Carbonic Anhydrase Inhibitors. Comparison of Aliphatic Sulfamate/Bis-sulfamate Adducts with Isozymes II and IX as a Platform for Designing Tight-Binding, More Isoform-Selective Inhibitors

Two approaches were used to design inhibitors of the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1): the tail and the ring approaches. Aliphatic sulfamates constitute a class ofCAinhibitors (CAIs) that cannot be classified in either one of these categories. Wereport here the detailed inhibition profile of four such compounds against isoforms CAs I-XIV, the first crystallographic structures of these compounds in adduct with isoform II, and molecular modeling studies for their interaction with hCA IX. Aliphatic monosulfamates/bis-sulfamates were nanomolar inhibitors of hCAs II, IX, and XII, unlike aromatic/heterocyclic sulfonamides that promiscuously inhibit most CA isozymes with low nanomolar affinity. The bis-sulfamates incorporating 8 or 10 carbon atoms showed higher affinity for the tumor-associated hCA IX compared to hCA II, whereas the opposite was true for the monosulfamates. The explanation for their interaction with CA active site furnishes insights for obtaining compounds with increased affinity/selectivity for various isozymes. Introduction A paradigm in carbonic anhydrase (CA,a EC 4.2.1.1) drug design was that aliphatic sulfonamidesRSO2NH2 (R=aliphatic group) are inactive as inhibitors, unlike the aromatic/heterocyclic ones of the type ArSO2NH2.1 This view was subsequently challenged, being shown that aliphatic sulfonamides incorporating perhaloalkyl moieties of the type CnX2nþ1SO2- NH2 (n=1-4, X=F, Cl),2 as well as various aliphatic sulfamates/bis-sulfamates3-5 potently inhibit several CA isozymes involved in fundamental physiologic/pathologic states. Indeed, this family of metalloenzymes comprises 16 different isoforms, of which several are cytosolic (CAs I-III, CA VII, and CAXIII), five are membrane-bound (CA IV, CAIX, CA XII, CA XIV, and CA XV), two are mitochondrial (CAs VA and VB), and one (CA VI) is secreted into saliva/milk.6-13 Three acatalytic forms are also known, i.e., CA VIII, CA X, and CA XI.9 These enzymes are involved in crucial physiological processes connected with respiration and transport of CO2/bicarbonate betweenmetabolizing tissues and lungs, pH and CO2 homeostasis, electrolyte secretion in a variety of tissues/organs, biosynthetic reactions (such as gluconeogenesis, lipogenesis, and ureagenesis), bone resorption, calcification, tumorigenicity, and