hCAII-IN-6 (Compound S-13), a potent inhibitor of human carbonic anhydrase II (hCA II) with a K i of 4.4 nM, also exhibits inhibitory activity against other hCA isoforms, namely I, IV, and IX, with K i values of 9.2 nM, 480.2 nM, and 14.7 nM, respectively. It is utilized in glaucoma research [1].