2-Amino-6-sulfamoylbenzothiazole (SMABT) and its proton transfer compound (HSMABT)(+)(HDPC)(-) (1) with 2,6-pyridinedicarboxylic acid (H2DPC), and their Cu(II) complexes (2 of SMABT, 3 and 4 of 1) have been prepared and characterized by spectroscopic techniques. Additionally, single crystal X-ray diffraction techniques were applied to all complexes. All compounds, including acetazolamide (AAZ) as the control compound, were also evaluated for their in vitro inhibition effects on human hCA I and hCA II for their hydratase and esterase activities. The synthesized complexes have remarkable inhibitory effects on hCA I and hCA II isoenzymes. The inhibition potentials of the proton transfer salt (1) and the metal complexes (2-4) are comparable with AAZ. Esterase K-i values of the compounds (1-4) are in the range of 0.089 +/- 0.008 mu M-0.149 +/- 0.017 mu M for hCA I and 0.046 +/- 0.008 mu M-0.085 +/- 0.019 mu M for hCA II. Inhibition data have been analyzed by using a one-way analysis of variance for multiple comparisons (p < 0.0001). (C) 2018 Published by Elsevier Ltd.