Ординатура / Офтальмология / Английские материалы / Carbonic Anhydrase Its Inhibitors and Activators_Supuran, Scozzafava, Conway_2004

Y

4.13

SCHEME 4.2

4.9 investigated by Shepard et al. (1991) only 3-chloro-4-nitrobenzenesulfonamide easily reacted with mercaptoalcohols in an aqueous medium (in the presence of sodium acetate) or in an alcoholic medium (EtOH and Et3N), the substitution reaction being facilitated by the labilizing effect of the nitro group in the ortho position to the halogeno-moiety leaving group. Furthermore, in this unique case, it was not necessary to protect the SO2NH2 group.

Compounds 4.13 prepared by this approach (Table 4.3) were highly active CAIs. The inhibitory potency increased with the increase in the length of the alkyl chain from 2 to 5 carbon atoms. Without exception, sulfones were more potent inhibitors than were the corresponding sulfides, a phenomenon that can be correlated with the decrease of pKa of the SO2NH2 protons by hydroxyalkylsulfonyl moieties (as compared to hydroxyalkylthio groups). Table 4.3 also gives the pKa values for these sulfonamides. The presence of fluorine or chlorine atoms in position 3 of the benzene nucleus generally led to stronger CAIs, whereas moieties such as COOH and COOMe led to less potent inhibitors. Groups such as NO2 or NH2 in this position also led to active compounds (Shepard et al. 1991).

Shepard et al. (1991) also prepared 2-chloro-5-fluoro-4-substitued-benzene- sulfonamides of types 4.16 and 4.17 according to the strategy presented in Scheme 4.3. By treating 2-fluoro-5-chlorotoluene 4.14 with bromine in homolytic conditions, followed by reacting with sodium diethylmalonate, deprotecting the monocarboxylic acid, and reducing its ester, the hydroxypropyl derivative 4.15 was obtained, which was acetylated, chlorosulfonated and amidated. Sulfonamides 4.16 and 4.17 prepared by this procedure showed IC50 values ca. 2 nM against hCA II, being potent CAIs, similar to the compounds 4.13 (Shepard et al. 1991).

Boddy et al. (1989) investigated erythrocyte CA inhibition with the salicylic acid derivatives 4.18. These compounds were prepared by reacting phenyl salicylate with

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TABLE 4.3

CA II Inhibition with Aromatic

Sulfonamides 4.13 and Their pKa Values

Source: From Shepard, K.L. et al. (1991) Journal of

Medicinal Chemistry 34, 3098–3105. With permission.

sulfanilamide (n = 0) and homosulfanilamide (n = 1). The compounds strongly inhibit human red cell CA (with KIs of 53 and 98 nM, respectively), probably because they are stronger acids than the parent unacylated sulfonamides. The same authors studied the binding to erythrocytes of these CAIs compared with that of compounds possessing –SO2NHMe and –SO2NH-2-pyridyl groups (which are not CAIs). The unsubstituted sulfonamides 4.18 strongly bound to red cells, with affinities 10 to 100 times higher than the substituted derivatives incorporating N-modified sulfonamide moieties, whereas their affinities for CA were also 100 to 1000 times higher.

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N

H

4.18 n = 0,1

Another approach used to prepare CA inhibitors from this class involved Schiff bases of aromatic sulfonamides, such as 4.19 and 4.20. Derivative 4.19 was prepared from sulfanilamide and salicyl aldehyde, whereas 4.20, from 4-sulfamoyl-benzalde- hyde and substituted anilines, had already been reported by Beasley et al. (1958). This class of CAIs was subsequently extensively investigated by our group (Supuran et al. 1996b, 1996c, 1997b; Popescu et al. 1999; Scozzafava et al. 2000a). Initially, a large series of sulfanilamide-derived Schiff bases of type 4.21, which incorporated a large number of aromatic and heterocyclic moieties (arising from the aldehyde component of the condensation), was prepared (Supuran et al. 1996a). These compounds were potent CAIs and also showed more affinity for the membrane-bound (CA IV) than the cytosolic (CA I and CA II) isozymes. The related derivatives 4.22 and 4.23, prepared from aromatic/heterocyclic sulfonamides and chalcones (Supuran et al. 1996c), showed the same interesting biological activities, being generally more potent CA IV than CA I/II inhibitors. Even stronger CAIs were then reported, which

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For 4.25 and 4.26: OH and bulky substituents in ortho and para; X = p -F-, p -CI-, p-Me- and o-Me.

incorporated homosulfanilamide, p-aminoethylbenzenesulfonamide and different aromatic/heterocyclic aldehyde moieties of types 4.24 to 4.26 (Popescu et al. 1999; Scozzafava et al. 2000a). Many of these compounds showed affinities in the low nanomolar range for the physiologically relevant isozymes CA I, II and IV, with a slightly higher affinity for CA IV as compared to that for the cytosolic isozymes.

It is worth noting that though the compound saccharin 4.27 has a substituted sulfonamido group, Supuran and Banciu (1991) showed that it acts as a weak CAI (IC50 = 97 μM against hCA II). It is not known whether this has physiological consequences in humans.

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The reaction of 4-carboxy-benzenesulfonamide 4.28 or 4-chloro-3-sulfamoyl benzoic acid 4.29 with carboxy-protected amino acids/dipeptides, or aromatic/heterocyclic sulfonamides/mercaptans afforded the corresponding benzene-carboxam- ide derivatives 4.30 and 4.31 (Table 4.4; Mincione et al. 2001). These amides were tested as inhibitors of three isozymes, CAs I, II and IV. Some of the new derivatives showed affinity in the low nanomolar range for isozymes CA II and CA IV, which are involved in aqueous humor secretion within the eye and were tested as topically acting antiglaucoma agents in normotensive and glaucomatous rabbits. Good in vivo activity and prolonged duration of action have been observed for some of these derivatives, whereas some of the 4-chloro-3-sulfamoyl benzenecarboxamides 4.31 showed higher affinity for CA I than for the sulfonamide avid isozyme CA II.

Carboxamides structurally related to 4.30 were also reported by several other groups. Whitesides’ group reported derivatives of 4-carboxy-benzenesulfonamide to which oligopeptidyl moieties were attached of type 4.32 (Jain et al. 1994; Boriack et al. 1995) and 4.33 (Avila et al. 1993; Gao et al. 1995). In another series of such derivatives, oligoethylene glycol units were attached to 4-carboxy-benzenesulfona- mide and the terminal hydroxy moiety of the tail was derivatized by acyl amino moieties. [Six derivatives of type 4.34 were thus obtained by Gao et al. (1996).] Finally, Baldwin’s group reported several structurally related inhibitors of type 4.35, obtained again from 4-carboxy-benzenesulfonamide by attaching peptidyl moieties incorporating nipecotic acid at its carboxy group (Burbaum et al. 1995).

Jain’s group reported carboxamides of type 4.36, incorporating fluoro-substituted anilines (Doyon and Jain 1999). Some of these derivatives showed very good hCA II inhibitory properties.

Casini et al. (2000) reported an alternative approach for obtaining water-soluble, potent CAIs with putative applications as agents used to treat ocular hypertension and glaucoma. Thus, 4-isothiocyanato-benzenesulfonamide 4.37, obtained from sulfanilamide 4.1 and thiophosgene (Scheme 4.4), was reacted with many amines, amino acids or oligopeptides, and the thioureas 4.38 thus obtained showed excellent CA inhibitory properties against isozymes I, II and IV (Table 4.5) and water solubilities either as sodium salts (for the amino acid/ologopeptide derivatives) or as hydrochlorides/triflates (in the case of the amine derivatives). The nucleophiles used in the syntheses were chosen such that they had pKa values in the physiological range. More precisely, salts of these new inhibitors applied in the eyes of experimental animals generally possessed pH values in the range of 6.5 to 7.0. Such salts were applied topically in the eyes of normotensive or glaucomatous rabbits and produced a powerful, long-lasting reduction of intraocular pressure (IOP).

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TABLE 4.4

Inhibition Data for Benzene-Carboxamide Derivatives 4.30 and 4.31

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TABLE 4.4 (continued)

Inhibition Data for Benzene-Carboxamide Derivatives 4.30 and 4.31

aHuman (cloned) isozymes.

bFrom bovine lung microsomes by the esterase method.

Source: From Mincione, F. et al. (2001) Bioorganic and Medicinal Chemistry Letters 11, 1787–1791. With permission.

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4.35: R = i -Pr-CH2; HOOCCH2; H2NCOCH2CH2

4.2.2 HETEROCYCLIC SULFONAMIDES

Investigation of heterocyclic sulfonamides as CAIs has been fostered by the discovery of Davenport (1945) that thiophene-2-sulfonamide is 40 times more active than sulfanilamide as a CAI. Shortly thereafter, in a classical work, Roblin’s group prepared a very large series of heterocyclic sulfonamides derived from the most important ring systems (imidazole, alkyland aryl imidazoles, benzimidazoles, benzothiazole,

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SO2NH2

SCHEME 4.4

1,2,4-triazole, thiazole, tetrazole and alkyl/aryl tetrazoles, 1,3,4-thiadiazole, pyrimidine, pyrazine, etc.; Roblin and Clapp 1950; Miller et al. 1950).

Two strategies were used to prepare such derivatives: (1) sulfonation/chlorosulfonation of the heterocyclic compound (RH in Scheme 4.5), followed by transformation of the sulfonic acid 4.39 into the sulfonyl chloride 4.40 and subsequent amidation with formation of the desired sulfonamide 4.42; and (2) oxidative chlorination of heterocyclic mercaptans 4.41 (generally in acetic acid as a solvent), followed by amidation of the sulfonyl chloride generated this way (Scheme 4.5) and formation of the desired heterocyclic sulfonamide 4.42.

The second approach has largely been applied to the preparation of heterocyclic sulfonamides, due to the fact that either sulfonation/chlorosulfonation cannot be always carried out successfully for most heterocycles or because heterocyclic mercaptans are easily prepared by a variety of methods, the sulfonyl chlorides are generally obtained in very good yields and the amidation of sulfonyl chlorides 4.40 occurs in quantitative yield (Roblin and Clapp 1950; Miller et al. 1950). The large number of compounds prepared in the classical studies of Roblin’s group helped establish two important facts connecting chemical structure with CA inhibitory action: (1) five-membered derivatives were more effective CAIs than six-membered ring compounds, and (2) the presence of nitrogen and sulfur atoms within the ring led to the most potent inhibitors. Thus, extremely powerful inhibitors were found to be 5-substituted-1,3,4-thiadiazole-2-sulfonamides 4.43 (R = NH2) and 4.44 (R = NHAc), benzothiazole-2-sulfonamide 4.45, as well as 1,3,4-thiadiazoline-sulfonamides

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TABLE 4.5

CA Inhibition Data with 4-Isothiocyanatobenzenesulfonamide 4.37 and the Thioureas 4.38

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