Carbonic anhydrase inhibitors: Synthesis and inhibition of the human carbonic anhydrase isoforms I,II, VII,IX and XII with benzene sulfonamides incorporating 4,5,6,7-tetrabromophthalimide moiety

A series of 4,5,6,7-tetrabromo-1,3-dioxoisoindolin-2-yl benzenesulfonamide derivatives (compounds 1–8) was synthesized by reaction of benzene sulfonamide derivatives with 4,5,6,7-tetrabromophthalic anhydride moiety. These new sulfonamides were investigated as inhibitors of the zinc metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1) and more specifically against the human (h) cytosolic isoforms hCA I, II and VII and the transmembrane tumor-associated isoform hCA IX and XII. The new compounds were good hCA I inhibitors (Kis in the range of 143 to >10,000 nM), but were moderately effective, as hCA II inhibitors (Kis of 47–190 nM) and poor hCA VII inhibitors (Kis in the range of 54–175 nM) compared to acetazolamide. The tumor-associated hCA IX was effectively inhibited with Kis ranging between 8.5 and 234 nM and hCA XII with inhibition constants in the range of 6.1–197 nM with high selectivity ratio. The structure–activity relationship (SAR) with this series of sulfonamides is straightforward, with the main features leading to good activity for each isoforms being established. The high sequence hCA alignment homology and molecular docking study of compounds was performed to rationalize the SAR reported over here.     

Carbonic anhydrase inhibitors: Synthesis and inhibition of the human carbonic anhydrase isoforms I,II, IX and XII with benzene sulfonamides incorporating 4- and 3-nitrophthalimide moieties

A series of 4 and 5 nitro-1,3-dioxoisoindolin-2-yl benzenesulfonamide derivatives (compounds 1–8) was synthesized by reaction of benzenesulfonamide derivatives with 4 and 3-nitrophthalic anhydrides. These new sulfonamides were investigated as inhibitors of the zinc metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1) and more specifically against the human (h) cytosolic isoforms hCA I and II and the transmembrane, tumor-associated hCA IX and XII. Most of the novel compounds were medium potency-weak hCA I inhibitors (K_is in the range of 295–10,000 nM), but were more effective hCA II inhibitors (K_is of 1.7–887 nM). The tumor-associated hCA IX was also inhibited, with K_is in the micromolar range, whereas against hCA XII the inhibition constants were in the range of 90–3746 nM. The structure–activity relationship (SAR) with this series of sulfonamides is straightforward, with the main features leading to good activity for each isoforms being established. The high sequence hCA alignment homology and molecular docking studies was performed in order to rationalize the activities reported and binding mode to different hCA as inhibitors.     

Carbonic anhydrase inhibitors. Phenacetyl-, pyridylacetyl- and thienylacetyl-substituted aromatic sulfonamides act as potent and selective isoform VII inhibitors

A series of aromatic/heterocyclic sulfonamides incorporating phenyl(alkyl), halogenosubstituted-phenyl- or 1,3,4-thiadiazole-sulfonamide moieties and thienylacetamido; phenacetamido- and pyridinylacetamido tails were prepared and assayed as inhibitors of cytosolic human carbonic anhydrase (hCA, EC 4.2.1.1) isoforms hCA I, II and VII. The new compounds showed moderate inhibition of the two ubiquitous isoforms I and II (K_Is of 50–390 nM) and excellent inhibitory activity against the brain associated hCA VII (K_Is in the range of 4.7–8.5 nM). Isoform VII highly selective inhibitors are being detected for the first time, with selectivity ratios for inhibiting CA VII over CA II of 11–75, and for inhibiting CA VII over CA I of 10–49, which may be useful for understanding the role of CA VII in epileptogenesis and other physiologic processes.     

Synthesis of novel acridine and bis acridine sulfonamides with effective inhibitory activity against the cytosolic carbonic anhydrase isoforms II and VII

4-Amino-N-(4-sulfamoylphenyl)benzamide was synthesized by reduction of 4-nitro-N-(4-sulfamoylphenyl)benzamide and used to synthesize novel acridine sulfonamide compounds, by a coupling reaction with cyclic-1,3-diketones and aromatic aldehydes. The new compounds were investigated as inhibitors of the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1), and more precisely the cytosolic isoforms hCA I, II and VII. hCA I was inhibited in the micromolar range by the new compounds (K_Is of 0.16–9.64 μM) whereas hCA II and VII showed higher affinity for these compounds, with K_Is in the range of 15–96 nM for hCA II, and of 4–498 nM for hCA VII. The structure–activity relationships for the inhibition of these isoforms with the acridine–sulfonamides reported here were also elucidated.     

Substituted benzene sulfonamides incorporating 1,3,5-triazinyl moieties potently inhibit human carbonic anhydrases II,IX and XII

A series of benzene sulfonamides incorporating 1,3,5-triazinyl moieties were synthesized using cyanuric chloride as starting material. Inhibition studies against human carbonic anhydrase (hCA, EC 4.2.1.1) isoforms I, II (cytosolic) and IX, XII (transmembrane, tumor-associated) isoforms were performed with the new compounds. hCA I was modestly inhibited (K_Is in the range of 87 nM–4.35 μM), hCA II was moderately inhibited by most of the new compounds (K_Is in the range of 12.5–130 nM), whereas the tumor associated isoforms were potently inhibited, with K_Is in the range of 1.2–34.1 nM against hCA IX and of 2.1–33.9 against hCA XII, respectively. Docking studies of some of the new compounds showed an effective binding mode within the enzyme active site, as demonstrated earlier by X-ray crystallography for structurally-related sulfonamides incorporating 1,3,5-triazinyl functionalities.     

Synthesis of 4-(thiazol-2-ylamino)-benzenesulfonamides with carbonic anhydrase I,II and IX inhibitory activity and cytotoxic effects against breast cancer cell lines

A series of 4-(thiazol-2-ylamino)-benzenesulfonamides was synthesized and screened for their carbonic anhydrase (CA, EC 4.2.1.1) inhibitory and cytotoxic activity on human breast cancer cell line MCF-7. Human (h) CA isoforms I, II and IX were included in the study. The new sulfonamides showed excellent inhibition of all three isoforms, with K_Is in the range of 0.84–702 nM against hCA I, of 0.41–288 nM against hCA II and of 5.6–29.2 against the tumor-associated hCA IX, a validated anti-tumor target, with a sulfonamide (SLC-0111) in Phase I clinical trials for the treatment of hypoxic, metastatic solid tumors overexpressing CA IX. The new compounds showed micromolar inhibition of growth efficacy against breast cancer MCF-7 cell lines.     

Fluorescent sulfonamide carbonic anhydrase inhibitors incorporating 1,2,3-triazole moieties: Kinetic and X-ray crystallographic studies

Fluorescent sulfonamide carbonic anhydrase (CA, EC 4.2.1.1) inhibitors (CAIs) were essential for demonstrating the role played by the tumor-associated isoform CA IX in acidification of tumors, cancer progression towards metastasis and for the development of imaging and therapeutic strategies for the management of hypoxic tumors which overexpress CA IX. However, the presently available such compounds are poorly water soluble which limits their use. Here we report new fluorescent sulfonamides 7, 8 and 10 with increased water solubility. The new derivatives showed poor hCA I inhibitory properties, but were effective inhibitors against the hCA II (K_Is of 366–127 nM), CA IX (K_Is of 8.1–36.9 nM), CA XII (K_Is of 4.1–20.5 nM) and CA XIV (K_Is of 12.8–53.6 nM). A high resolution X-ray crystal structure of one of these compounds bound to hCA II revealed the factors associated with the good inhibitory properties. Furthermore, this compound showed a three-fold increase of water solubility compared to a similar derivative devoid of the triazole moiety, making it an interesting candidate for ex vivo/in vivo studies.     

Structural study of the location of the phenyl tail of benzene sulfonamides and the effect on human carbonic anhydrase inhibition

The crystal structure of 4-phenylacetamidomethyl-benzenesulfonamide (4ITP) bound to human carbonic anhydrase (hCA, EC 4.2.1.1) II is reported. 4ITP is a medium potency hCA I and II inhibitor (K_Is of 54–75 nM), a strong mitochondrial CA VA/VB inhibitor (K_Is of 8.3–8.6 nM) and a weak transmembrane CA inhibitor (K_Is of 136–212 nM against hCA IX and XII). This elongated compound binds in an extended conformation to hCA II, with its tail lying towards the hydrophobic half of the active site whereas the sulfonamide moiety coordinates the zinc ion. The present structure was compared to that of structurally related aromatic sulfonamides, such as 4-phenylacetamido-benzene-sulfonamide (3OYS), 4-(2-mercaptophenylacetamido)-benzene-sulfonamide (2HD6) and 4-(3-nitrophenyl)-ureido-benzenesulfonamide (3N2P). Homology models of the hCA I, VA, VB, IX and XII structures were build which afforded an understanding of the amino acids involved in the binding of these compounds to these isoforms. The main conclusion of the study is that the orientation of the tail moiety and the presence of flexible linkers as well polar groups in it, strongly influence the potency and the selectivity of the sulfonamides for the inhibition of cytosolic, mitochondrial or transmembrane CA isoforms.     

Synthesis 4-[2-(2-mercapto-4-oxo-4H-quinazolin-3-yl)-ethyl]-benzenesulfonamides with subnanomolar carbonic anhydrase II and XII inhibitory properties

Condensation of substituted anthranilic acids with 4-isothiocyanatoethyl-benzenesulfonamide led to series of heterocyclic benzenesulfonamides incorporating 2-mercapto-quinazolin-4-one tails. These sulfonamides were investigated as inhibitors of the human carbonic anhydrase (hCA, EC 4.2.1.1) isoforms hCA I and II (cytosolic isozymes), as well as hCA XII (a transmembrane, tumor-associated enzyme also involved in glaucoma-genesis). The new sulfonamides acted as medium potency inhibitors of hCA I (K_Is of 28.5–2954 nM), being highly effective as hCA II (K_Is in the range of 0.62–12.4 nM) and XII (K_Is of 0.54–7.11 nM) inhibitors. All substitution patterns present in these compounds (e.g., halogens, methyl and methoxy moieties, in positions 6, 7 and/or 8 of the 2-mercapto-quinazolin-4-one ring) led to highly effective hCA II/XII inhibitors. These compounds should thus be of interest as preclinical candidates in pathologies in which the activity of these enzymes should be inhibited, such as glaucoma (CA II and XII as targets) or some tumors in which the activity of isoforms CA II and XII is dysregulated.     

Coumarinyl-substituted sulfonamides strongly inhibit several human carbonic anhydrase isoforms: solution and crystallographic investigations

We investigated a series of coumarinyl-substituted aromatic sulfonamides as inhibitors of four carbonic anhydrase (CA, EC 4.2.1.1) isoforms with medical applications, the cytosolic hCA I, and II, and the transmembrane, tumor-associated hCA IX and XII. Compounds incorporating 7-methoxy-coumarin-4-yl-acetamide-tails and benzenesulfonamide and benzene-1,3-disulfonamide scaffolds showed medium potency inhibition of hCA I (K_Is of 73–131 nM), effective hCA II inhibition (K_Is of 9.1–36 nM) and less effective hCA IX and XII inhibition (K_Is of 55–128 nM). Only one compound, the derivatized 4-amino-6-trifluoromethyl-benzene-1,3-disulfonamide with the coumarinyl tail, showed effective inhibition of the transmembrane isoforms, with K_Is of 5.9–14.2 nM, although it was less effective as hCA I and II inhibitor (K_Is of 36–120 nM). An X-ray crystal structure of hCA II in complex with 4-(7-methoxy-coumarin-4-yl-acetamido)-benzenesulfonamide (K_I of 9.1 nM against hCA II) showed the intact inhibitor coordinated to the zinc ion from the enzyme active site by the sulfonamide moiety, and participating in a edge-to-face stacking with Phe131, in addition to other hydrophobic and hydrophilic interactions with water molecules and amino acid residues from the active site. Thus, sulfonamides incorporating coumarin rings have a distinct inhibition mechanism compared to the coumarins, and may lead to compounds with interesting inhibition profiles against various α-CAs found in mammals or parasites, such as Plasmodium falciparum.     

Synthesis and biological evaluation of novel tris-chalcones as potent carbonic anhydrase,acetylcholinesterase, butyrylcholinesterase and α-glycosidase inhibitors

A novel class of fluoro-substituted tris-chalcones derivatives (5a-5i) was synthesized from phloroglucinol and corresponding benzaldehydes. A three step synthesis method was followed for the production of these tris-chalcone compounds. The structures of the newly synthesized compounds (5a-5i) were confirmed on the basis of IR, ¹H NMR, ¹³C NMR, and elemental analysis. The compounds’ inhibitory activities were tested against human carbonic anhydrase I and II isoenzymes (hCA I and hCA II), acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and α-glycosidase (α-Gly). These chalcone derivatives had K_i values in the range of 19.58–78.73 nM for hCA I, 12.23–41.70 nM for hCA II, 1.09–6.84 nM for AChE, 8.30–32.30 nM for BChE and 0.93 ± 0.20–18.53 ± 5.06 nM against α-glycosidase. These results strongly support the promising nature of the tris-chalcone scaffold as selective carbonic anhydrase, acetylcholinesterase, butyrylcholinesterase, and α-glycosidase inhibitor. Overall, due to these derivatives’ inhibitory potential on the tested enzymes, they are promising drug candidates for the treatment of diseases like glaucoma, leukemia, epilepsy; Alzheimer’s disease; type-2 diabetes mellitus that are associated with high enzymatic activity of carbonic anhydrase, acetylcholine esterase, butyrylcholinesterase, and α-glycosidase.     

Development of 3-(4-aminosulphonyl)-phenyl-2-mercapto-3H-quinazolin-4-ones as inhibitors of carbonic anhydrase isoforms involved in tumorigenesis and glaucoma

A series of heterocyclic benzenesulfonamides incorporating 2-mercapto-3H-quinazolin-4-one tails were prepared by condensation of substituted anthranilic acids with 4-isothiocyanato-benzenesulfonamide. These sulfonamides were investigated as inhibitors of the human carbonic anhydrase (hCA, EC 4.2.1.1) isoforms hCA I and II (cytosolic isozymes), as well as hCA IX and XII (trans-membrane, tumor-associated enzymes). They acted as medium potency inhibitors of hCA I (K_Is of 81.0–3084 nM), being highly effective as hCA II (K_Is in the range of 0.25–10.8 nM), IX (K_Is of 3.7–50.4 nM) and XII (K_Is of 0.60–52.9 nM) inhibitors. These compounds should thus be of interest as preclinical candidates in pathologies in which the activity of these enzymes should be inhibited, such as glaucoma (CA II and XII as targets) or some tumors in which the activity of three isoforms (CA II, IX and XII) is dysregulated.     

Facile synthesis and characterization of novel pyrazole-sulfonamides and their inhibition effects on human carbonic anhydrase isoenzymes

In the current study, a series of pyrazole-sulfonamide derivatives (2–14) were synthesized, characterized, and the inhibition effects of the derivatives on human carbonic anhydrases (hCA I and hCA II) were investigated as in vitro. Structures of these sulfonamides were confirmed by FT-IR, ¹H NMR, ¹³C NMR and LC–MS analysis. ¹H NMR and ¹³C NMR revealed the tautomeric structures. hCA I and hCA II isozymes were purified from human erythrocytes and inhibitory effects of newly synthesized sulfonamides on esterase activities of these isoenzymes have been studied. The K_i values of compounds were 0.062–1.278 μM for hCA I and 0.012–0.379 μM for hCA II. The inhibition effects of 7 for hCA I and 4 for hCA II isozymes were almost in nanomolar concentration range.     

Acetylcholinesterase and carbonic anhydrase inhibitory properties of novel urea and sulfamide derivatives incorporating dopaminergic 2-aminotetralin scaffolds

In the present study a series of urea and sulfamide compounds incorporating the tetralin scaffolds were synthesized and evaluated for their acetylcholinesterase (AChE), human carbonic anhydrase (CA, EC 4.2.1.1) isoenzyme I, and II (hCA I and hCA II) inhibitory properties. The urea and their sulfamide analogs were synthesized from the reactions of 2-aminotetralins with N,N-dimethylcarbamoyl chloride and N,N-dimethylsulfamoyl chloride, followed by conversion to the corresponding phenols via O-demethylation with BBr₃. The novel urea and sulfamide derivatives were tested for inhibition of hCA I, II and AChE enzymes. These derivatives exhibited excellent inhibitory effects, in the low nanomolar range, with K_i values of 2.61–3.69 nM against hCA I, 1.64–2.80 nM against hCA II, and in the range of 0.45–1.74 nM against AChE. In silico techniques such as, atomistic molecular dynamics (MD) and molecular docking simulations, were used to understand the scenario of the inhibition mechanism upon approaching of the ligands into the active site of the target enzymes. In light of the experimental and computational results, crucial amino acids playing a role in the stabilization of the enzyme–inhibitor adducts were identified.     

Benzenesulfonamide bearing 1,2,4-triazole scaffolds as potent inhibitors of tumor associated carbonic anhydrase isoforms hCA IX and hCA XII

Three series of novel heterocyclic compounds (3a–3g, 4a–4g and 5a–5g) containing benzenesulfonamide moiety and incorporating a 1,2,4-triazole ring, have been synthesized and investigated as inhibitors against four isomers of the α-class carbonic anhydrases (CAs, EC 4.2.1.1), comprising hCAs I and II (cytosolic, ubiquitous isozymes) and hCAs IX and XII (transmembrane, tumor associated isozymes). Against the human isozymes hCA I and II, compounds of two series (3a–3g and 4a–4g) showed K_i values in the range of 84–868 nM and 5.6–390 nM, respectively whereas compounds of series 5a–5g were found to be poor inhibitors (K_i values exceeding 10,000 nM in some cases). Against hCA IX and XII, all the tested compounds exhibited excellent to moderate inhibitory potential with K_i values in the range of 2.8–431 nM and 1.3–63 nM, respectively. Compounds 3d, 3f and 4f exhibited excellent inhibitory potential against all of the four isozymes hCA I, II, IX and XII, even better than the standard drug acetazolamide (AZA) whereas compound of the series 5a–5g were comparatively less potent but more selective towards hCA IX and XII.     

Microwave assisted synthesis of novel acridine–acetazolamide conjugates and investigation of their inhibition effects on human carbonic anhydrase isoforms hCA I,II, IV and VII

4-Amino-N-(5-sulfamoyl-1,3,4-thiadiazol-2-yl)benzamide was condensed with cyclic-1,3-diketones (dimedone and cyclohexane-1,3-dione) and aromatic aldehydes under microwave irradiation, leading to a series of acridine–acetazolamide conjugates. The new compounds were investigated as inhibitors of carbonic anhydrases (CA, EC 4.2.1.1), and more precisely cytosolic isoforms hCA I, II, VII and membrane-bound one hCA IV. All investigated isoforms were inhibited in low micromolar and nanomolar range by the new compounds. hCA IV and VII were inhibited with K_Is in the range of 29.7–708.8 nM (hCA IV), and of 1.3–90.7 nM (hCA VII). For hCA I and II the K_Is were in the range of 6.7–335.2 nM (hCA I) and of 0.5–55.4 nM (hCA II). The structure–activity relationships (SAR) for the inhibition of these isoforms with the acridine–acetazolamide conjugates reported here were delineated.     

Carbonic anhydrase inhibitors. Aromatic/heterocyclic sulfonamides incorporating phenacetyl,pyridylacetyl and thienylacetyl tails act as potent inhibitors of human mitochondrial isoforms VA and VB

A series of aromatic/heterocyclic sulfonamides incorporating phenyl(alkyl), halogenosubstituted-phenyl- or 1,3,4-thiadiazole-sulfonamide moieties and thienylacetamido; phenacetamido and pyridinylacetamido tails were prepared and assayed as inhibitors of four physiologically relevant carbonic anhydrase (CA, EC 4.2.1.1) isoforms, the cytosolic human (h) hCA I and hCA II, and the mitochondrial hCA VA and hCA VB. The new compounds showed moderate inhibition of the two cytosolic isoforms (K_Is of 50–390 nM) and excellent inhibitory activity against the two mitochondrial enzymes, with many low nanomolar inhibitors detected (K_Is in the range of 5.9–10.2 nM). All substitution patterns explored here lead to effective hCA VA/VB inhibitors. Some hCA VA/VB selective inhibitors were also detected, with selectivity ratios for inhibiting the mitochondrial over the cytosolic isozymes of around 55.5–56.9. As hCA VA/VB are involved in several biosynthetic processes catalyzed by pyruvate carboxylase, acetyl CoA carboxylase, and carbamoyl phosphate synthetases I and II, providing the bicarbonate substrate to these carboxylating enzymes involved in fatty acid biosynthesis, their selective inhibition may lead to the development of antiobesity agents possessing a new mechanism of action.     

7-Substituted-sulfocoumarins are isoform-selective,potent carbonic anhydrase II inhibitors

A series of 7-substituted sulfocoumarins and 3,4-dihydrosulfocoumarins was obtained by cyclization of the methanesulfonate of 2,4-dihydroxy- or 2-hydroxy-4-methoxybenzaldehyde, followed by derivatization reactions. The new compounds incorporate a range of substituents in position 7 of the heterocyclic ring (hydroxyl, methoxy, carboxylic and alkylsulfonate ester). The compounds were tested for the inhibition of the zinc enzyme human (h) carbonic anhydrase (hCA, EC 4.2.1.1). Unlike the 6-substituted sulfocoumarins which were potent hCA IX and XII inhibitors and ineffective hCA I and II inhibitors, compounds from this series showed low nanomolar hCA II inhibitory properties, and inhibited the mitochondrial isoform hCA VA with K_Is in the range of 91–9960 nM, but were ineffective as hCA I, IX and XII inhibitors. The structure activity relationship for this class of inhibitors was rather clear, with the nature of the 7-substituent strongly influencing hCA VA inhibition, whereas the nature of these groups were less relevant for hCA II inhibition (all reported compounds were highly effective hCA II inhibitors, with K_Is in the range of 1.5–8.4 nM). Since both hCA II and hCA VA are important drug targets (hCA II for antiglaucoma agents; hCA VA for antiobesity drugs), these isoform-selective inhibitors reported here may be considered of interest for various biomedical applications.     

Carbonic anhydrase inhibitory properties of novel benzylsulfamides using molecular modeling and experimental studies

In this study, a series of sulfamoyl carbamates and sulfamide derivatives were synthesized. Six commercially available benzyl amines and BnOH were reacted with chlorosulfonyl isocyanate (CSI) to give sulfamoyl carbamates. Pd–C catalyzed hydrogenolysis reactions of carbamates afforded sulfamides. The inhibition effects of novel benzylsulfamides on the carbonic anhydrase I, and II isoenzymes (CA I, and CA II) purified from fresh human blood red cells were determined by Sepharose-4B-L-Tyrosine-sulfanilamide affinity chromatography. In vitro studies were shown that all of novel synthesized benzylsulfamide analogs inhibited, concentration dependently, both hCA isoenzyme activities. The novel benzylsulfamide compounds investigated here exhibited nanomolar inhibition constants against the two isoenzymes. K_i values were in the range of 28.48 ± 0.01–837.09 ± 0.19 nM and 112.01 ± 0.01–268.01 ± 0.22 nM for hCAI and hCA II isoenzymes, respectively. Molecular modeling approaches were also applied for studied compounds.     

Carbonic anhydrase inhibitors. Inhibition of human cytosolic isoforms I and II with (reduced) Schiff’s bases incorporating sulfonamide,carboxylate and carboxymethyl moieties

A library of Schiff bases was synthesized by condensation of aromatic amines incorporating sulfonamide, carboxylic acid or carboxymethyl functionalities as Zn²⁺-binding groups, with aromatic aldehydes incorporating tert-butyl, hydroxy and/or methoxy groups. The corresponding amines were thereafter obtained by reduction of the imines. These compounds were assayed for the inhibition of two cytosolic human carbonic anhydrase (hCA, EC 4.2.1.1) isoenzymes, hCA I and II. The K_i values of the Schiff bases were in the range of 7.0–21,400 nM against hCA II and of 52–8600 nM against hCA I, respectively. The corresponding amines showed K_i values in the range of 8.6 nM–5.3 μM against hCA II, and of 18.7–251 nM against hCA I, respectively. Unlike the imines, the reduced Schiff bases are stable to hydrolysis and several low-nanomolar inhibitors were detected, most of them incorporating sulfonamide groups. Some carboxylates also showed interesting CA inhibitory properties. Such hydrosoluble derivatives may show pharmacologic applications.