Carbonic Anhydrase Inhibitors: Anticonvulsant Sulfonamides Incorporating Valproyl and Other Lipophilic Moieties Bernard Masereel, † Ste ´phanie Rolin, † Francesco Abbate, ‡ Andrea Scozzafava, ‡ and Claudiu T. Supuran* ,‡,§ Department of Pharmacy, University of Namur, FUNDP, 61 rue de Bruxelles, B-5000 Namur, Belgium, Laboratorio di Chimica Inorganica e Bioinorganica, Universita ` degli Studi di Firenze, Via Gino Capponi 7, I-50121, Florence, Italy, and CSGI, c/o Universita ` degli Studi di Firenze, Via Gino Capponi 7, I-50121 Florence, Italy Received May 7, 2001 A series of aromatic/heterocyclic sulfonamides incorporating valproyl moieties were prepared to design antiepileptic compounds possessing in their structure two moieties known to induce such a pharmacological activity: valproic acid, one of the most widely used antiepileptic drugs, and the sulfonamide residue included in acetazolamide and topiramate, two carbonic anhydrase inhibitors with antiepileptic properties. Some of these derivatives showed very high inhibitory potency against three carbonic anhydrase (CA) isozymes, such as CA I, CA II, and CA IV, involved in important physiological processes. Topiramate, a recently developed antiepileptic drug possessing a sulfamate moiety, also shares this property, although earlier literature data reported this compound to be a weak-moderate CA I, II, and IV inhibitor. The valproyl derivative of acetazolamide (5-valproylamido-1,3,4-thiadiazole-2-sulfonamide, 6M) was one of the best hCA I and hCA II inhibitor in the series and exhibited very strong anticonvulsant properties in an MES test in mice. In consequence, other 1,3,4-thiadiazolesulfonamide derivatives possessing potent CA inhibitory properties and substituted with different alkyl/ arylcarboxamido/sulfonamido/ureido moieties in the 5 position have been investigated for their anticonvulsant effects in the same animal model. It was observed that some lipophilic derivatives, such as 5-benzoylamido-, 5-toluenesulfonylamido-, 5-adamantylcarboxamido-, and 5-pivaloylamido-1,3,4-thiadiazole-2-sulfonamide, show promising in vivo anticonvulsant proper- ties and that these compounds may be considered as interesting leads for developing anticonvulsant or selective cerebrovasodilator drugs. Introduction Carbonic anhydrase (CA, EC 4.2.1.1), a widely occur- ring enzyme in higher vertebrates, is also quite abun- dant in the brain, being present in the glia but not neurons, mainly as the cytosolic isozymes CA II, CA VII, and the mebrane-bound isoform CA XIV. 1-3 The func- tion of this enzyme in the brain is not well defined, but since the choroid plexus of all vertebrates has a 10 times higher concentration of CA than the eye (a tissue very rich in this enzyme) and since the cerebrospinal fluid (CSF) contains a high amount of bicarbonate, it is obvious that CAs (catalyzing with high efficiency the reversible interconversion between carbon dioxide and bicarbonate) are involved in the secretion of this fluid (as they are analogously involved in the secretion of the ocular fluid). 1-3 It has been proved that inhibition of the brain CAs causes a selective increase of the cerebral blood flow, with the concomitant raising of the carbon dioxide partial pressure. 1-4 As a consequence, CA inhibitors are useful in the treatment of conditions associated with increased intracranial pressure, 1-5 as well as different neurological/neuromuscular pathologies such as epilepsy, 1,4,6 genetic hemiplegic migraine and ataxia, 7 tardive dyskinesia, 8 hypokalemic periodic pa- ralysis, 9,10 essential tremor and Parkinson’s disease, 11 and mountain sickness, 12,13 among others. Several sulfonamide CA inhibitors such as acetazol- amide 1, 1,4 methazolamide 2, 1,4 topiramate 3, 14 and zonisamide 4 15 were and are still used as antiepileptic drugs. The anticonvulsant effects of these or related sulfonamides are probably due to CO 2 retention second- ary to inhibition of the red cell and brain enzymes, 1,4 but other mechanisms of action, such as blockade of sodium channels and kainate/AMPA receptors, as well as enhancement of GABA-ergic transmission, were also hypothesized/proved for some of these drugs. 14 Lipo- philic derivatives, such as methazolamide 2 1,4 or the tert- butoxycarbonyl derivative of acetazolamide 5 16 are more effective anticonvulsants than acetazolamide itself, proving in this way that the penetrability of the drug to brain is an important factor influencing biological activity. Acetazolamide and methazolamide are still clinically used nowadays in some forms of epilepsy, but they are considered to belong to a minor class of anti- epileptic agents. 16 The recently developed drug, topira- mate 3, is a very effective antiepileptic, 14 and it also acts as a strong CA inhibitor with a potency similar to that of acetazolamide against the physiologically important * To whom correspondence should be addressed. Phone: +39- 055-2757551. Fax: +39-055-2757555. E-mail: claudiu.supuran@ unifi.it. † University of Namur. ‡ Universita ` degli Studi di Firenze. § CSGI. 312 J. Med. Chem. 2002, 45, 312-320 10.1021/jm0109199 CCC: $22.00 © 2002 American Chemical Society Published on Web 12/19/2001