Carbonic anhydrase activators: synthesis of high affinity isozymes I, II and IV activators, derivatives of 4-(4-tosylureido-amino acyl)ethyl-1H-imidazole (histamine derivatives)

Reaction of histamine (Hst) with tetrabromophthalic anhydride and protection of its imidazole moiety with tritylsulfenyl chloride, followed by hydrazinolysis, afforded N-1-tritylsulfenyl histamine, a key intermediate which was further derivatized at its aminoethyl moiety. Reaction of the key intermediate with 4-tosylureido amino acids/dipeptides (ts-AA) in the presence of carbodiimides, afforded after deprotection of the imidazole moiety, a series of compounds with the general formula ts-AA-Hst (ts=4-MeC(6) H(4) SO(2) NHCO). Some structurally related dipeptide derivatives with the general formula ts-AA1-AA2-Hst, were also prepared, by in a similar way to the amino acyl compounds mentioned above. The new derivatives were examined as activators of three carbonic anhydrase (CA) isozymes, hCA I, hCA II (cytosolic forms) and bCA IV (membrane-bound form). Efficient activation was observed against all three isozymes, but especially against hCA I and bCA IV, with affinities in the 1-10 nanomolar range for the best compounds. hCA II was on the other hand activatable with affinities around 20-50 nM. This new class of CA activators might lead to the development of drugs/diagnostic agents for the CA deficiency syndrome, a genetic disease of bone, brain and kidneys.     

Carbonic Anhydrase Activators: Synthesis of High Affinity Isozymes I,II and IV Activators,Derivatives of 4-(Arylsulfonylureido-Amino Acyl)Ethyl-1H-Imidazole

Abstract

Based on the X-ray crystallographic structure of the adduct of human carbonic anhydrase II (hCA II) with the weak activator histamine (Briganti, F., Mangani, S., Orioli, P., Scozzafava, A., Vernaglione, G. and Supuran, C.T. (1997) Biochemistry, 36, 10 384–10 392), a novel class of tight-binding CA activators was designed by using histamine (Hst) as lead molecule. Thus, N-1-tritylsulfenyl Hst was synthesized by reaction of Hst with tetrabromophthalic anhydride followed by protection of its imidazole moiety with tritylsulfenyl chloride. After hydrazinolysis, it afforded a key intermediate which was derivatized at the aliphatic amino group. Reaction of the key intermediate with 4-fluorophenylsulfonylureido amino acids (fpu-AA) or 2-toluenesul-fonylureido amino acids (ots-AA) in the presence of carbodiimides, afforded after deprotection, a series of compounds with the general formula fpu/ots-AA-Hst (fpu = 4-FC₆H₄SO₂NHCO; ots = 2-MeC₆H₄SO₂NHCO). Some structurally related dipeptides with the general formula fpu/ ots-AA1-AA2-Hst (AA, AA1 and AA2 represent amino acyl moieties), were also prepared, by a strategy similar to that used for the simple amino acyl compounds above. The new derivatives proved to be efficient in vitro activators of three CA isozymes. Best activity was shown against hCA I and bCA IV, for which some of the new compounds (such as the Lys, Arg. His or the dipeptide derivatives) showed affinities in the 2–12 nm range (h = human; b = bovine isozymes). hCA II was on the other hand somehow less prone to activation by the new derivatives, which possessed affinities around 30–60 nM for this isozyme. Ex vivo experiments showed some of the new activators to strongly enhance red cell CA activity (180–230%) after incubation with human erythrocytes. This new class of CA activators might lead to the development of drugs/ diagnostic tools for the CA deficiency syndrome, a genetic disease of bone, brain and kidneys.     

Carbonic anhydrase activators: amino acyl/dipeptidyl histamine derivatives bind with high affinity to isozymes I, II and IV and act as efficient activators

Reaction of histamine (Hst) with tetrabromophthalic anhydride and protection of its imidazole moiety with tritylsulfenyl chloride, followed by hydrazinolysis, afforded N-1-tritylsulfenyl-histamine, a key intermediate which was further derivatized at its aminoethyl moiety. Reaction of the key intermediate with N-Boc-amino acids/dipeptides (Boc-AA) in the presence of carbodiimides afforded, after deprotection of the imidazolic and amino moieties, a series of compounds with the general formula AA-Hst (AA=amino acyl; dipeptidyl). The new derivatives were assayed as activators of three carbonic anhydrase (CA) isozymes, hCA I, hCA II (cytosolic forms) and bCA IV (membrane-bound form). Efficient activation was observed against all three isozymes, but especially against hCA I and bCA IV, with affinities in the nanomolar range for the best compounds. hCA II was, on the other hand, activatable with affinities around 10–20 nM. This new class of CA activators might lead to the development of drugs/diagnostic agents for the CA deficiency syndrome, a genetic disease of bone, brain and kidneys.     

Carbonic anhydrase activators: synthesis of high affinity isozymes I, II and IV activators, derivatives of 4-(arylsulfonylureido-amino acyl)ethyl-1H-imidazole

Based on the X-ray crystallographic structure of the adduct of human carbonic anhydrase II (hCA II) with the weak activator histamine (Briganti, F., Mangani, S., Orioli, P., Scozzafava, A., Vernaglione, G. and Supuran, C.T. (1997) Biochemistry, 36, 10,384-10,392), a novel class of tight-binding CA activators was designed by using histamine (Hst) as lead molecule. Thus, N-1-tritylsulfenyl Hst was synthesized by reaction of Hst with tetrabromophthalic anhydride followed by protection of its imidazole moiety with tritylsulfenyl chloride. After hydrazinolysis, it afforded a key intermediate which was derivatized at the aliphatic amino group. Reaction of the key intermediate with 4-fluorophenylsulfonylureido amino acids (fpu-AA) or 2-toluenesulfonylureido amino acids (ots-AA) in the presence of carbodiimides, afforded after deprotection, a series of compounds with the general formula fpu/ots-AA-Hst (fpu = 4-FC6H4SO2NHCO; ots = 2-MeC6H4SO2NHCO). Some structurally related dipeptides with the general formula fpu/ots-AA1-AA2-Hst (AA, AA1 and AA2 represent amino acyl moieties), were also prepared, by a strategy similar to that used for the simple amino acyl compounds above. The new derivatives proved to be efficient in vitro activators of three CA isozymes. Best activity was shown against hCA I and bCA IV, for which some of the new compounds (such as the Lys, Arg, His or the dipeptide derivatives) showed affinities in the 2-12 nm range (h = human; b = bovine isozymes). hCA II was on the other hand somehow less prone to activation by the new derivatives, which possessed affinities around 30-60 nM for this isozyme. Ex vivo experiments showed some of the new activators to strongly enhance red cell CA activity (180-230%) after incubation with human erythrocytes. This new class of CA activators might lead to the development of drugs/diagnostic tools for the CA deficiency syndrome, a genetic disease of bone, brain and kidneys.     

Carbonic anhydrase inhibitors: synthesis of Schiff bases of hydroxybenzaldehydes with aromatic sulfonamides and their reactions with arylsulfonyl isocyanates

Reaction of o- or p-hydroxybenzaldehydes with sulfanilamide, homosulfanilamide and p-(2-aminoethyl)- benzene-sulfonamide afforded several new Schiff bases which were subsequently derivatized at the phenolic hydroxy moiety by reaction with arylsulfonylisocyanates. The new arylsulfonylcarbamates obtained in this way possessed interesting inhibitory properties against three carbonic anhydrase (CA) isozymes, hCA I, hCA II and bCA IV (h = human, b = bovine isozyme). All these new derivatives, the simple Schiff bases and the arylsulfonylcarbamates obtained as outlined above, were more inhibitory against all isozymes as compared to the corresponding parent sulfonamide from which they were obtained. Generally, the p-hydroxybenzaldehyde derivatives were more active than the corresponding ortho isomers. An interesting behavior was evidenced for some of the ortho-substituted arylsulfonylcarbamato-sulfonamides, which showed higher affinities for the isozyme hCA I, as compared to hCA II and bCA IV (generally hCA I is 10-1000 less sensitive to "normal" sulfonamide inhibitors, such as acetazolamide, methazolamide or dorzolamide, as compared to hCA II). This make the new derivatives attractive leads for designing isozyme I-specific inhibitors.     

Carbonic Anhydrase Inhibitors. Schiff Bases of some Aromatic Sulfonamides and Their Metal Complexes: Towards More Selective Inhibitors of Carbonic Anhydrase Isozyme IV

Abstract

Reaction of three aromatic sulfonamides possessing a primary amino group, i.e., sulfanilamide, homosulfanilamide and p-aminoethyl-benzenesulfonamide with heterocyclic and aromatic aldehydes afforded a series of Schiff bases. Metal complexes of some of these Schiff bases with divalent transition ions such as Zn(II), Cu(II), Co(II) and Ni(II) have also been obtained. The new compounds were assayed as inhibitors of three isozymes of carbonic anhydrase (CA). Several of the new compounds showed a modest selectivity for the membrane-bound (bovine) isozyme CA IV (bCA IV) as compared to the cytosolic human isozymes hCA I and II, in contrast to classical inhibitors which generally possess a 17-33 times lower affinity for bCA IV. This greater selectivity toward bCA IV is due mainly to a slightly decreased potency against hCA II relative to classical inhibitors. However, metal complexes of these Schiff bases possessed an increased affinity for hCA II, being less inhibitory against bCA IV. The first type of compounds reported here (i.e., the Schiff bases of aromatic sulfonamides with heterocyclic aldehydes) might thus lead to the development of low molecular weight isozyme specific CA IV inhibitors. The difference in affinity for the three isozymes of the inhibitors reported by us here is tentatively explained on the basis of recent X-ray crystallographic studies of these isozymes and their adducts with substratesiinhibitors     

Synthesis and biological evaluation of histamine Schiff bases as carbonic anhydrase I,II, IV,VII, and IX activators

A series of 20 histamine Schiff base was synthesised by reaction of histamine, a well known carbonic anhydrase (CA, E.C 4.2.2.1.) activator pharmacophore, with substituted aldehydes. The obtained histamine Schiff bases were assayed as activators of five selected human (h) CA isozymes, the cytosolic hCA I, hCA II, and hCA VII, the membrane-anchored hCA IV and transmembrane hCA IX. Some of these compounds showed efficient activity (in the nanomolar range) against the cytosolic isoform hCA VII, which is a key CA enzyme involved in brain metabolism. Moderate activity was observed against hCA I and hCA IV (in the nanomolar to low micromolar range). The structure–activity relationship for activation of these isoforms with the new histamine Schiff bases is discussed in detail based on the nature of the aliphatic, aromatic, or heterocyclic moiety present in the aldehyde fragment of the molecule, which may participate in diverse interactions with amino acid residues at the entrance of the active site, where activators bind, and which is the most variable part among the different CA isoforms.     

Carbonic anhydrase inhibitors: SAR and X-ray crystallographic study for the interaction of sugar sulfamates/sulfamides with isozymes I,II and IV

A series of sugar sulfamate/sulfamide derivatives were prepared and assayed as inhibitors of three carbonic anhydrase (CA) isozymes, hCA I, hCA II and bCA IV. Best inhibitory properties were observed for the clinically used antiepileptic drug topiramate, which is a low nanomolar CA II inhibitor, and possesses good inhibitory properties against the other two isozymes investigated here, similarly with acetazolamide, methazolamide or dichlorophenamide. The X-ray structure of the complex of topiramate with hCA II has been solved and it revealed a very tight association of the inhibitor, with a network of seven strong hydrogen bonds fixing topiramate within the active site, in addition to the Zn(II) coordination through the ionized sulfamate moiety. Structural changes in this series of sugar derivatives led to compounds with diminished CA inhibitory properties as compared to topiramate.     

Analysis of saponins and phenolic compounds as inhibitors of α-carbonic anhydrase isoenzymes

A series of phenolic and saponin type natural products such as quercetin, rutin, catechin, epicatechin, silymarin, trojanoside H, astragaloside IV, astragaloside VIII and astrasieversianin X, were investigated for their inhibitory effects against the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1). We here report inhibitory effects of these compounds against five α-CA isozymes (hCA I, hCA II, bCA III, hCA IV and hCA VI). Most of the phenolic and saponin type compounds inhibited the isoenzymes quite effectively at low micromolar K_I-s ranging between 0.1 and 4 µM, whereas a few derivatives were ineffective (K_I-s > 100 µM). The results were remarkable which might lead to design of novel CAIs with a diverse inhibition mechanism compared to sulfonamide/sulfamate inhibitors.     

Carbonic anhydrase inhibitors: in vitro inhibition of α isoforms (hCA I,hCA II,bCA III,hCA IV) by flavonoids

A series of flavonoids, such as quercetin, catechin, apigenin, luteolin, morin, were investigated for their inhibitory effects against the metalloenzyme carbonic anhydrase (CA). The compounds were tested against four α-CA isozymes purified from human and bovine (hCA I, hCA II, bCA III, hCA IV) tissues. The four isozymes showed quite diverse inhibition profiles with these compounds. The flavonoids inhibited hCA I with K_I-s in the range of 2.2–12.8 μM, hCA II with K_I-s in the range of 0.74–6.2 μM, bCA III with K_I-s in the range of 2.2–21.3 μM, and hCA IV with inhibition constants in the range of 4.4–15.7, with an esterase assay using 4-nitrophenyl acetate as substrate. Some simple phenols/sulfonamides were also investigated as standard inhibitors. The flavonoids incorporate phenol moieties which inhibit these CAs through a diverse, not yet determined inhibition mechanism, compared to classic inhibitors such as the sulfonamide/sulfamate ones.     

α-Carbonic anhydrases are strongly activated by spinaceamine derivatives

A series of 4-substituted-spinaceamine (4,5,6,7-tetrahydro-imidazolo[4,5-c]pyridine) were prepared from histamine and aromatic aldehydes Schiff bases, and investigated as activators of four human (h) carbonic anhydrase (CA, EC 4.2.1.1) isoforms, the cytosolic hCA I, II and VII, and the membrane-associated hCA IV. All isoforms were effectively activated by the new derivatives, and the nature of the moiety in position 4 of the bicyclic system was the factor influencing activation properties against all isoforms. For hCA I, these compounds showed K_As in the range of 2.52–21.5?µM, the most effective activator being 4-(2-hydroxyphenyl)-spinaceamine. For hCA II the activation constants ranged between 0.60 and 17.2?µM, with 4-(2,3,5,6-tetrafluorophenyl)- spinaceamine the best activator. Affinity for hCA IV was in the range of 0.52–63.8?µM, and the same compound as for hCA II was the most effective activator. The most sensitive isoform for activation was the brain-associated hCA VII, for which K_As in the range of 82?nM–4.26?µM were observed. Effective hCA VII activators were the (2-bromophenyl)-, 2,3,5,6-tetrafluorophenyl- and furyl-substituted spineaceamines (K_As of 82–95?nM). As CA activators may have pharmacologic applications in various fields, this work provides interesting derivatives for further studies.     

Carbonic Anhydrase Inhibitors With Strong Topical Antiglaucoma Properties Incorporating a 4-(2-amino-pyrimidin-4-yl-amino)-benzenesulfonamide Scaffold

Reaction of 4-(2-amino-pyrimidin-4-yl-amino)-benzenesulfonamide with alkyl/aryl-sulfonyl halides, acyl halides or arysulfonyl isocyanates afforded a series of derivatives which were tested for inhibition of three carbonic anhydrase (CA) isozymes. These compounds were designed in such a way as to (i) strongly inhibit several CA isozymes involved in aqueous humor secretion within the eye (such as CA II and CA IV), and (ii) to possess a pharmacological profile that allows easy penetration through the cornea, when administered as eye drops in solution or suspension, constituting thus a valuable therapeutic approach for glaucoma. Several of the obtained inhibitors showed low nanomolar affinities for the two isozymes involved in aqueous humor secretion, CA II and CA IV. Furthermore, in normotensive and hypertensive rabbits, some of them showed an effective and prolonged intraocular pressure (IOP) lowering when administered topically, as 2% suspensions/solutions.     

Carbonic anhydrase inhibitors. Inhibition of the membrane-bound human and bovine isozymes IV with sulfonamides

An inhibition study of the human and bovine membrane-associated isozymes of carbonic anhydrase (CA, EC 4.2.1.1), hCA IV and bCA IV, with a series of sulfonamides and sulfamates, some of which are widely clinically used, such as acetazolamide, methazolamide, ethoxzolamide, topiramate, dorzolamide, dichlorophenamide, celecoxib, and valdecoxib among others, is reported. In contrast to bCA IV, which is generally strongly inhibited by most of these derivatives, hCA IV has a rather different inhibition profile. Several of these compounds such as acetazolamide, ethoxzolamide, and bromosulfanilamide are potent hCA IV inhibitors (K(i)'s of 74-93 nM), others, such as celecoxib and some halogenated sulfanilamides are medium potency inhibitors (K(i)'s of 450-880 nM) whereas most of them are weak hCA IV inhibitors (methazolamide: 6.2 microM; dorzolamide 8.5 microM; topiramate 4.9 microM; dichlorophenamide: 15.3 microM). The hCA IV/bCA IV inhibition ratios for all the investigated compounds ranged between 1.05 (for acetazolamide) and 198.37 (for dorzolamide). Based on these results, we doubt that hCA IV is indeed one of the main contributors to the intraocular pressure (IOP) lowering effects of sulfonamide CA inhibitors, in addition to hCA II, as hypothesized earlier by Maren et al. (Mol. Pharmacol.1993, 44, 901-906). Indeed, both the very good hCA IV inhibitors (acetazolamide and ethoxzolamide) as well as the quite weak hCA IV inhibitors (methazolamide, dorzolamide, or dichlorophanamide) are effective in lowering IOP when administered either systemically or topically. The membrane-associated isozyme which probably is critical for aqueous humor secretion is hCA XII and not hCA IV.     

Carbonic anhydrase inhibitors with strong topical antiglaucoma properties incorporating a 4-(2-aminopyrimidin-4-yl-amino)-benzenesulfonamide scaffold

Reaction of 4-(2-amino-pyrimidin-4-yl-amino)-benzenesulfonamide with alkyl/aryl-sulfonyl halides, acyl halides or arysulfonyl isocyanates afforded a series of derivatives which were tested for inhibition of three carbonic anhydrase (CA) isozymes. These compounds were designed in such a way as to (i) strongly inhibit several CA isozymes involved in aqueous humor secretion within the eye (such as CA II and CA IV), and (ii) to possess a pharmacological profile that allows easy penetration through the cornea, when administered as eye drops in solution or suspension, constituting thus a valuable therapeutic approach for glaucoma. Several of the obtained inhibitors showed low nanomolar affinities for the two isozymes involved in aqueous humor secretion, CA II and CA IV. Furthermore, in normotensive and hypertensive rabbits, some of them showed an effective and prolonged intraocular pressure (IOP) lowering when administered topically, as 2% suspensions/solutions.     

Carbonic anhydrase inhibitors: synthesis of sulfonamides incorporating 2,4,6-trisubstituted-pyridinium-ethylcarboxamido moieties possessing membrane-impermeability and in vivo selectivity for the membrane-bound (CA IV) versus the cytosolic (CA I and CA II) isozymes

A new approach is proposed for the selective in vivo inhibition of membrane-bound versus cytosolic carbonic anhydrase (CA, EC 4.2.1.1) isozymes with a class of positively-charged, membrane-impermeant sulfonamides. Aromatic/heterocyclic sulfonamides acting as strong (but unselective) inhibitors of this zinc enzyme were derivatized by the attachment of trisubstituted-pyridinium-ethylcarboxy moieties (obtained from 2,4,6-trisubstituted-pyrylium salts and beta-alanine) to the amino, imino, hydrazino or hydroxyl groups present in their molecules. Efficient in vitro inhibition (in the nanomolar range) was observed with some of the new derivatives against three investigated CA isozymes, i.e., hCA I, hCA II (cytosolic forms) and bCA IV (membrane-bound isozyme; h = human; b = bovine isozyme). Due to their salt-like character, the new type of inhibitors reported here, unlike the classical, clinically used compounds (such as acetazolamide, methazolamide, ethoxzolamide), are unable to penetrate biological membranes, as shown by ex vivo and in vivo perfusion experiments in rats. The level of bicarbonate excreted into the urine of the experimental animals perfused with solutions of the new and classical inhibitors suggest that: (i) when using the new type of positively-charged sulfonamides, only the membrane-bound enzyme (CA IV) was inhibited, whereas the cytosolic isozymes (CA I and II) were not affected, (ii) in the experiments in which the classical compounds (acetazolamide, benzolamide, etc.) were used, unselective inhibition of all CA isozymes (I, II and IV) occurred.     

Carbonic anhydrase inhibitors: inhibition of human and bovine isoenzymes by benzenesulphonamides,cyclitols and phenolic compounds

Carbonic anhydrase inhibitors (CAIs) are a class of pharmaceuticals used as anti-glaucoma agents, diuretics and anti-epileptics. We report here the inhibitory capacities of benzenesulphonamides, cyclitols and phenolic compounds 1–11 against three human CA isozymes (hCA I, hCA II and hCA VI) and bovine skeletal muscle carbonic anhydrase III (bCA III). The four isozymes showed quite diverse inhibition profiles with K_i values ranging from low micromolar to millimolar concentrations against all isoenzymes. Compound 5 and 6 had more powerful inhibitory action against hCA I and very similar action against hCA II and hCA VI as compared with acetazolamide (AZA) and sulphapyridine (SPD), specific CAIs. Probably the inhibition mechanism of the tested compounds is distinct of the sulphonamides with RSO₂NH₂ groups and similar to that of the coumarins/lacosamide, i.e. binding to a distinct part of the active site than that where sulphonamides bind. These data may lead to drug design campaigns of effective CAIs possessing a diverse inhibition mechanism compared to other sulphonamide/sulphamate inhibitors.     

Carbonic anhydrase I,II, IV and IX inhibition with a series of 7-amino-3,4-dihydroquinolin-2(1H)-one derivatives

A series of new derivatives was prepared by derivatisation of the 7-amino moiety present in 7-amino-3,4-dihydroquinolin-2(1H)-one, a compound investigated earlier as CAI. The derivatisation was achieved by: i) reaction with arylsulfonyl isocyanates/aryl isocyanates; (ii) reaction with fluorescein isothiocyanate; (iii) condensation with substituted benzoic acids in the presence of carbodiimides; (iv) reaction with 2,4,6-trimethyl-pyrylium tetrafluoroborate; (v) reaction with methylsulfonyl chloride and (vi) reaction with maleic anhydride. The new compounds were assayed as inhibitors of four carbonic anhydrases (CA, EC 4.2.1.1) human (h) isoforms of pharmacologic relevance, the cytosolic hCA I and II, the membrane-anchored hCA IV and the transmembrane, tumour-associated hCA IX. hCA IX was the most inhibited isoform (K_Is ranging between 243.6 and 2785.6?nm) whereas hCA IV was not inhibited by these compounds. Most derivatives were weak hCA I and II inhibitors, with few of them showing K_Is?相似文献   

Investigation of piperazines as human carbonic anhydrase I,II, IV and VII activators

Four human (h) carbonic anhydrase isoforms (CA, EC 4.2.1.1), hCA I, II, IV, and VII, were investigated for their activation profile with piperazines belonging to various classes, such as N-aryl-, N-alkyl-, N-acyl-piperazines as well as 2,4-disubstituted derivatives. As the activation mechanism involves participation of the activator in the proton shuttling between the zinc-coordinated water molecule and the external milieu, these derivatives possessing diverse basicity and different scaffolds were appropriate for being investigated as CA activators (CAAs). Most of these derivatives showed CA activating properties against hCA I, II, and VII (cytosolic isoforms) but were devoid of activity against the membrane-associated hCA IV. For hCA I, the K_As were in the range of 32.6–131?µM; for hCA II of 16.2–116?µM, and for hCA VII of 17.1–131?µM. The structure-activity relationship was intricate and not easy to rationalize, but the most effective activators were 1-(2-piperidinyl)-piperazine (K_A of 16.2?µM for hCA II), 2-benzyl-piperazine (K_A of 17.1?µM for hCA VII), and 1-(3-benzylpiperazin-1-yl)propan-1-one (K_A of 32.6?µM for hCA I). As CAAs may have interesting pharmacologic applications in cognition and for artificial tissue engineering, investigation of new classes of activators may be crucial for this relatively new research field.     

Simple methanesulfonates are hydrolyzed by the sulfatase carbonic anhydrase activity

The possible sulfatase activity of several carbonic anhydrase (CA, EC 4.2.1.1) isoforms have been investigated with a series of synthesized methanesulfonate derivatives of phenols. Four α-CA isozymes, i.e. hCA I, hCA II, hCA IV and hCA VI (h?=?human isoform), were included in the study. We evidenced that the original sulfonate esters are being hydrolyzed effectively to the corresponding phenols which there after act as CA inhibitors. The K_I-s of these compounds ranged from 10.24 to 4012 µM against hCA I, 0.10 to 35.42 µM against hCA II, 0.49 to 45.06 µM against hCA IV and 3.27 to 608 µM against CA VI, respectively. The relevant sulfatase activity of CA with these esters is amazing considering the fact that 4-nitrophenyl-sulfate, an activated ester, is not a substrate of these enzymes.     

Carbonic anhydrase activators. The selective serotonin reuptake inhibitors fluoxetine,sertraline and citalopram are strong activators of isozymes I and II

The selective serotonin reuptake inhibitors (SSRI) fluoxetine, sertraline and citalopram have been investigated for their ability to activate two carbonic anhydrase (CA) isozymes, hCA I and hCA II, in parallel with two standard activators for which the X-ray structure (in complex with isozyme II) has been resolved: histamine and phenylalanine. All three SSRI activated both isozymes with potencies comparable to that of the standards although the profile was different: for hCA I, best activators were fluoxetine and histamine, with citalopram and sertraline showing weaker activity. For hCA II, the best activators were phenylalanine and citalopram, and the weakest histamine and sertraline, whereas fluoxetine showed an intermediate behavior. These results suggest that SSRI efficacy in major depression complicating Alzheimer's disease may be partly due to their ability to activate CA isozymes and may lead to the development of potent activators for the therapy of diseases associated with significant decreases in brain CA activity.