Carbonic Anhydrase Inhibitors. Comparison of Chlorthalidone and Indapamide X-ray Crystal Structures in Adducts with Isozyme II: When Three Water Molecules and the Keto-Enol Tautomerism Make the Difference.

[摘要]：Thiazide diuretics inhibit all mammalian isoforms of carbonic anhydrase (CA, EC 4.2.1.1) with a different profile as compared to classical inhibitors. Acting as moderate-weak inhibitors of CA II and CA I, chlorthalidone and indapamide considerably inhibit other isoenzymes among the 16 CAs present in vertebrates. These compds. show a different behavior against CAs I and II, with chlorthalidone being 18.3 times more potent against CA II and 150 times more potent against CA I, as compared to indapamide. In the X-ray crystal structures of the CA II-chlorthalidone adduct three active site water mols. interacting with the inhibitor scaffold were obsd. that lack in the corresponding indapamide adduct. Chlorthalidone bound within the active site is in an enolic tautomeric form, with the OH moiety participating in two strong hydrogen bonds with Asn67 and a water mol. This binding mode may be exploited for designing better CA II inhibitors.

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