values of the same inhibitors for esterase activity are 0.32 and 0.045 μM for hCA I and 0.29 and 0.23 μM for hCA II, respectively. In relation to esterase activities, the inhibition equilibrium constants (Ki) were also determined and found 0.25 and 0.058 μM on hCA I and 0.22 and 0.24 μM on hCA II for 1 and 2, respectively. The comparison of the inhibition studies of newly synthesized compounds 1 and 2 to parent compounds Hsba and amp and to AAZ indicated that 1 and 2 have effective inhibitory activity on hCA I and II, and might be used potential inhibitors.