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

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FIGURE 6.6 Crystal structure of [Co(macm)(NH3)(aib)2(NO3)2] ◊ 2H2O (6.7). (Reprinted from Alzuet, G. et al. (1993b) Inorganica Chimica Acta 205, 79–84. With permission from Elsevier.)

FIGURE 6.7 Crystal structure of [Zn(macm)2(NH3)2] (6.8). (Reprinted from Alzuet, G. et al. (1995) Journal of Inorganic Biochemistry 57, 219–234. With permission from Elsevier.)

as a spectroscopic model for the binding of inhibitors to Co(II)-substituted CA (Alzuet et al. 1995).

The compounds [M(macm)2(py)2(OH2)2] (M = Cu, Co, Ni; 6.9, 6.10, 6.11; Figure 6.8) were reported to be octahedral (Alzuet et al. 1992). Methazolamide behaves again as a monodentate ligand, binding to the metal ion through the sulfonamidate nitrogen atom. Deprotonated methazolamide ligands occupy equatorial sites in a trans geometry in these compounds.

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FIGURE 6.8 Crystal structure of [Ni(macm)2(py)2(OH2)2] (6.9). (Reprinted from Alzuet, G. et al. (1992) Polyhedron 22, 2849–2856. With permission from Elsevier.)

In all these complexes, one relevant feature of methazolamide is the shortening of the sulfonamide S–N distance and the opposite lengthening of the contiguous S–C bond distance. The shortening of the S–N bond distance depends on the nature of the metal ion. The minor S–N bond length reduction was observed for the Co(III)–macm complex with respect to other M(II)–macm complexes, and it might be related to the trivalent nature of the metal center.

6.4 BENZOLAMIDE COMPLEXES

Benzolamide [(5-phenylsulfonamido-1,3,4-thiadiazole-2-sulfonamide), H2bz] contains two dissociable protons similar to those in acetazolamide, incorporating multiple potential donor binding sites at the thiadiazole and the two sulfonamide moieties (Alzuet et al. 1998, 1999). Hence, as for acetazolamide, a multitude of coordination possibilities is expected (Scheme 6.3).

Our group reported ternary zinc and copper benzolamide complexes with amines [ammonia, diethylenetriamine (dien), dipropylenetriamine (dipt)] and the tripodal ligand tris(2-benzimidazolyl-methylamine) (L) (Alzuet et al. 1999). In these complexes, the coordination behavior of benzolamide was found to be different (Table 6.5).

In the first reported benzolamide complex [Cu(bz)(NH3)4] (6.12; Figure 6.9) for which the x-ray structure was determined, the coordination behavior of benzolamide is unexpected (Alzuet et al. 1998). Although dideprotonated, it acts as a monodentate ligand via the nitrogen atom of the primary sulfonamido group. This fact contrasts with the ligand behavior of acetazolamide (H2 acm) in the analogous [Cu(acm)(NH3)2(H2O)]2 ◊ 2H2O complex (Ferrer et al. 1990b), in which the doubly

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SCHEME 6.3

TABLE 6.5

Benzolamide Complexes with Structures Determined by x-Ray Crystallography

ionized acetazolamide coordinates through the N(sulfonamido) and N(thiadiazole) atoms. The reason for the different behaviors of the two sulfonamides can be inferred from the stronger interaction between the thiadiazole ring and the acetamido group

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FIGURE 6.9 Crystal structure of [Cu(bz)(NH3)4] (6.12). (Reprinted from Alzuet, G. et al. (1998) Inorganica Chimica Acta 273, 334–338. With permission from Elsevier.)

Alzuet, G. et al. (1999) Journal of Inorganic Biochemistry 75, 189–198. With permission from Elsevier.)

in acm2– as compared to that of the thiadiazole ring and the sulfonamido group in bz2–. From spectroscopic data, a similar coordination behavior has been proposed for the compounds [Cu(bz)(dien)(OH2)] and [Cu(bz)(dipn)(OH2)] (Alzuet et al. 2000).

The reaction of benzolamide, ammonia and Zn(II) led to the formation of {[Zn2(bz)2(NH3)4] ◊ H2O}• (6.13; Alzuet et al. 1999; Figure 6.10). In this case, the dianion of benzolamide acts as a bridge linking two metal centers through the nitrogen atom of the primary sulfonamido group and the thiadiazole nitrogen N(3). The structure consists of infinite chains linked together by hydrogens bonds. A similar polymeric structure was proposed for the (Hyt)Zn(NH3)2 compound described by Hartmann and Vahrenkamp (1994), where Hyt stands for the dideprotonated form of the bis-sulfonamide ligand hydrochlorothiazide. The Zn–N-sulfonamide bond

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FIGURE 6.11 Crystal structure of [Zn(Hbz)L]ClO4.H2O (6.14) [L = tris (2-benzimidazolyl- methylamine)]. (Reprinted from Alzuet, G. et al. (1999) Journal of Inorganic Biochemistry 75, 189–198. With permission from Elsevier.)

length of 1.978 Å compares well with that found in the acetazolamide–hCAII complex (1.90 Å). The Zn(II) ion adopts a nearly regular tetrahedral geometry with N–Zn–N angles ranging from 106.6 to 112.2º. These angles are close to those reported by Vidgren et al. (1990) for the Zn(II) tetrahedron in the acetazola- mide–hCAII complex (N-sulfonamide–Zn–N–His94/119, 104º and 113º, respectively). Furthermore, this structure is reminiscent of those of [Zn(Hacm)2(NH3)2] (Ferrer et al. 1987; Hartmann and Vahrenkamp 1991) and [Zn(macm)2(NH3)2] (Alzuet et al. 1995), which are structural models of the sulfonamide interaction with the Zn(II) ion at the active site of CA.

For the synthesis of Zn-benzolamide complexes, a tripodal tris-benzimidazole ligand [tris(2-benzimidazolyl-methylamine) (L)] has been used, with the aim of mimicking the environment of the metal center in CA (Alzuet et al. 1999). The complex [Zn(Hbz)L](ClO4) ◊ H2O (6.14; Figure 6.11) has been obtained, which consists of cationic [Zn(Hbz)L]+ entities and no coordinating ClO4– anions. The benzolamide anion interacts through the thiadiazole nitrogen atom contiguous to the deprotonated sulfonamido group. Angles around the Zn(II) ion show a distorted trigonal bipyramidal geometry.

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FIGURE 6.12 Crystal structure of [Zn(Hbz)2(dien)] (6.16). (Reprinted from Alzuet, G. et al. (2000) Polyhedron 19, 725–730. With permission from Elsevier.)

An interesting aspect is the different coordination behaviors exhibited by benzolamide and the closely related sulfonamide acetazolamide toward Zn(II) when these sulfonamides are monodeprotonated. Although both sulfonamides have the same potential donor atoms, acetazolamide interacts through the sulfonamide nitrogen atom in the [Zn(Hacm)2(NH3)2] compound (Ferrer et al. 1987; Hartmann and Vahrenkamp 1991) whereas benzolamide coordinates through a thiadiazole nitrogen atom in the [Zn(Hbz)L](ClO4)◊H2O complex.

The ternary complexes [M(Hbz)2(dien)] (6.15, 6.16; M = Cu, Zn; Alzuet et al. 2000) were obtained by reacting the metal salt, the triamine and benzolamide in a molar ratio of 1:1:2. The ratio of reagents is important for obtaining these compounds, because addition of an equimolecular amount of triamine and benzolamide leads to the formation of the previously reported M(bz)(dien)(H2O) (M = Cu, Zn) compounds, in which the benzolamide is present in the dideprotonated form.

In the [Cu(Hbz)2(dien)] and [Zn(Hbz)2(dien)] complexes (Figure 6.12), the metal ion is pentacoordinated by five nitrogen atoms, the structure being best described as a regular square pyramid. Both MN5 chromophores are essentially square pyramidal, but with significant differences in the local molecular stereochemistry. For these two structures, the major changes in the angles surrounding the metal center are found in the N(5)-M-N(7) and N(6)-M-N(3), which expands from 149.8 and 153.4º [Zn(Hbz)2(dien)] to 163.4 and 162.3º [Cu(Hbz)2(dien)].

In these complexes, the coordination mode of benzolamide is determined by the deprotonation occurring at the secondary sulfonamide moiety. This makes the thiadiazole nitrogen closest to this sulfonamido group, N(3), the best donor atom. Structural determinations of all these complexes have demonstrated the coordinative

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versatility of benzolamide, a feature that it shares with acetazolamide. Although it is difficult to rationalize the coordination behavior of this ligand, our investigations have indicated that in the monodeprotonated form benzolamide behaves as a monodentate ligand coordinating the metal through the thiadiazole nitrogen atom closest to the substituted sulfonamido group, (N3). When dideprotonated, benzolamide shows a more variable coordination behavior, acting either as a bridge through the thiadiazole and free sulfonamido nitrogen atoms or as a monodentate ligand via the primary sulfonamido nitrogen. A comparison of the structures of the {[Zn2(bz)2(NH3)4]◊2H2O}• and [Cu(bz)(NH3)4] complexes indicates that the coordination mode of benzolamide, when doubly ionized, depends on the nature of the metal ion. A metal ion dependence has also been reported (Coleman 1975) for the binding of sulfonamides to Zn(II)- and Co(II)-substituted CAs. Furthermore, our results indicate that benzolamide interacts with Zn(II) through the sulfonamido nitrogen atom as a dinegative anion, so that only in this case this interaction can be considered as a model for the binding of the sulfonamide to the metal center within the CA active site.

6.5COMPLEXES CONTAINING OTHER SULFONAMIDE CAIs

Besides metal complexes of acetazolamide, methazolamide and benzolamide, Supuran`s group prepared numerous metal complexes of other sulfonamides, such as ethoxzolamide (HEZA) or acetazolamide congeners incorporating other moieties in the 5-position of the thiadiazole ring, of types 6.20 to 6.25 (Andruh et al. 1991; Supuran et al. 1991, 1993a,b; Supuran 1992, 1995a, 1998a, 1998b, 1999; Almajan and Supuran 1997; Jitianu et al. 1997; Scozzafava et al. 2001, 2002; Briganti et al. 2000).

Ethoxzolamide 6.17 was shown to behave as a bidentate ligand in both the anion

and the neutral form, binding the metal ions through the Nsulfonamide and the benzothiazole nitrogen atoms (Andruh et al. 1991; Supuran et al. 1991). However, no

crystal structures of ethoxzolamide complexes have been reported so far. The thienothiopyran sulfonamides dorzolamide 6.18 and MK-907 6.19 (the first is a topically acting antiglaucoma agent in clinical use, and the second was a clinical candidate before dorzolamide; Supuran et al. 2003) have also been investigated for their complexation behavior (Supuran 1995b, 1996). These sulfonamides were shown to

behave as bidentate ligands through the Nsulfonamide and the Sheterocyclic atoms (Supuran 1995b, 1996). Many complexes of diand trivalent metal ions incorporating the

various 1,3,4-thiadiazole-sulfonamides of types 6.20 to 6.25 were reported and assayed as CAIs against the major isozymes CA I and CA II (Supuran 1992, 1995a, 1998a, 1998b, 1999; Almajan and Supuran 1997; Jitianu et al. 1997; Scozzafava et al. 2001, 2002; Briganti et al. 2000). According to the IR spectra of these complexes, and taking into account the ligand behavior of acetazolamide and benzolamide discussed earlier, it has been proposed that these ligands bind metal ions through the Nsulfonamide and the Nthiadiazole atoms in a bidentate fashion (Supuran 1992,

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1995a, 1998a, 1998b, 1999; Almajan and Supuran 1997; Jitianu et al. 1997; Scozzafava et al. 2001, 2002; Briganti et al. 2000).

Borja et al. (1998) described the crystal structure of [Zn(ats)2(NH3)] ◊ H2O, where Hats is 5-amino-1,3,4-thiadiazole-2-sulfonamide 6.26 (the acetazolamide precursor). In this complex, the sulfonamide deprotonated ligand ats acts as a bridge between

two Zn ions, binding them through the Nsulfonamide and the Nthiadiazole atoms. Later, Chufan et al. (2001) reported the crystal structures of [Cu(ats–)2(dipn)] and

[Ni(dien)2](ats–)Cl ◊ H2O (dipn = dipropylentriamine; dien = diethylenediamine). In the latter complex, ats acts as a counterion. Pedregosa et al. (1995) also reported the crystal structure of the [Cu(B-ats–)(NH3)2]2 complex, where B-ats– is the anion of the 5-tertbutyloxycarbonylamido-1,3,4-thiadiazole-2-sulfonamide 6.27. This ligand

behaves as a bidentate ligand through the Nsulfonamide and the Nthiadiazole.

Scozzafava et al. (2001, 2002) have reported water-soluble metal complexes of sulfonamides incorporating polyamino-polycarboxylate tails of types 6.28 and 6.29 (as well as many congeners with tails other than those of EDTA and DTPA shown in these structures). It has been hypothesized that such sulfonamides behave as

ligands coordinating the metal ion through the Ocarboxylate moieties of the polyaminopolycarboxylate tails, without the involvement of the sulfonamide moieties in the

complexation, but no crystal structures of such derivatives are available at present.

HOOC

SCHEME 6.4

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Sumalan et al. (1996) described the crystal structure of the [Zn(sa)(NH3)] ◊ NH3 complex ([sa– = anion of the 8-quinolinsulfonamide 6.30]). The ligand binds the metal ion bidentately through the N(sulfonamide) and the N(quinoline) atoms.

6.6APPLICATIONS OF METAL COMPLEXES OF SULFONAMIDES IN THERAPY

The CA inhibitory properties of numerous metal sulfonamide complexes mentioned here have been investigated in detail, mostly against the red cell isozymes hCA I and hCA II, but in some cases also against the membrane-bound isozyme bCA IV (h = human, b = bovine isozyme; reviewed in Alzuet et al. 1994c and Supuran 1994). Such studies surprisingly indicated that the metal complexes are 10 to 100 times more potent inhibitors of these isozymes as compared to the corresponding parent sulfonamides, making them among the most potent CAIs ever reported, with inhibition constants in the low nanomolar–picomolar range (Alzuet et al. 1994c; Supuran 1994). It is believed that this powerful inhibition is due to a dual mechanism of action of the complexes, through sulfonamide anions and metal ions obtained in dilute solution by dissociation of the coordination compounds (Luca et al. 1991). Sulfonamidate anions formed this way then bind to the Zn(II) ion within the enzyme active site, whereas the metal ions block the proton shuttle residues of CA, for instance His 64 for hCA II (Alzuet et al. 1994c; Supuran 1994; Supuran et al. 2003).

As a consequence of these very powerful enzyme inhibitory properties, several interesting applications have been reported for some metal complexes of heterocyclic sulfonamides possessing strong CA inhibitory properties. Thus, some Zn(II) and Cu(II) complexes of heterocyclic sulfonamides of type 6.20 to 6.25 and 6.28, 6.29 were very efficient intraocular pressure (IOP) lowering agents when administered topically in normotensive or glaucomatous rabbits, although most of the parent sulfonamides from which they were obtained do not show topical antiglaucoma activity (Supuran et al. 1998a, 1999; Briganti et al. 2000; Scozzafava et al. 2001, 2002). The observed topical activity has been explained by a modulation by the metal ion on the physicochemical properties of the complex, which in some cases becomes more polar and thus penetrates better though the cornea to inhibit ciliary processes CAs, thereby reducing elevated IOP in animal models of glaucoma (Supuran et al. 1998a, 1999; Briganti et al. 2000; Scozzafava et al. 2001, 2002).

Some Al(III) complexes, such as the benzolamide complex, act as efficient antisecretory agents in dogs. It has been proposed that the Zn(II), Mg(II) and Al(III) sulfonamide complexes might constitute a new class of antiulcer agents (Scozzafava et al. 2000).

It has been reported that copper(II) complexes of acetazolamide and methazolamide are potent anticonvulsant agents. Their activity is higher than that shown by the parent sulfonamides (Alzuet et al. 1994b).

Mastrolorenzo et al. (2000a, 2000b) reported that some silver(I) complexes of sulfonamide CAIs, structurally related to acetazolamide and benzolamide (possessing potent CA inhibitory properties), also show very strong antifungal properties, explaining the use of such pharmacological agents for the treatment of burns.

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All these data show that the metal complexes of sulfonamide CAIs have a largely unexplored potential for the design of pharmacological agents with a host of biological activities. By choosing different metal ions and diverse sulfonamides, it is possible to fine tune the biological activity in a manner rarely attainable by other classical techniques of drug design.

REFERENCES

Almajan, L.G., and Supuran, C.T. (1997) Carbonic anhydrase inhibitors. Part 30. Complexes of 5-pivaloylamido-1,3,4-thiadiazole-2-sulfonamide with trivalent metal ions. Revue Roumaine de Chimie 42, 593–597.

Alzuet, G., Casanova, J., Borrás, J., García Granda, S., Gutiérrez-Rodríguez, A., and Supuran, C.T. (1998) Copper complexes modelling the interaction between benzolamide and Cu-substituted carbonic anhydrase: Crystal structure of Cu(bz)(NH3)4 complex. Inorganica Chimica Acta 273, 334–338.

Alzuet, G., Casanova, J., Ramírez, J.A, Borrás, J., and Carugo O. (1995) Metal complexes of the carbonic anhydrase inhibitor methazolamide: Crystal structure of the Zn(macm)2(NH3)2. Anticonvulsant properties of Cu(macm)2(NH3)3(H2O). Journal of Inorganic Biochemistry 57, 219–234.

Alzuet, G., Casella, L., Perotti A., and Borrás, J. (1994a) Acetazolamide binding to Zn(II), Co(II) and Cu(II) Model complexes of carbonic anhydrase. Journal of the Chemical Society — Dalton Transactions, 2347–2351.

Alzuet, G., Ferrer, S., and Borrás, J. (1991) Acetazolamide-M(II) [M(II) = Co(II), Ni(II) and Cu(II)] complexes with ethylamine, diethylamine, triethylamine and potassium hydroxide. Journal of Inorganic Biochemistry 42, 79–86.

Alzuet, G., Ferrer, S., Borrás, J., Castiñeiras, A., Solans, X., and Font-Bardía M. (1992) Coordination compounds of methazolamide: Synthesis, spectroscopic studies and crystal Structures of [M(macm)2(py)2(OH2)2] [M=Co(II), Ni(II) and Cu(II)]. Polyhedron 22, 2849–2856.

Alzuet, G., Ferrer, S., Borrás, J., Solans, X., and Font-Bardía, M. (1993a) Coordination behaviour of methazolamide [N(-4-methyl-2-sulfamoyl- 2-1,3,4-thiadiazolin-5- ylidene)] acetamide, an inhibitor of carbonic anhydrase enzyme: Synthesis, crystal structure and properties of bi(methazolamidate)tetrammine nickel (II). Inorganica Chimica Acta 203, 257–261.

Alzuet, G., Ferrer, S., Borrás, J., and Sorenson, J.R.J. (1994b) Anticonvulsant properties of copper acetazolamide complexes. Journal of Inorganic Biochemistry 55, 147–151.

Alzuet, G., Ferrer, S., Borrás, J., and Supuran C.T. (1994c) Complexes of heterocyclic sulfonamides: A class of potent, dual carbonic anhydrase inhibitors. Romanian Chemical Quarterly Reviews 2, 283–300.

Alzuet, G., Ferrer, S., Casanova, J., Borrás, J., and Castiñeiras, A. (1993b) A Co(III) complex of carbonic anhydrase inhibitor methazolamide and the amino-imino “aib” ligand formed by reaction of acetone and ammonia. Inorganica Chimica Acta 205, 79–84.

Alzuet, G., Ferrer-Llusar, S., Borrás, J., and Martínez-Mánez, R. (2000) New Cu(II) and Zn(II) complexes of benzolamide with diethylentriamine: synthesis, spectroscopy and x-ray structures. Polyhedron 19, 725–730.

Alzuet, G., Ferrer-Llusar, S., Borrás, J., Server-Carrio, J., and Martínez-Mánez, R. (1999) Co-ordinative versatility of the carbonic anhydrase inhibitor benzolamide in zinc and copper model compounds. Journal of Inorganic Biochemistry 75, 189–198.

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