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

1,3-Diaryl Triazenes Incorporating Disulfonamides Show Both Antiproliferative Activity and Effective Inhibition of Tumor-associated Carbonic Anhydrases IX and XII

AIM

The aim of this study was to synthesize a library of novel di-sulfa drugs containing 1,3- diaryltriazene derivatives TS (1-13) by conjugation of diazonium salts of primary sulfonamides with sulfa drugs to investigate the cytotoxic effect of these new compounds in different cancer types and to determine their inhibitory activity against tumor-associated carbonic anhydrases IX and XII.

MATERIALS AND METHODS

A carbonic anhydrase inhibitory activity of the obtained compounds was evaluated against four selected human carbonic anhydrase isoforms (hCA I, hCA II, hCA IX and hCA XII) by a stoppedflow CO2 hydrase assay. In addition, in vitro, cytotoxicity studies were applied by using A549 (lung cancer), BEAS-2B (normal lung), MCF-7 (breast cancer), MDA-MB-231 (breast cancer), CRL-4010 (normal breast epithelium), HT-29 (colon cancer), and HCT -116 (colon cancer) cell lines.

RESULTS

As a result of the inhibition data, the 4-aminobenzenesulfonamide derivatives were more active than their 3-aminobenzenesulfonamide counterparts. More specifically, compounds TS-1 and TS-2, both of which have primary sulfonamides on both sides of the triazene linker, showed the best inhibitory activity against hCA IX with Ki values of 19.5 and 13.7 nM and also against hCA XII with Ki values of 6.6 and 8.3 nM, respectively. In addition, in vitro cytotoxic activity on the human breast cancer cell line MCF-7 showed that some derivatives of di-sulfa triazenes, such as TS-5 and TS-13, were more active than SLC-0111.

CONCLUSION

With the aim of developing more potent and isoform-selective CA inhibitors, these novel hybrid molecules containing sulfa drugs, triazene linkers, and the classical primary sulfonamide chemotype may be considered an interesting example of effective enzyme inhibitors and important anticancer agents.

Potent carbonic anhydrase I, II, IX and XII inhibition activity of novel primary benzenesulfonamides incorporating bis-ureido moieties

A novel series of twelve aromatic bis-ureido-substituted benzenesulfonamides was synthesised by conjugation of aromatic aminobenzenesulfonamides with aromatic bis-isocyanates. The obtained bis-ureido-substituted derivatives were tested against four selected human carbonic anhydrase isoforms (hCA I, hCA II, hCA IX and hCA XII). Most of the new compounds showed an effective inhibitory profile against isoforms hCA IX and hCA XII, also having some selectivity with respect to hCA I and hCA II. The inhibition constants of these compounds against isoforms hCA IX and XII were in the range of 6.73-835 and 5.02-429 nM, respectively. Since hCA IX and hCA XII are important drug targets for anti-cancer/anti-metastatic drugs, these effective inhibitors reported here may be considered of interest for cancer related studies in which these enzymes are involved.

Evaluation of cytotoxic, antifungal, and larvicidal activities of different bis-sulfonamide Schiff base compounds

Schiff bases (imines or azomethines) are versatile ligands synthesized from the condensation of amino compounds with active carbonyl groups and used for many pharmaceutical and medicinal applications. In our study, we aimed to determine the cytotoxic, antifungal and larvicidal activities of biologically potent bis-sulfonamide Schiff base derivatives that were re-synthesized by us. For this aim, 16 compounds were re-synthesized and tested for their cytotoxic, antifungal and larvicidal properties. Among this series, compounds A1B2, A1B4, A4B2, A4B3, and A4B4 were shown to have cytotoxic activity against tested cancer lung cell line (A549). The most potent antifungal activity was observed in compounds A2B1 and A2B2 against all fungi. A1B1 showed the strongest larvicidal effect at all concentrations at the 72nd h (100% mortality). These obtained results demonstrate that these type of bis-substituted compounds might be used as biologically potent pharmacophores against different types of diseases.

New Ni(II) and Pd(II) complexes bearing derived sulfa drug ligands: synthesis, characterization, DFT calculations, and in silico and in vitro biological activity studies

In the present study, the synthesis of six new Ni(II) and Pd(II) complexes with three derived sulfamethoxazole drug ligands is reported. The coordination mode, geometry, and chemical formula of all the synthesized compounds have been determined by elemental analysis, mass spectrometry, emission atomic spectroscopy, conductivity measurements, magnetic susceptibility, FTIR, TGA, 1H-NMR, electronic absorption spectroscopy, SEM-EDX along with DFT calculations. The Schiff Base ligands were found to be bidentate and coordinated to the metal ions through sulfonamidic nitrogen and oxazolic nitrogen atoms leading to a square planar geometry for palladium (II) while a distorted octahedral geometry around Nickel (II) ion was suggested. Biological applications of the new complexes including in vitro antimicrobial, antioxidant and anticancer properties were investigated. The results showed that the new metal (II) compounds exhibit remarkable antibacterial inhibition activity against both Gram-positive and Gram-negative bacteria, in addition to noticeable DPPH free radical scavenging activity. The in vitro cytotoxicity assay of the complexes against cell lines of chronic myelogenous leukaemia (K562) showed promising potential for the application of the coordination compounds in antitumor therapy. Subsequently, to evaluate the pharmaceutical potential of the metal-containing compounds, pharmacokinetics and toxicity were studied by ADMET simulations while interactions between the complexes and bacterial proteins were evaluated by molecular docking.

Activation studies with amino acids and amines of a β-carbonic anhydrase from Mammaliicoccus (Staphylococcus) sciuri previously annotated as Staphylococcus aureus (SauBCA) carbonic anhydrase

A β-carbonic anhydrase (CA, EC 4.2.1.1) previously annotated to be present in the genome of Staphylococcus aureus, SauBCA, has been shown to belong to another pathogenic bacterium, Mammaliicoccus (Staphylococcus) sciuri. This enzyme, MscCA, has been investigated for its activation with a series of natural and synthetic amino acid and amines, comparing the results with those obtained for the ortholog enzyme from Escherichia coli, EcoCAβ. The best MscCA activators were D-His, L- and D-DOPA, 4-(2-aminoethyl)-morpholine and L-Asn, which showed K_As of 0.12 - 0.89 µM. The least efficient activators were D-Tyr and L-Gln (K_As of 13.9 - 28.6 µM). The enzyme was also also inhibited by anions and sulphonamides, as described earlier. Endogenous CA activators may play a role in bacterial virulence and colonisation of the host which makes this research topic of great interest.

Carbonic Anhydrase Activators for Neurodegeneration: An Overview

Carbonic anhydrases (CAs) are a family of ubiquitous metal enzymes catalyzing the reversible conversion of CO₂ and H₂O to HCO₃⁻ with the release of a proton. They play an important role in pH regulation and in the balance of body fluids and are involved in several functions such as homeostasis regulation and cellular respiration. For these reasons, they have been studied as targets for the development of agents for treating several pathologies. CA inhibitors have been used in therapy for a long time, especially as diuretics and for the treatment of glaucoma, and are being investigated for application in other pathologies including obesity, cancer, and epilepsy. On the contrary, CAs activators are still poorly studied. They are proposed to act as additional (other than histidine) proton shuttles in the rate-limiting step of the CA catalytic cycle, which is the generation of the active hydroxylated enzyme. Recent studies highlight the involvement of CAs activation in brain processes essential for the transmission of neuronal signals, suggesting CAs activation might represent a potential therapeutic approach for the treatment of Alzheimer’s disease and other conditions characterized by memory impairment and cognitive problems. Actually, some compounds able to activate CAs have been identified and proposed to potentially resolve problems related to neurodegeneration. This review reports on the primary literature regarding the potential of CA activators for treating neurodegeneration-related diseases.

New Histamine-Related Five-Membered N-Heterocycle Derivatives as Carbonic Anhydrase I Activators

A series of histamine (HST)-related compounds were synthesized and tested for their activating properties on five physiologically relevant human Carbonic Anhydrase (hCA) isoforms (I, II, Va, VII and XIII). The imidazole ring of HST was replaced with different 5-membered heterocycles and the length of the aliphatic chain was varied. For the most interesting compounds some modifications on the terminal amino group were also performed. The most sensitive isoform to activation was hCA I (K_A values in the low micromolar range), but surprisingly none of the new compounds displayed activity on hCA II. Some derivatives (1, 3a and 22) displayed an interesting selectivity for activating hCA I over hCA II, Va, VII and XIII.

Amine- and Amino Acid-Based Compounds as Carbonic Anhydrase Activators

After being rather neglected as a research field in the past, carbonic anhydrase activators (CAAs) were undoubtedly demonstrated to be useful in diverse pharmaceutical and industrial applications. They also improved the knowledge of the requirements to selectively interact with a CA isoform over the others and confirmed the catalytic mechanism of this class of compounds. Amino acid and amine derivatives were the most explored in in vitro, in vivo and crystallographic studies as CAAs. Most of them were able to activate human or non-human CA isoforms in the nanomolar range, being proposed as therapeutic and industrial tools. Some isoforms are better activated by amino acids than amines derivatives and the stereochemistry may exert a role. Finally, non-human CAs have been very recently tested for activation studies, paving the way to innovative industrial and environmental applications.

Biological effects of bis-hydrazone compounds bearing isovanillin moiety on the aldose reductase

Aldose reductase (ALR2), one of the metabolically important enzymes, catalyzes the formation of sorbitol from glucose in the polyol pathway. ALR2 inhibition is required to prevent diabetic complications. In the present study, the novel bis-hydrazone compounds bearing isovanillin moiety (GY1-12) were synthesized, and various chromatographic methods were applied to purify the ALR2 enzyme. Afterward, the inhibitory effect of the synthesized compounds on the ALR2 was screened in vitro. All the novel bis-hydrazones demonstrated activity in nanomolar levels as AR inhibitors with IC₅₀ and K_I values in the range of 12.55-35.04 nM, and 13.38-88.21 nM, respectively. Compounds GY-11, GY-7, and GY-5 against ALR2 were identified as the highly potent inhibitors, respectively, and were superior to the standard drug, epalrestat. Moreover, a comprehensive ligand-receptor interactions prediction was performed using ADME-Tox, Glide XP, and MM-GBSA modules of Schrödinger Small-Molecule Drug Discovery Suite to elucidate the novel bis-hydrazone derivatives, potential binding modes versus the ALR2. As a result, these compounds with ALR2 inhibitory effects may be potential alternative agents that can be used to treat or prevent diabetic complications.

Quantum mechanical study on the activation mechanism of human carbonic anhydrase VII cluster model with bis-histamine schiff bases and bis-spinaceamine derivatives

The activation mechanism of human carbonic anhydrase (hCA) isoform VII, hCA VII, with histamine, histamine bis-Schiff bases and bis-spinaceamine derivatives has been investigated using quantum mechanical calculations. The DFT-D3 method has been employed to calculate in detail the electronic structure and electronic energy of different compounds and complexes throughout the reaction pathway. The model system of hCA VII included the core catalytic center, the Zn²⁺ ion, its three histidine ligands and a hydroxide ion or water molecule coordinated to it. Furthermore, Thr199, Glu106 and the deep water molecule were considered in the model. Five activators of this enzyme, including histamine as standard, in complex with the cluster model of hCA VII were investigated. Thermodynamic functions for the overall reaction and for the complexation between activators and hCA VII were evaluated. Our results demonstrate that the protonatable moiety of these activators participates in proton transfer reactions from the zinc-bound water molecule to the reaction medium, promoting the formation of the catalytically active zinc hydroxide species of the enzyme. The QM analysis revealed that the electrostatic interactions between activators and hCA VII are the driving force of the enzyme-activator complex formation.

3-Functionalised benzenesulphonamide based 1,3,4-oxadiazoles as selective carbonic anhydrase XIII inhibitors: Design, synthesis and biological evaluation

A new series of benzenesulphonamide linked-1,3,4-oxadiazole hybrids (6a-s) has been synthesized and tested for their carbonic anhydrase inhibition against human (h) carbonic anhydrase (CA) isoforms hCA I, II, IX, and XIII. Fluorescence properties of some of the synthesized molecules were studied. Most of the molecules exhibited significant inhibitory power, comparable or better than the standard drug acetazolamide (AAZ) on hCA XIII. Out of 19 tested molecules, compound 6e (75.8 nM) was 3 times more potent than AAZ (250.0 nM) against hCA I, whereas compound 6e (15.4 nM), 6g (16.2 nM), 6h (16.4 nM) and 6i (17.0 nM) were found to be more potent than AAZ (17.0 nM) against isoform hCA XIII. It is anticipated that these compounds could be taken as the potential leads for the development of selective hCA XIII isoform inhibitors with improved potency.

Synthesis and carbonic anhydrase activating properties of a series of 2-amino-imidazolines structurally related to clonidine1

The Carbonic Anhydrase (CA, EC 4.2.1.1) activating properties of histamine have been known for a long time. This compound has been extensively modified but only in few instances the imidazole ring has been replaced with other heterocycles. It was envisaged that the imidazoline ring could be a bioisoster of the imidazole moiety. Indeed, we report that clonidine, a 2-aminoimidazoline derivative, was found able to activate several human CA isoforms (hCA I, IV, VA, VII, IX, XII and XIII), with potency in the micromolar range, while it was inactive on hCA II. A series of 2-aminoimidazoline, structurally related to clonidine, was then synthesised and tested on selected hCA isoforms. The compounds were inactive on hCA II while displayed activating properties on hCA I, VA, VII and XIII, with K_A values in the micromolar range. Two compounds (10 and 11) showed some preference for the hCA VA or VII isoforms.

Activation studies of the β-carbonic anhydrases from Malassezia restricta with amines and amino acids

The β-carbonic anhydrase (CA, EC 4.2.1.1) from the genome of the opportunistic pathogen Malassezia restricta (MreCA), which was recently cloned and characterised, herein has been investigated for enzymatic activation by a panel of amines and amino acids. Of the 24 compounds tested in this study, the most effective MreCA activators were L-adrenaline (KA of 15 nM), 2-aminoethyl-piperazine/morpholine (KAs of 0.25-0.33 µM), histamine, L-4-amino-phenylalanine, D-Phe, L-/D-DOPA, and L-/D-Trp (KAs of 0.32 - 0.90 µM). The least effective activators were L-/D-Tyr, L-Asp, L-/D-Glu, and L-His, with activation constants ranging between 4.04 and 12.8 µM. As MreCA is involved in dandruff and seborrhoeic dermatitis, these results are of interest to identify modulators of the activity of enzymes involved in the metabolic processes of such fungi.

A structure-based approach towards the identification of novel antichagasic compounds: Trypanosoma cruzi carbonic anhydrase inhibitors

Trypanosoma cruzi carbonic anhydrase (TcCA) has recently emerged as an interesting target for the design of new compounds to treat Chagas disease. In this study we report the results of a structure-based virtual screening campaign to identify novel and selective TcCA inhibitors. The combination of properly validated computational methodologies such as comparative modelling, molecular dynamics and docking simulations allowed us to find high potency hits, with KI values in the nanomolar range. The compounds also showed trypanocidal effects against T. cruzi epimastigotes and trypomastigotes. All the candidates are selective for inhibiting TcCA over the human isoform CA II, which is encouraging in terms of possible therapeutic safety and efficacy.

Activation studies of the β-carbonic anhydrases from Escherichia coli with amino acids and amines

A β-carbonic anhydrase (CA, EC 4.2.1.1) from the widespread bacterium Escherichia coli (EcoCAβ), encoded by the CynT2 gene, has been investigated for its catalytic properties and enzymatic activation by a panel of amino acids and amines. EcoCAβ showed a significant catalytic activity for the hydration of CO2 to bicarbonate and a proton, with a kinetic constant kcat of 5.3 × 105 s- and a Michaelis-Menten constant KM of 12.9 mM. The most effective EcoCAβ activators were L- and D-DOPA, L-Tyr, 4-amino-Phe, serotonin and L-adrenaline, with KAs from 2.76 to 10.7 µM. L-His, 2-pyridyl-methylamine, L-Asn and L-Gln were relatively weak activators (KAs from 36.0 to 49.5 µM). D-His, L- and D-Phe, L- and D-Trp, D-Tyr, histamine, dopamine, 2-(aminoethyl)pyridine/piperazine/morpholine, L-Asp, L- and D-Glu have KAs from 11.3 to 23.7 µM. Endogenous CA activators may play a role in bacterial virulence and colonisation of the host.

Synthesis of calix[4]azacrown substituted sulphonamides with antioxidant, acetylcholinesterase, butyrylcholinesterase, tyrosinase and carbonic anhydrase inhibitory action

A series of novel calix[4]azacrown substituted sulphonamide Schiff bases was synthesised by the reaction of calix[4]azacrown aldehydes with different substituted primary and secondary sulphonamides. The obtained novel compounds were investigated as inhibitors of six human (h) isoforms of carbonic anhydrases (CA, EC 4.2.1.1). Their antioxidant profile was assayed by various bioanalytical methods. The calix[4]azacrown substituted sulphonamide Schiff bases were also investigated as inhibitors of acetylcholinesterase (AChE), butyrylcholinesterase (BChE) and tyrosinase enzymes, associated with several diseases such as Alzheimer, Parkinson, and pigmentation disorders. The new sulphonamides showed low to moderate inhibition against hCAs, AChE, BChE, and tyrosinase enzymes. However, some of them possessed relevant antioxidant activity, comparable with standard antioxidants used in the study.

(Hetero)aryl substituted thiazol-2,4-yl scaffold as human carbonic anhydrase I, II, VII and XIV activators

Using histamine as lead molecule, a library of (hetero)aryl substituted thiazol-2,4-yl derivatives incorporating pyridine as proton shuttling moiety were obtained and investigated as activators of human carbonic anhydrase (CA, EC 4.2.1.1) isoforms I, II, VII and XIV. Some derivatives displayed good activating and selectivity profiles. This study provides an interesting opportunity to study the thiazole scaffold for the design of CA activators (CAAs), possibly acting on the central nervous system and targeting pathologies involving memory and learning impairments.

Synthesis and biological evaluation of novel 3-(quinolin-4-ylamino)benzenesulfonamidesAQ3 as carbonic anhydrase isoforms I and II inhibitors

Carbonic anhydrases (CAs, EC 4.2.1.1) are crucial metalloenzymes that are involved in diverse bioprocesses. We report the synthesis and biological evaluation of novel series of benzenesulfonamides incorporating un/substituted ethyl quinoline-3-carboxylate moieties. The newly synthesised compounds were in vitro evaluated as inhibitors of the cytosolic human (h) isoforms hCA I and II. Both isoforms hCA I and II were inhibited by the quinolines reported here in variable degrees: hCA I was inhibited with KIs in the range of 0.966-9.091 μM, whereas hCA II in the range of 0.083-3.594 μM. The primary 7-chloro-6-flouro substituted sulphfonamide derivative 6e (KI = 0.083 μM) proved to be the most active quinoline in inhibiting hCA II, whereas, its secondary sulfonamide analog failed to inhibit the hCA II up to 10 μM, confirming the crucial role of the primary sulphfonamide group, as a zinc-binding group for CA inhibitory activity.

Activation of α-, β-, γ- δ-, ζ- and η- class of carbonic anhydrases with amines and amino acids: a review

Eight genetically distinct carbonic anhydrase (EC 4.2.1.1) enzyme families (α-, β-, γ- δ-, ζ-, η-, θ- and ι-CAs) were described to date. On the other hand, 16 mammalian α-CA isoforms are known to be involved in many diseases such as glaucoma, edema, epilepsy, obesity, hypoxic tumors, neuropathic pain, arthritis, neurodegeneration, etc. Although CA inhibitors were investigated for the management of a variety of such disorders, the activators just started to be investigated in detail for their in vivo effects. This review summarizes the activation profiles of α-, β, γ-, δ-, ζ- and η- CAs from various organisms (animals, fungi, protozoan, bacteria and archaea) with the most investigated classes of activators, the amines and the amino acids.

The first activation study of the β-carbonic anhydrases from the pathogenic bacteria Brucella suis and Francisella tularensis with amines and amino acids

The activation of the β-class carbonic anhydrases (CAs, EC 4.2.1.1) from the bacteria Brucella suis and Francisella tularensis with amine and amino acids was investigated. BsuCA 1 was sensitive to activation with amino acids and amines, whereas FtuCA was not. The most effective BsuCA 1 activators were L-adrenaline and D-Tyr (K_As of 0.70–0.95 µM). L-His, L-/D-Phe, L-/D-DOPA, L-Trp, L-Tyr, 4-amino-L-Phe, dopamine, 2-pyridyl-methylamine, D-Glu and L-Gln showed activation constants in the range of 0.70–3.21 µM. FtuCA was sensitive to activation with L-Glu (K_A of 9.13 µM). Most of the investigated compounds showed a weak activating effect against FtuCA (K_As of 30.5–78.3 µM). Many of the investigated amino acid and amines are present in high concentrations in many tissues in vertebrates, and their role in the pathogenicity of the two bacteria is poorly understood. Our study may bring insights in processes connected with invasion and pathogenic effects of intracellular bacteria.

Activation of human α-carbonic anhydrase isoforms I, II, IV and VII with bis-histamine schiff bases and bis-spinaceamine substituted derivatives

A series of histamine bis-Schiff bases and bis-spinaceamine derivatives were synthesised 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, with activation constants in the range of 4.73–10.2 µM for hCA I, 6.15–42.1 µM for hCA II, 2.37–32.7 µM for hCA IV and 32 nM–18.7 µM for hCA VII, respectively. The nature of the spacer between the two histamine/spinaceamine units of these molecules was the main contributor to the diverse activating efficacy, with a very different fine tuning for the diverse isoforms. As CA activators recently emerged as interesting agents for enhancing cognition, in the management of CA deficiencies, or for therapy memory and artificial tissues engineering, our compounds may be considered as candidates for such applications.

Synthesis and biological evaluation of novel 8-substituted quinoline-2-carboxamides as carbonic anhydrase inhibitors

A series of novel 8-substituted-N-(4-sulfamoylphenyl)quinoline-2-carboxamides was synthesised by the reaction of 8-hydroxy-N-(4-sulfamoylphenyl) quinoline-2-carboxamide with alkyl and benzyl halides. The compounds were assayed for carbonic anhydrase (CA) inhibitory activity against four hCA isoforms, hCA I, hCA II, hCA IV, and hCA IX. Barring hCA IX, all the isoforms were inhibited from low to high nanomolar range. hCA I was inhibited in the range of 61.9–8126 nM, with compound 5h having an inhibition constant of K_I = 61.9 nM. hCA II was inhibited in the range of 33.0–8759 nM, with compound 5h having an inhibition constant of 33.0 nM and compounds 5a and 5b having inhibition constants of 88.4 and 85.7 nM, respectively. hCA IV was inhibited in the range of 657.2–6757 nM. Hence, compound 5h, possessing low nanomolar hCA I and II inhibition, can be selected as a lead for the design of novel CA I and II inhibitors.

Discovery of new ureido benzenesulfonamides incorporating 1,3,5-triazine moieties as carbonic anhydrase I, II, IX and XII inhibitors

A series of twenty novel ureido benzenesulfonamides incorporating 1,3,5-triazine moieties substituted on one side with aromatic amines and on the other side with dimethylamine, morpholine and piperidine is reported. The compounds were synthesized from the 4-(3-(4,6-dichloro-1,3,5-triazin-2-yl)ureido)benzensulfonamide (1) by using stepwise nucleophilic substitution of the chlorine atoms of cyanuric chloride. The intermediates 2(a-e) and final compounds 3(a-o) were tested for their efficiency as carbonic anhydrase (CA) inhibitors against four selected physiologically relevant human carbonic anhydrase (CA, EC 4.2.1.1) isoforms, namely, the cytosolic ones hCA I and II, and the transmembrane, tumor associated ones hCA IX, and XII. The compounds 2a, 2e and 3m showed the highest activity for hCA IX with Kis in the range of 11.8-14.6 nM. Most of the compounds showed high hCA IX selectivity over the abundant off-target isoforms hCA I and II. Since hCA IX is a validated drug target for anticancer/antimetastatic agents, these isoform-selective and potent inhibitors may be considered of interest for further medicinal/pharmacologic studies.

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.

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 KAs 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 (KA of 16.2 µM for hCA II), 2-benzyl-piperazine (KA of 17.1 µM for hCA VII), and 1-(3-benzylpiperazin-1-yl)propan-1-one (KA 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.

Activation studies with amines and amino acids of the β-carbonic anhydrase encoded by the Rv3273 gene from the pathogenic bacterium Mycobacterium tuberculosis

The activation of a β-class carbonic anhydrase (CAs, EC 4.2.1.1) from Mycobacterium tuberculosis, encoded by the gene Rv3273 (mtCA 3), was investigated using a panel of natural and non-natural amino acids and amines. mtCA 3 was effectively activated by D-DOPA, L-Trp, dopamine and serotonin, with KAs ranging between 8.98 and 12.1 µM. L-His and D-Tyr showed medium potency activating effects, with KAs in the range of 17.6-18.2 µM, whereas other amines and amino acids were relatively ineffective activators, with KAs in the range of 28.9-52.2 µM. As the physiological roles of the three mtCAs present in this pathogen are currently poorly understood and considering that inhibition of these enzymes has strong antibacterial effects, discovering molecules that modulate their enzymatic activity may lead to a better understanding of the factors related to the invasion and colonisation of the host during Mycobacterium tuberculosis infection.

Activation studies of the α- and β-carbonic anhydrases from the pathogenic bacterium Vibrio cholerae with amines and amino acids

The α- and β-class carbonic anhydrases (CAs, EC 4.2.1.1) from the pathogenic bacterium Vibrio cholerae, VchCAα, and VchCAβ, were investigated for their activation with natural and non-natural amino acids and amines. The most effective VchCAα activators were L-tyrosine, histamine, serotonin, and 4-aminoethyl-morpholine, which had KAs in the range of 8.21-12.0 µM. The most effective VchCAβ activators were D-tyrosine, dopamine, serotonin, 2-pyridyl-methylamine, 2-aminoethylpyridine, and 2-aminoethylpiperazine, which had KAs in the submicromolar - low micromolar range (0.18-1.37 µM). The two bacterial enzymes had very different activation profiles with these compounds, between each other, and in comparison to the human isoforms hCA I and II. Some amines were selective activators of VchCAβ, including 2-pyridylmethylamine (KA of 180 nm for VchCAβ, and more than 20 µM for VchCAα and hCA I/II). The activation of CAs from bacteria, such as VchCAα/β has not been considered previously for possible biomedical applications. It would be of interest to study in more detail the extent that CA activators are implicated in the virulence and colonisation of the host by such pathogenic bacteria, which for Vibrio cholerae, is highly dependent on the bicarbonate concentration and pH in the surrounding tissue.

Activation of β- and γ-carbonic anhydrases from pathogenic bacteria with tripeptides

Six tripeptides incorporating acidic amino acid residues were prepared for investigation as activators of β- and γ-carbonic anhydrases (CAs, EC 4.2.1.1) from the pathogenic bacteria Vibrio cholerae, Mycobacterium tuberculosis, and Burkholderia pseudomallei. The primary amino acid residues that are involved in the catalytic mechanisms of these CA classes are poorly understood, although glutamic acid residues near the active site appear to be involved. The tripeptides that contain Glu or Asp residues can effectively activate VchCAβ and VchCAγ (enzymes from V. cholerae), Rv3273 CA (mtCA3, a β-CA from M. tuberculosis) and BpsCAγ (γ-CA from B. pseudomallei) at 0.21-18.1 µM levels. The position of the acidic residues in the peptide sequences can significantly affect bioactivity. For three of the enzymes, tripeptides were identified that are more effective activators than both l-Glu and l-Asp. The tripeptides are also relatively selective because they do not activate prototypical α-CAs (human carbonic anhydrases I and II). Because the role of CA activators in the pathogenicity and life cycles of these infectious bacteria are poorly understood, this study provides new molecular probes to explore such processes.

Discovery of novel 1,3-diaryltriazene sulfonamides as carbonic anhydrase I, II, VII, and IX inhibitors

A series of new 1,3-diaryltriazene sulfonamides was synthesised by reaction of diazonium salt of metanilamide (3-aminobenzene sulfonamide) with substituted aromatic amines. The obtained new compounds were assayed as inhibitors of four physiologically and pharmacologically relevant human (h) isoforms of carbonic anhydrases (CA, EC 4.2.1.1), specifically, hCA I, hCA II, and hCA VII (cytosolic isoforms), as well as the tumour-associated membrane-bound isoform hCA IX. All isoforms investigated here were inhibited by the newly synthesised 1,3-diaryltriazene sulfonamide derivatives from the micromolar to the nanomolar range. The cytosolic isoforms were inhibited with K_is in the range of 92.3–8371.1 nM (hCA I), 4.3–9194.0 nM (hCA II), and 15.6–9477.8 nM (hCA VII), respectively. For the membrane-bound tumour-associated isoform hCA IX, the K_I-s ranged between 50.8 and 9268.5 nM. The structure–activity relationship (SAR) with these newly synthesised metanilamide derivatives are discussed in detail.

Dioxygen, an unexpected carbonic anhydrase ligand

Carbonic anhydrases (CAs, EC 4.2.1.1) are ubiquitous metalloenzymes, grouped into seven different classes, which catalyze the reaction of CO₂ hydration to bicarbonate and protons. All of the fifteen human isoforms reported to date belong to the α-class and contain zinc as a cofactor. The structure of human Zn,Cu-CA II has been solved which contains a copper ion bound at its N-terminal, coordinated to His4 and His64. In the active site a dioxygen molecule is coordinated to the zinc ion. Since dioxygen is a rather unexpected CA ligand, molecular dynamics (MD) simulations were performed which suggested a superoxide character of the zinc bound O₂.

The first activation studies of the η-carbonic anhydrase from the malaria parasite Plasmodium falciparum with amines and amino acids

The first activation study of a η-class carbonic anhydrase (CAs, EC 4.2.1.1) is reported. A panel of 24 natural and non-natural amino acids and amines was used to explore the activation profile of Plasmodium falciparum CA (PfACA). The most effective activators belonged to the amino acid chemotype, with d-Glu, l-Asp, l-/d-Phe and l-/d-DOPA possessing activation constant in the range of 82 nM-0.75 µM, whereas l-/d-His, l-Tyr, 4-amino-l-Phe and l-Gln were slightly less effective (K_A in the range of 1.00-2.51 µM. The only amine with submicromolar activating properties was 1-(2-aminoethyl-piperazine) with a K_A of 0.71 µM, whereas histamine, dopamine and serotonin showed K_A ranging between 7.18 and 9.97 µM. As CA activators have scarcely been investigated for their interaction with protozoan CAs, this study may be relevant for an improved understanding of the role of this enzyme in the life cycle of the malaria producing organisms belonging to the genus Plasmodium.

The zinc - but not cadmium - containing ζ-carbonic from the diatom Thalassiosira weissflogii is potently activated by amines and amino acids

The activation of the ζ-class carbonic anhydrase (CAs, EC 4.2.1.1) from the diatom Thalassiosira weissflogii (TweCAζ) incorporating both Zn(II) and Cd(II) at the active site, was investigated for the first time, using a panel of natural and non-natural amino acids and amines. CdTweCAζ was completely insensitive to activation, whereas all these compounds were effective activators of the zinc-containing enzyme ZnTweCAζ, with activation constants ranging between 92 nM and 37.9 µM. The most effective ZnTweCAζ activators were l-adrenaline, 1-(2-aminoethyl)-piperazine and 4-(2-aminoethyl)-morpholine, with K_As in the range of 92-150 nM. l-His, l- and d-Tyr and some pyridyl-alkylamines, had K_As in the range of 0.62-0.98 µM, whereas l-/d-DOPA, d-Trp, histamine, serotonin and l-Asn were the next most efficient activators, with K_As in the range of 1.27-3.19 µM. The least effective activators were l-Phe (K_A of 15.4 µM) and l-Asp (K_A of 37.9 µM). This in vitro study may be useful for a more complete understanding of the activation processes of various CA enzyme families, of which the ζ-class was scarcely investigated.

The first activation study of a δ-carbonic anhydrase: TweCAδ from the diatom Thalassiosira weissflogii is effectively activated by amines and amino acids

The activation of the δ-class carbonic anhydrase (CAs, EC 4.2.1.1) from the diatom Thalassiosira weissflogii (TweCAδ) was investigated using a panel of natural and non-natural amino acids and amines. The most effective activator of TweCAδ was d-Tyr (K_A of 51 nM), whereas several other amino acids and amines, such as L-His, L-Trp, d-Trp, dopamine and serotonin were submicromolar activators (K_As from 0.51 to 0.93 µM). The most ineffective activator of TweCAδ was 4-amino-l-Phe (18.9 µM), whereas d-His, l-/d-Phe, l-/d-DOPA, l-Tyr, histamine, some pyridyl-alkylamines, l-adrenaline and aminoethyl-piperazine/morpholine were moderately potent activators (K_As from 1.34 to 8.16 µM). For any δ-CA, there are no data on the crystal structure, homology modelling and the amino acid residues that are responsible for proton transfer to the active site are currently unknown making it challenging to provide a detailed rational for these findings. However, these data provide further evidence that this class of underexplored CA deserves more attention.

Activation studies with amines and amino acids of the β-carbonic anhydrase from the pathogenic protozoan Leishmania donovani chagasi

The activation of a β-class carbonic anhydrase (CAs, EC 4.2.1.1) from Leishmania donovani chagasi (LdcCA) was investigated using a panel of natural and non-natural amino acids and amines. The most effective activators belonged to the amine class, with histamine, dopamine, serotonin, 2-pyridyl-methylamine and 4-(2-aminoethyl)-morpholine with activation constants in the range of 0.23-0.94 µM. In addition, 2-(2-aminoethyl)pyridine and 1-(aminoethyl)-piperazine were even more effective activators (K_As of 9-12 nM). Amino acids such as L-/D-His, L-/D-Phe, L-/D-DOPA, L-/D-Trp and L-/D-Tyr were slightly less effective activators compared to the amines, but showed activation constants in the low micromolar range (1.27-9.16 µM). Many of the investigated activators are autacoids that are present in rather high concentrations in different tissues of the host mammals infected by these parasites. As CA activators have not yet been investigated for protozoan CAs, this study may be relevant for an improved understanding of the role of this enzyme in the life cycle of Leishmania.

Carbonic anhydrase activators

Mammalian carbonic anhydrases (CAs; EC 4.2.1.1) of which 16 isoforms are known, are involved in important physiological functions. Their inhibition is exploited pharmacologically for the treatment of many diseases (glaucoma, edema, epilepsy, obesity, hypoxic tumors, neuropathic pain, etc.) but the activators were less investigated till recently. A review on the CA activation is presented, with the activation mechanism, drug design approaches of activators and comparison of the various isoforms activation profiles being discussed. Some CAs, which are abundant in the brain, were recently demonstrated to be activatable by drug-like compounds, affording the possibility to design agents that enhance cognition, with potential therapeutic applications in aging and neurodegenerative diseases as well as tissue engineering.

Synthesis and biological evaluation of novel N,N'-diaryl cyanoguanidines acting as potent and selective carbonic anhydrase II inhibitors

A series of novel N,N''-diaryl cyanoguanidines were synthesized by reacting diphenyl N-cyanocarbonimidate with sulfanilamide followed by treatment of the obtained cyano-O-phenylisourea with substituted aromatic amines. The newly prepared N,N''-diaryl cyanoguanidines showed a very interesting inhibition profile against four selected human carbonic anhydrase (CA, EC 4.2.1.1) isoforms, hCA I and hCA II (cytosolic), hCA IV (membrane-bound), and hCA IX (transmembrane). All these compounds showed a potent inhibition against isoform hCA II,with inhibition constants in the low nanomolar range, as well as a high selectivity for hCA II over hCA I, IV and IX. Since hCA II is an important drug target for antiglaucoma agents, these isoform-selective inhibitors may be considered of interest for further medicinal/pharmacologic studies.

The γ-carbonic anhydrase from the pathogenic bacterium Vibrio cholerae is potently activated by amines and amino acids

The γ-class carbonic anhydrase (CAs, EC 4.2.1.1) from the pathogenic bacterium Vibrio cholerae, VchCAγ, was investigated for its activation with a panel of natural and non-natural amino acids and amines. The enzyme was effectively activated by l-tryptophan, 1-(2-minoethyl)-piperazine and 4-(2-aminoethyl)-morpholine, in the low nanomolar range (K_As 8-71 nM). In contrast, l-/d-Phe, l-/d-DOPA, d-Trp, l-/d-Tyr, 4-amino-l-Phe, histamine, dopamine, serotonin, some pyridyl-alkylamines, as well as l-adrenaline were submicromolar activators (K_As between 0.10 and 0.73 µM). l- and d-His were the least effective VchCAγ activators (K_As of 1.01-14.2 µM). The activation of CAs from bacteria have not been considered to date for possible biomedical applications. It would be of interest to study in more details the role of CA activators in processes connected with the virulence and colonization of the host by pathogenic bacteria, such as Vibrio cholerae, which is highly dependent on the concentration of bicarbonate in tissues.

Activation Profile Analysis of CruCA4, an α-Carbonic Anhydrase Involved in Skeleton Formation of the Mediterranean Red Coral, Corallium rubrum

CruCA4, a coral α-carbonic anhydrase (CA, EC 4.2.1.1) involved in the biomineralization process of the Mediterranean red coral, Corallium rubrum, was investigated for its activation with a panel of amino acids and amines. Most compounds showed considerable activating properties, with a rather well defined structure-activity relationship. The most effective CruCA4 activators were d-His, 4-H₂N-l-Phe, Histamine, Dopamine, Serotonin, 1-(2-Aminoethyl)-piperazine, and l-Adrenaline, with activation constants in the range of 8-98 nM. Other amines and amino acids, such as d-DOPA, l-Tyr, 2-Pyridyl-methylamine, 2-(2-Aminoethyl) pyridine and 4-(2-Aminoethyl)-morpholine, were submicromolar CruCA4 activators, with K_A ranging between 0.15 and 0.93 µM. Since it has been shown that CA activators may facilitate the initial phases of in-bone mineralization, our study may be relevant for finding modulators of enzyme activity, which can enhance the formation of the red coral skeleton.

Five- and Six-Membered Nitrogen-Containing Compounds as Selective Carbonic Anhydrase Activators

It has been proven that specific isoforms of human carbonic anhydrase (hCA) are able to fine-tune physiological pathways connected to signal processing, and that decreased CAs expression negatively influences cognition, leading to mental retardation, Alzheimer's disease, and aging-related cognitive dysfunctions. For this reason, a small library of natural and synthetic nitrogen containing cyclic derivatives was assayed as activators of four human isoforms of carbonic anhydrase (hCA I, II, IV and VII). Most of the compounds activated hCA I, IV and VII in the micromolar range, with K_As ranging between 3.46 and 80.5 μM, whereas they were not active towards hCA II (K_As > 100 μM). Two natural compounds, namely l-(+)-ergothioneine (1) and melatonin (2), displayed K_As towards hCA VII in the nanomolar range after evaluation by a CO₂ hydration method in vitro, showing a rather efficient and selective activation profile with respect to histamine, used as a reference compound. Corroborated with the above in vitro findings, a molecular modelling in silico approach has been performed to correlate these biological data, and to elucidate the binding interaction of these activators within the enzyme active site.