hCAIX-IN-21 (compound 16c) is an effective inhibitor of hCAIX, exhibiting KI values of 5.2 nM, 3.5 nM, 12.6 nM, and 13600 nM against hCAIX, hCA II, hCA XII, and hCA I, respectively. Moreover, it inhibits the enzymatic activity of tissue protease B.

hCA IX:5.2 nM (Ki), hCA XII:12.6 nM (Ki), hCA II:3.5 nM (Ki), hCA I:13600 nM (Ki)