Carbonic anhydrase inhibitor 20 (compound 11) is an inhibitor of piperazinosulfonamide carbonic anhydrase ( Carbonic Anhydrase ). The Ki of Carbonic anhydrase inhibitor 20 for hCA I, hCA II, hCA IX, and hCA XII are 47.6 nM, 36.5 nM, 8.3 nM, and 2.7 nM respectively.