hCAIX/XII-IN-8 (compound 3g) is a potent human ( carbonic anhydrase ) CA IX and XII inhibitor, with K i values of 8.5 and 6.7 nM, respectively. hCAIX/XII-IN-8 shows particularly strong inhibitory activity against the tumor-associated membrane-bound isoforms, hCA IX and XII, while maintaining a high selectivity ratio over cytosolic off-target isoforms hCA I and II.