A series of novel 4-substituted-3-pyridinesulfonamides (2-27 and 31-33) have been synthesized and investigated as inhibitors of five isoforms of zinc enzyme carbonic anhydrase (CA, EC 4.2.1.1), that is, the cytosolic, ubiquitous isozymes CA I and II, and transmembrane isozymes CA IX, XII (cancer-associated) and XIV. Against the human isozymes hCA I, the new compounds showed inhibition constants in the range of 0.078-11.7 microM, against hCA II in the range of 9.9-140 nM, against hCA IX in the range of 4.6-313 nM, against hCA XII in the range of 3.4-21.6 nM, and against hCA XIV in the range of 50.9-160 nM, respectively. Compounds 4, 6, 7, 9, 11-14, 19, 20, 22-24, 26, 27, 31 and 32 showed excellent hCA IX inhibitory efficacy, with inhibition constants of 4.6-12.0 nM, being much more effective as compared to the clinically used sulfonamides AAZ, MZA, EZA, DCP and IND. 4-[N'-(6-chloro-7-cyano-1,1-dioxo-1,4,2-benzodithiazin-3-yl)hydrazino]-3-pyridinesulfonamide (31) is the prominent of the compounds due to its remarkable inhibitory activity toward hCA I (KIs=0.078 microM), hCA IX (KIs=7.2 nM) and hCA XII (KIs=3.4 nM).
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