Deciphering the Mechanism of Human Carbonic Anhydrases Inhibition with Sulfocoumarins: Computational and Experimental Studies

Sulfonamide-incorporated bis(α-aminophosphonates) as promising carbonic anhydrase inhibitors: Design, synthesis, biological evaluation, and X-ray crystallographic studies

A novel series of sulfonamide-incorporated bis(α-aminophosphonates) acting as effective carbonic anhydrase (CA, EC 4.2.1.1) inhibitors is reported. The synthesized bivalent ligands were tested against five human (h) isoforms, hCA I, hCA II, hCA VII, hCA IX, and hCA XIII. Such derivatives showed high activity and selectivity against the cancer-related, membrane-bound isoform hCA IX, and among them, compound 5h, tetraisopropyl (1,3-phenylenebis{[(4-sulfamoylphenyl)amino]methylene})bis(phosphonate) showed a KI of 15.1 nM, being highly selective against this isoform over all other investigated ones (hCA I/IX = 42; hCA II/IX = 6, hCA VII/IX = 3, hCA XIII/IX = 5). Therefore, compound 5h could be a potential lead for the development of selective anticancer agents. The newly developed sulfonamides were also found effective inhibitors against the cytosolic hCA XIII isoform. Compound 5i displayed the best inhibition against this isoform with a KI of 17.2 nM, equal to that of the well-known inhibitor acetazolamide (AAZ), but significantly more selective over all other tested isoforms (hCA I/XIII = 239; hCA II/XIII = 23, hCA VII/XIII = 2, hCA IX/XIII = 3) compared to AAZ.

Derivatives of 4-methyl-1,2,3-benzoxathiazine 2,2-dioxide as selective inhibitors of human carbonic anhydrases IX and XII over the cytosolic isoforms I and II

A series of 4-methyl-1,2,3-benzoxathiazine-2,2-dioxides with various substituents in 5, 6 or 7 positions was obtained from corresponding 2'-hydroxyacetophenones in their reaction with sulphamoyl chloride. 6- and 7-aryl substituted 4-methyl-1,2,3-benzoxathiazine-2,2-dioxides were obtained from aryl substituted 2'-hydroxyacetophenonesprepared from 4- or 5-bromo-2'-hydroxyacetophenones via two-step protocol. 4-Methyl-1,2,3-benzoxathiazine-2,2-dioxides were investigated as inhibitors of four human (h) carbonic anhydrase (hCA, EC 4.2.1.1) isoforms, off-target cytosolic hCA I and II, and target transmembrane, tumour-associated hCA IX and XII. Twenty derivatives of 4-methyl-1,2,3-benzoxathiazine 2,2-dioxide were obtained. With one exception (compound2a), they mostly act as nanomolar inhibitors of target hCA IX and XII. Basically, all screened compounds express none or low inhibitory properties towards off-target hCA I. hCA II is inhibited in micromolar range. Overwhelming majority of 4-methyl-1,2,3-benzoxathiazine 2,2-dioxides express excellent selectivity towards CA IX/XII over hCA I as well as very good selectivity towards CA IX/XII over hCA II.

POCl3 mediated one-pot deoxygenative aromatization and electrophilic chlorination of dihydroxy-2-methyl-4-oxo-indeno[1,2-b]pyrroles

A class of indenopyrroles is presented by the treatment of known dihydroxy-2-methyl-4-oxoindeno[1,2-b]pyrroles with phosphorus oxychloride (POCl₃). The elimination of vicinal hydroxyl groups at the 3a and 8b positions, formation of a π bond, and electrophilic chlorination of the methyl group attached to C² resulted in the fused aromatic pyrrole structures. Benzylic substitution of various nucleophiles such as H₂O, EtOH, and NaN₃ with a chlorine atom gave diverse 4-oxoindeno[1,2-b]pyrrole derivatives in 58 to 93% yields. The reaction was investigated in different aprotic solvents, and the highest reaction yield was obtained in DMF. The structures of the products were confirmed by spectroscopic methods, elemental analysis, and X-ray crystallography.

Inhibition Studies on Human and Mycobacterial Carbonic Anhydrases with N-((4-Sulfamoylphenyl)carbamothioyl) Amides

A library of structurally diverse N-((4-sulfamoylphenyl)carbamothioyl) amides was synthesized by selective acylation of easily accessible 4-thioureidobenzenesulfonamide with various aliphatic, benzylic, vinylic and aromatic acyl chlorides under mild conditions. Inhibition of three α-class cytosolic human (h) carbonic anhydrases (CAs) (EC 4.2.1.1); that is, hCA I, hCA II and hCA VII and three bacterial β-CAs from Mycobacterium tuberculosis (MtCA1-MtCA3) with these sulfonamides was thereafter investigated in vitro and in silico. Many of the evaluated compounds displayed better inhibition against hCA I (K_I = 13.3-87.6 nM), hCA II (K_I = 5.3-384.3 nM), and hCA VII (K_I = 1.1-13.5 nM) compared with acetazolamide (AAZ) as the control drug (K_I values of 250, 12.5 and 2.5 nM, respectively, against hCA I, hCA II and hCA VII). The mycobacterial enzymes MtCA1 and MtCA2 were also effectively inhibited by these compounds. MtCA3 was, on the other hand, poorly inhibited by the sulfonamides reported here. The most sensitive mycobacterial enzyme to these inhibitors was MtCA2 in which 10 of the 12 evaluated compounds showed K_Is (K_I, the inhibitor constant) in the low nanomolar range.

Investigation of carbonic anhydrase inhibitory potency of (Z/E)-alkyl N'-benzyl-N-(arylsulfonyl)-carbamimidothioates

Aim: Among 15 human (h) carbonic anhydrase (CA; EC 4.2.1.1) isoforms, two (hCA IX and XII) play important roles in the growth and survival of tumor cells, making them therapeutic targets for cancer treatment. This study aimed to develop novel sulfonamide-based compounds as selective hCA IX and XII inhibitors. Materials & methods: A library of novel N-sulfonyl carbamimidothioates was obtained for CA inhibitory activity studies against four hCA isoforms. Results: None of the developed compounds displayed inhibitory potential against off-target isoforms hCA I and II. However, they effectively inhibited tumor-associated hCA IX and XII. Conclusion: The present study suggests potent lead compounds as selective hCA IX and XII inhibitors with anticancer activity.

Inhibition Studies on Carbonic Anhydrase Isoforms I, II, IX, and XII with a Series of Sulfaguanidines

Two novel sulfaguanidine series, six N-(N,N'-dialkyl/dibenzyl-carbamimidoyl) benzenesulfonamide derivatives and nine N-(N-alkyl/benzyl-carbamimidoyl) benzenesulfonamide derivatives, were obtained by desulfidative amination of easily accessible dimethyl arylsulfonylcarbonimidodithioates under catalyst- and base-free conditions. The newly synthesized compounds were tested for the inhibition of four different isozymes of human carbonic anhydrase (hCA I, II, IX and XII, EC 4.2.1.1). Both series reported here were inactive against the off-target isozymes hCA I and II (K_i >100 μM). Interestingly, all investigated compounds inhibited both target isozymes hCA IX and XII in the submicromolar to micromolar ranges in which K_i values spanned from 0.168 to 0.921 μM against hCA IX and from 0.335 to 1.451 μM against hCA XII. The results indicated that N-(N-alkyl/benzyl-carbamimidoyl) benzenesulfonamides were slightly more potent inhibitors than N-(N,N'-dialkyl/dibenzyl-carbamimidoyl) benzenesulfonamides. Among the evaluated compounds, N-n-octyl-substituted N-carbamimidoylbenzenesulfonamide showed the most significant activity with a K_i value of 0.168 μM against hCA IX, which was four-fold more selective toward this isozyme versus hCA XII. Again, another derivative from N-(N-alkyl/benzyl-carbamimidoyl) benzenesulfonamide series, N-p-methylbenzyl-substituted N-carbamimidoylbenzenesulfonamide, demonstrated superior inhibitory activity against hCA XII with a K_i value of 0.335 μM.

Benzenesulfonamides with trisubstituted triazole motif as selective carbonic anhydrase I, II, IV, and IX inhibitors

Twenty novel 1,2,3-triazole benzenesulfonamides featuring nitrile 8a-g, carbothioamide 9a-f, and N'-hydroxycarboximidamide 10a-g functionalities were designed and synthesized to improve potency and selectivity as carbonic anhydrase inhibitors (CAIs). The synthesized 1,2,3-triazole compounds were tested in vitro as CAIs against four physiologically and pharmacologically relevant isoforms of human carbonic anhydrase (hCA I, II, IV, and IX). Compounds 8a-g, 9a-f, and 10a-g displayed variable inhibition constants ranging from 8.1 nM to 3.22 μM for hCA I, 4.7 nM to 0.50 μM for hCA II, 15.0 nM to 3.7 μM for hCA IV, and 29.6 nM to 0.27 μM for hCA IX. As per the inhibition data profile, compounds 9a-e exhibited strong efficacy for hCA IV, whereas the inhibition was found to be somewhat diminished in the case of hCA IX by nearly all the compounds. A computational protocol based on docking and MM-GBSA was conducted to reveal the plausible interactions of the targeted sulfonamides within the hCA II and IX binding sites. The outcomes of appending various functionalities at the C-4 position of the 1,2,3-triazole motif over the inhibition potential and selectivity of the designed sulfonamides were examined with a potential for the discovery of new isoform selective CAIs. The CAI and SAR data established the significance of the synthesized 1,2,3-triazoles as building blocks for developing CAI drugs.

Continued Structural Exploration of Sulfocoumarin as Selective Inhibitor of Tumor-Associated Human Carbonic Anhydrases IX and XII

A series of new 3- and 7-substituted sulfocoumarins was obtained by several cyclization reactions and subsequent derivatization for screening as prodrug inhibitors of the human (h) cancer-associated carbonic anhydrases (CAs) IX and XII. All products were ineffective inhibitors against the off-target hCA I and II, whilst hCAs IX and XII were inhibited with inhibition constants (KIs) spanning from low nanomolar to the high micromolar range, according to the sulfocoumarin derivatization pattern. In particular, sulfocoumarin 15 turned out to be the most potent and selective inhibitor herein reported (hCA I and II: KI > 100 µM; hCA IX: KI = 22.9 nM; hCA XII: KI = 19.2 nM). Considering that hCA IX and XII validated anti-tumor targets, such prodrug, isoform-selective inhibitors as the sulfocoumarins reported here may be useful for identifying suitable drug candidates for clinical trials.

Synthesis, molecular modelling and QSAR study of new N-phenylacetamide-2-oxoindole benzensulfonamide conjugates as carbonic anhydrase inhibitors with antiproliferative activity

In continuation of our previous studies to optimise potent carbonic anhydrase inhibitors, two new series of isatin N-phenylacetamide based sulphonamides were synthesised and screened for their human (h) carbonic anhydrase (EC 4.2.1.1) inhibitory activities against four isoforms hCA I, hCA II, hCA IX and hCA XII. The indole-2,3-dione derivative 2h showed the most effective inhibition profile against hCAI and hCA II (K_I = 45.10, 5.87 nM) compared to acetazolamide (AAZ) as standard inhibitor. Moreover, 2h showed appreciable inhibition activity against the tumour-associated hCA XII, similar to AAZ showing K_I of 7.91 and 5.70 nM, respectively. The analogs 3c and 3d showed good cytotoxicity effects, and 3c revealed promising selectivity towards lung cell line A549. Molecular docking was carried out for 2h and 3c to predict their binding conformations and affinities towards the hCA I, II, IX and XII isoforms.

Binding site comparison for coumarin inhibitors and amine/amino acid activators of human carbonic anhydrases

The first structural analysis comparing the binding mode to the target carbonic anhydrases (CAs, EC 4.2.1.1) of two opposite classes of modulators is presented here: coumarin derivatives act as prodrug CA inhibitors (CAIs), being hydrolyzed by the enzyme esterase activity to 2-hydroxycinnamic acids that occlude the active site entrance; CA activators (CAAs) belonging of the amine and amino acid types, enhance the CA activity by increasing the efficiency of the rate-determining proton shuttling step in the CA catalytic cycle. Analysis of the crystallographic data available for the human CA isoform II in adduct with two coumarin CAIs and some CAAs showed that both types of CA modulators bind in the same region of the enzyme active site, basically interacting with superimposable amino acid residues, that are Trp5, Asn62, His64, Asn67, Gln92, Thr200. A plethora of water molecules also participate in the adducts formation. This structural analysis showed that presence of certain chemical groups in the compound structure is mandatory to produce an activating rather than inhibitory action, such as multiple nitrogen- and oxygen-based moieties capable of shuttling protons or forming extended H-bond networks nearby the proton shuttle residue. This constitutes the only known example among all enzymes of an identical binding site for inhibitors and activators, which, in addition, possess significant pharmacological applications.

Ureidosulfocoumarin Derivatives As Selective and Potent Carbonic Anhydrase IX and XII Inhibitors

Owing to severe allergic reactions (anaphylaxis) and resistance exhibited by sulfonamide-based carbonic anhydrase (CA) inhibitors, non-classical or non-sulfonamide CA inhibitors are gaining increased attention by medicinal chemists. In this context, we report the design and synthesis of 30 new non-sulfonamide sulfocoumarin derivatives as CA inhibitors. They were investigated against hCA I and II (cytosolic isozymes) as well as hCA IX and XII (transmembrane, tumor-associated enzymes). All compounds showed prominent selectivity for the tumor-associated isoenzymes hCA IX and XII over the cytosolic isoenzymes hCA I and II. Among all synthesized compounds, 1-(2,2-dioxidobenzo[e][1,2]oxathiin-6-yl)-3-(o-tolyl)urea(5 j)and1-(3-fluorophenyl)-3-(8-methoxy-2,2-dioxidobenzo[e][1,2]oxathiin-6-yl)urea(5 q)were found to be more potent and to have better inhibition constant values against hCA IX than the standard acetazolamide (AAZ), with K_i values of 23.6 and 23.3 nM, respectively. All other compounds were found to be active under K_i =920 nM against hCA IX and XII.This study provides a new perspective for the future development of non-sulfonamide derivatives as selective CA inhibitors.

Substitution Effect on 2-(Oxazolinyl)-phenols and 1,2,5-Chalcogenadiazole-Annulated Derivatives: Emission-Color-Tunable, Minimalistic Excited-State Intramolecular Proton Transfer (ESIPT)-Based Luminophores

Minimalistic 2-(oxazolinyl)-phenols substituted with different electron-donating and -withdrawing groups as well as 1,2,5-chalcogenadiazole-annulated derivatives thereof were synthesized and investigated in regard to their emission behavior in solution as well as in the solid state. Depending on the nature of the incorporated substituent and its position, emission efficiencies were increased or diminished, resulting in AIE or ACQ characteristics. Single-crystal analysis revealed J- and H-type packing motifs and a so-far undescribed isolation of ESIPT-based fluorophores in the keto form.

The antibiotic furagin and its derivatives are isoform-selective human carbonic anhydrase inhibitors

The clinically used antibiotic Furagin and its derivatives possess inhibitory activity on human (h) carbonic anhydrases (CA, EC 4.2.1.1), some of which are highly expressed in various tissues and malignancies (hCA IX/XII). Furagin exhibited good hCA IX and XII inhibition with K_Is of 260 and 57 nM, respectively. It does not inhibit off-target CA I and poorly inhibited CA II (K_I = 9.6 μM). Some synthesised Furagin derivatives with aminohydantoin moieties as zinc binding group exhibited weak inhibition of CA I/II, and good inhibition of CA IX/XII with K_Is ranging from 350 to 7400 and 150 to 5600 nM, respectively. Docking and molecular dynamics simulations suggest that selectivity for the cancer-associated CA IX/XII over CA II is due to strong H-bond interactions in CA IX/XII, involving the tail orientated towards hydrophobic area of the active site. These results suggest a possible drug repurposing of Furagin as anti-cancer agent.

Bioorganometallic derivatives of 4-hydrazino-benzenesulphonamide as carbonic anhydrase inhibitors: synthesis, characterisation and biological evaluation

A series of bio-organometallic-hydrazones of the general formula [{(η5-C5H4)-C(R)=N-N(H)-C6H4-4-SO2NH2}]MLn(MLn = Re(CO)3, Mn(CO)3, FeCp; R=H, CH3) were prepared by reaction of formyl/acetyl organometallic precursors with 4-hydrazino-benzenesulphonamide. All compounds were characterized by conventional spectroscopic techniques (infra-red, 1H and 13C NMR, mass spectrometry and elemental analysis). Biological evaluation as carbonic anhydrase (CA, EC 4.2.1.1) inhibitors agents was carried out using four human/h) isoforms, hCA I, II, IX and XII. The cytosolic isoforms hCA I and II were effectively inhibited by almost all derivatives with inhibition constants of 1.7-22.4 nM. Similar effects were observed for the tumour-associated transmembrane isoform hCA XII (KIs of 1.9-24.4 nM). hCA IX was less sensitive to inhibition with these compounds. The presence of bio-organometallic or metallo-carbonyl moieties in the molecules of these CAIs makes them amenable for interesting pharmacologic applications, for example for compounds with CO donating properties.

Ninhydrins inhibit carbonic anhydrases directly binding to the metal ion

Ninhydrins show extensive application in organic chemistry and agriculture whereas they have been poorly investigated as bioactive molecules for medicinal chemistry purposes. A series of ninhydrin derivatives was here investigated for the inhibition of human carbonic anhydrases (CAs, EC 4.2.1.1), based on earlier evidence that gem diols are able to coordinate the metal ion from the CA active site. Ninhydrins demonstrated a micromolar inhibitory action against CA I and IX (K_Is in the range 0.57-68.2 μM) and up to a nanomolar efficacy against CA II and VII (K_Is in the range 0.025-78.2 μM), validated isoforms as targets in several CNS-related diseases. CA IV was instead weakly or poorly inhibited. A computational protocol based on docking, MM-GBSA and metadynamics calculations was used to elucidate the putative binding mode of this type of inhibitors to CA II and CA VII. The findings of this study testify that such pharmacologically underestimated ligands may represent interesting lead compounds for the development of CA inhibitors possessing an innovative mechanism of action, i.e., mono- or bis-coordination to the zinc ion through the diol moiety.

Synthesis, Computational Studies and Assessment of in Vitro Activity of Squalene Derivatives as Carbonic Anhydrase Inhibitors

We report novel molecules incorporating the nontoxic squalene scaffold and different carbonic anhydrase inhibitors (CAIs). Potent inhibitory action, in the low-nanomolar range, was detected against isoforms hCA II for sulfonamide derivatives, which proved to be selective against this isoform over the tumor-associate hCA IX and XII isoforms. On the other hand, coumarin derivatives showed weak potency but high selectivity against the tumor-associated isoform CA IX. These compounds are interesting candidates for preclinical evaluation in glaucoma or various tumors in which the two enzymes are involved. In addition, an in silico study of inhibitor-bound hCA II revealed extensive interactions with the hydrophobic pocket of the active site and provided molecular insights into the binding properties of these new inhibitors.

Discovery of first-in-class multi-target adenosine A2A receptor antagonists-carbonic anhydrase IX and XII inhibitors. 8-Amino-6-aryl-2-phenyl-1,2,4-triazolo [4,3-a]pyrazin-3-one derivatives as new potential antitumor agents

This paper describes identification of the first-in-class multi-target adenosine A_2A receptor antagonists-carbonic anhydrase (CA) IX and XII inhibitors, as new potential antitumor agents. To obtain the multi-acting ligands, the 8-amino-2,6-diphenyltriazolo[4,3-a]pyrazin-3-one, a potent adenosine hA_2A receptor (AR) antagonist, was taken as lead compound. To address activity against the tumor-associated CA isoforms, it was modified by introduction of different substituents (OH, COOH, CONHOH, SO₂NH₂) on the 6-phenyl ring or on a phenyl pendant connected to the former through different spacers. Among the new triazolopyrazines 1-23, the most active were those featuring the sulfonamide residue. Derivative 20, featuring a 4-sulfonamidophenyl residue attached through a CONH(CH₂)₂CONH spacer at the para-position of the 6-phenyl ring, showed the best combination of activity at the three targets. In fact, it inhibited both the tumor-associated hCA IX and XII isozymes at nanomolar concentration (K_i = 5.0 and 27.0 nM), and also displayed a quite good affinity for the hA_2A AR (K_i = 108 nM). Compound 14, bearing the 4-sulfonamidophenyl residue linked at the para-position of the 6-phenyl ring by a CONH spacer, was remarkable because both its hA_2A AR affinity and hCA XII inhibitory potency were in the low nanomolar range (K_i = 6.4 and 6.2 nM, respectively). Molecular docking studies highlighted the interaction mode of selected triazolopyrazines in the hA_2A AR recognition pocket and in the active site of hCA II, IX and XII isoforms.

Development of oxathiino[6,5-b]pyridine 2,2-dioxide derivatives as selective inhibitors of tumor-related carbonic anhydrases IX and XII

Oxathiino[6,5-b]pyridine 2,2-dioxides are identified as a new class of isoform-selective nanomolar inhibitors of tumor associated human carbonic anhydrases (hCA) IX and XII. At the same time they do not inhibit or poorly inhibit cytosolic isoforms hCA I and II. Oxathiino[6,5-b]pyridine 2,2-dioxides exhibited good antiproliferative properties on tumor cell lines MCF-7 (Human breast adenocarcinoma), A549 (human lung (alveolar) adenocarcinoma) and HeLa (epithelioid cervix carcinoma).

Aryl-4,5-dihydro-1H-pyrazole-1-carboxamide Derivatives Bearing a Sulfonamide Moiety Show Single-digit Nanomolar-to-Subnanomolar Inhibition Constants against the Tumor-associated Human Carbonic Anhydrases IX and XII

A series of new 3-phenyl-5-aryl-N-(4-sulfamoylphenyl)-4,5-dihydro-1H-pyrazole-1-carboxamide derivatives was designed here, synthesized, and studied for carbonic anhydrase (CAs, EC 4.2.1.1) inhibitory activity against the human (h) isozymes I, II, and VII (cytosolic, off-target isoforms), and IX and XII (anticancer drug targets). Generally, CA I was not effectively inhibited, whereas effective inhibitors were identified against both CAs II (K_Is in the range of 5.2–233 nM) and VII (K_Is in the range of 2.3–350 nM). Nonetheless, CAs IX and XII were the most susceptible isoforms to this class of inhibitors. In particular, compounds bearing an unsubstituted phenyl ring at the pyrazoline 3 position showed 1.3–1.5 nM K_Is against CA IX. In contrast, a subset of derivatives having a 4-halo-phenyl at the same position of the aromatic scaffold even reached subnanomolar K_Is against CA XII (0.62–0.99 nM). Docking studies with CA IX and XII were used to shed light on the derivative binding mode driving the preferential inhibition of the tumor-associated CAs. The identified potent and selective CA IX/XII inhibitors are of interest as leads for the development of new anticancer strategies.

Exploring the multiple binding modes of inhibitors to carbonic anhydrases for novel drug discovery

INTRODUCTION

The spacious active site cavity of the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1) shows a great versatility for a variety of binding modes for modulators of activity, inhibitors, and activators, some of which are clinically used drugs.

AREAS COVERED

There are at least four well-documented CA inhibition mechanisms and the same number of binding modes for CA inhibitors (CAIs), one of which superposes with the binding of activators (CAAs). They include (i) coordination to the catalytic metal ion; (ii) anchoring to the water molecule coordinated to the metal ion; (iii) occlusion of the active site entrance; and (iv) binding outside the active site. A large number of chemical classes of CAIs show these binding modes explored in detail by kinetic, crystallographic, and other techniques. The tail approach was applied to all of them and allowed many classes of highly isoform-selective inhibitors. This is the subject of our review.

EXPERT OPINION

All active site regions of CAs accommodate inhibitors to bind, which is reflected in very different inhibition profiles for such compounds and the possibility to design drugs with effective action and new applications, such as for the management of hypoxic tumors, neuropathic pain, cerebral ischemia, arthritis, and degenerative disorders.

Perfluoroalkyl Substances of Significant Environmental Concern Can Strongly Inhibit Human Carbonic Anhydrase Isozymes

Perfluoroalkyl substances (PFASs) persist and are ubiquitous in the environment. The origins of PFAS toxicity and how they specifically affect the functions of proteins remain unclear. Herein, we report that PFASs can strongly inhibit the activity of human carbonic anhydrases (hCAs), which are ubiquitous enzymes that catalyze the hydration of CO₂, are abundant in the blood and organs of mammals, and involved in pH regulation, ion homeostasis, and biosynthesis. The interactions between PFASs and hCAs were investigated using stopped-flow kinetic enzyme-inhibition measurements, native mass spectrometry (MS), and ligand-docking simulations. Narrow-bore emitters in native MS with inner diameters of ∼300 nm were used to directly and simultaneously measure the dissociation constants of 11 PFASs to an enzyme, which was not possible using conventional emitters. The data from native MS and stopped-flow measurements were in excellent agreement. Of 15 PFASs investigated, eight can inhibit at least one of four hCA isozymes (I, II, IX, and XII) with submicromolar inhibition constants, including perfluorooctanoic acid, perfluorooctanesulfonamide, and perfluorooctanesulfonic acid. Some PFASs, including those with both short and long perfluoromethylene chains, can effectively inhibit at least one hCA isozyme with low nanomolar inhibition constants.

Synthesis of some N-aroyl-2-oxindole benzenesulfonamide conjugates with carbonic anhydrase inhibitory activity

Implication of carbonic anhydrases (CAs) in many physiological functions made them attractive therapeutic targets. Herein, we report the synthesis of three series of benzenesulfonamide-based compounds (5a-e, 9a-e and 10a-e) as potential ligands to four of the human CA isoforms (hCA I, hCA II, hCA IX and hCA XII). All synthesized compounds were evaluated for their CA inhibitory activity. Most of the compounds preferentially inhibited the tumor-associated isoforms IX and XII. Series 9a-e and 10a-e showed the highest activity. Of particular interest was compound 10a which demonstrated the highest activity among all compounds with Ki of 68.3 and 21.5 nM against hCA IX and hCA XII, respectively, in addition to its highest selectivity index. To get deep insight on the interaction of compound 10a with CA, docking experiment was run to study the binding interaction with key amino acids and zinc ion in the catalytic site of the four isoforms studied.

7-Acylamino-3H-1,2-benzoxathiepine 2,2-dioxides as new isoform-selective carbonic anhydrase IX and XII inhibitors

A series of 3H-1,2-benzoxathiepine 2,2-dioxides incorporating 7-acylamino moieties were obtained by an original procedure starting from 5-nitrosalicylaldehyde, which was treated with propenylsulfonyl chloride followed by Wittig reaction of the bis-olefin intermediate. The new derivatives, belonging to the homosulfocoumarin chemotype, were assayed as inhibitors of the zinc metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1). Four pharmacologically relevant human (h) isoforms were investigated, the cytosolic hCA I and II and the transmembrane, tumour-associated hCA IX and XII. No relevant inhibition of hCA I and II was observed, whereas some of the new derivatives were effective, low nanomolar hCA IX/XII inhibitors, making them of interest for investigations in situations in which the activity of these isoforms is overexpressed, such as hypoxic tumours, arthritis or cerebral ischaemia.

Discovery of Potent Dual-Tailed Benzenesulfonamide Inhibitors of Human Carbonic Anhydrases Implicated in Glaucoma and in Vivo Profiling of Their Intraocular Pressure-Lowering Action

The design of three dual-tailed sulfonamide series 11a-11g, 14a-14h, and 16a-16e as carbonic anhydrase (CA, EC 4.2.1.1) inhibitors are presented. All compounds were evaluated for inhibitory action against pharmacologically relevant human CA isoforms I, II, IV, and VII. Compounds 11a-11g emerged as potent CA inhibitors against the four tested isoforms with a significant selectivity to CA II, which is implicated in glaucoma (K_i in the range 0.36-6.9 nM). X-ray crystallographic analysis of three compounds (11a, 11d, and 11g) bound to CA II showed the validity of the adopted drug design strategy as specific moieties within the ligand structure interacted directly with the hydrophobic and hydrophilic halves of the CA II active site. Compounds 11b-11d and 11g were evaluated for their intraocular pressure-lowering effects in a rabbit model of glaucoma. 11b and 11d showed significant efficacy when compared to the clinically used drug dorzolamide.

Sulfonamide-based ring-fused analogues for CAN508 as novel carbonic anhydrase inhibitors endowed with antitumor activity: Design, synthesis, and in vitro biological evaluation

In the present study, we report the design and synthesis of novel CAN508 sulfonamide-based analogues (4, 8a-e, 9a-h and 10a-e) as novel carbonic anhydrase (CA) inhibitors with potential CDK inhibitory activity. A bioisosteric replacement approach was adopted to replace the phenolic OH of CAN508 with a sulfamoyl group to afford compound 4. Thereafter, a ring-fusion approach was utilized to furnish the 5/5 fused imidazopyrazoles 8a-e which were subsequently expanded to 6/5 pyrazolopyrimidines 9a-h and 10a-e. All the synthesized analogues were evaluated for their inhibitory activity toward isoforms hCA I, II, IX and XII. The target tumor-associated isoforms hCA IX and XII were effectively inhibited with K_Is ranges 6-67.6 and 10.1-88.6 nM, respectively. Furthermore, all compounds were evaluated for their potential CDK2 and 9 inhibitory activities. Pyrazolopyrimidines 9d, 9e and 10b displayed weak CDK2 inhibitory activity (IC₅₀ = 6.4, 8.0 and 11.6 μM, respectively), along with abolished CDK9 inhibitory activity. This trend suggested that pyrazolopyrimidine derivatives merit further optimization to furnish more effective CDK2 inhibitor lead. On account of their excellent activity and selectivity towards hCA IX and XII, pyrazolopyrimidines 10 were evaluated for their anti-proliferative activity toward breast cancer MCF-7 and MDA-MB-468 cell lines under normoxic and hypoxic conditions. The most potent anti-proliferative agents 10a, 10c and 10d significantly increased cell percentage at sub-G1 and G2-M phases with concomitant decrease in the S phase population in MCF-7 treated cells. Finally, a docking study was undertaken to investigate the binding mode for the most selective hCA IX and XII inhibitors 10a-e, within hCA II, IX and XII active sites.

Synthesis and selective inhibitory effects of some 2-oxindole benzenesulfonamide conjugates on human carbonic anhydrase isoforms CA I, CA II, CA IX and CAXII

Three series of 2-oxindole benzenesulfonamide conjugates with different linkers were prepared by the condensation reaction of isatin derivatives 1a-e with different benzenesulfonamides. They were screened for their ability to inhibit human (h) carbonic anhydrase (CA, EC 4.2.1.1) isoforms hCA I, hCA II, hCA IX and hCA XII. Many compounds revealed promising activity and selectivity toward CAI, CAII and CAIX compared to acetazolamide (AAZ) especially compounds 2b (KI = 97.6, 8.0 nM against hCA I, hCA II, respectively) and 3a (KI = 90.2, 6.5 and 21.4 nM against hCA I, hCA II and hCA IX, respectively) relative to AAZ (KI = 250, 12 and 25 nM). Additionally, compound 4a revealed the highest activity against hCA II and hCA IX with KI of 3.0 and 13.9 nM, respectively. Docking of 2b, 3a and 4a into the active site of CA I, II, IX and XII revealed binding mode comparable to AAZ confirming the inhibition results.

Synthesis, biological and molecular dynamics investigations with a series of triazolopyrimidine/triazole-based benzenesulfonamides as novel carbonic anhydrase inhibitors

In the presented work, we report the design and synthesis of different new sets of triazolopyrimidine-based (9a-d) and triazole-based (11a-h, 13a-c, 15a,b, 17a,b and 21a-g) benzenesulfonamides. The newly synthesized sulfonamides were assessed for their inhibitory activities toward four human (h) metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1) isoforms; hCA I, II, IX and XII. The four examined isoforms were inhibited by the prepared sulfonamides (9a-d, 11a-h, 13a-c, 15a,b, 17a,b and 21a-g) in variable degrees with KIs ranges: 94.4-4953.5 nM for hCA I, 6.9-837.6 nM for hCA II, 3.3-85.0 nM for hCA XI, and 4.4-105.0 nM for hCA XII. In particular, sulfonamides 11e, 21a and 21e emerged as single-digit nanomolar hCA IX and hCA XII inhibitors. Interestingly, triazolopyrimidine-based sulfonamide 9d and triazole-based sulfonamide 21e were found to be the most selective hCA IX inhibitors over hCA I (SI = 100.85 and 210.58, respectively) and hCA II (SI = 18.54 and 38.36, respectively). Thereafter, sulfonamides 9d and 21e were docked into the active site of CAs II, IX and XII, then poses showing the best scoring values and favorable binding interactions were subjected to a MM-GBSA based refinement and, limited to CA IX and XII, to a cycle of 100 ns molecular dynamics.

Inhibition survey with phenolic compounds against the δ- and η-class carbonic anhydrases from the marine diatom thalassiosira weissflogii and protozoan Plasmodium falciparum

The inhibition of δ- and η-class carbonic anhydrases (CAs; EC 4.2.1.1) was poorly investigated so far. Only one δ-CA, TweCA from the diatom Thalassiosira weissflogii, and one η-CA, PfCA, from Plasmodium falciparum, have been cloned and characterised to date. To enrich δ- and η-CAs inhibition profiles, a panel of 22 phenols was investigated for TweCA and PfCA inhibition. Some derivatives showed effective, sub-micromolar inhibition of TweCA (K_Is 0.81–65.4 µM) and PfCA (K_Is 0.62–78.7 µM). A subset of compounds demonstrated a significant selectivity for the target CAs over the human physiologically relevant ones. This study promotes the identification of new potent and selective inhibitors of TweCA and PfCA, which could be considered as leads for finding molecular probes in the study of carbon fixation processes (in which TweCA and orthologue enzymes are involved) or drug candidates in the treatment of malaria.

3-Hydrazinoisatin-based benzenesulfonamides as novel carbonic anhydrase inhibitors endowed with anticancer activity: Synthesis, in vitro biological evaluation and in silico insights

Herein we describe the design and synthesis of two series of sulfonamides featuring N-unsubstituted (4a-c) or N-substituted (7a-o) isatin moieties (as tails) connected to benzenesulfonamide moiety via a hydrazine linker. All the prepared sulfonamides (4a-c and 7a-o) showed potent inhibitory activities toward transmembrane tumor-associated human (h) carbonic anhydrase (hCA, EC 4.2.1.1) isoforms, IX and XII with KI range (8.3-65.4 nM) and (11.9-72.9 nM), respectively. Furthermore, six sulfonamides (7e, 7i, 7j, 7m, 7n and 7o) were assessed for their anti-proliferative activity, according to US-NCI protocol, toward a panel of sixty cancer cell lines. Compounds 7j and 7n were the most promising counterparts in this assay displaying broad spectrum anti-proliferative activity toward diverse cell lines. Also, sulfonamide 7n significantly inhibited clonogenicity of HCT-116 cells in a concentration dependent manner in the colony forming assay. Moreover, molecular modeling studies were performed to gain insights for the plausible binding interactions and affinities for the target isatin-based sulfonamides (4a-c and 7a-o) within hCA isoforms II and IX active sites.

Continued exploration and tail approach synthesis of benzenesulfonamides containing triazole and dual triazole moieties as carbonic anhydrase I, II, IV and IX inhibitors

A library of twenty two novel 1,2,3-triazole benzenesulfonamides incorporating thiosemicarbazide, 5(4H)-thione-1,2,4-triazole and variously substituted phenacyl appended 1,2,4-triazole as tail were designed, synthesized and assessed for their efficacy as inhibitors against carbonic anhydrase human (h) isoforms hCA I, II, IV and IX. The physiologically important and off-target cytosolic isoform hCA I was weakly inhibited by most of the newly synthesized sulfonamides while the glaucoma associated isoform hCA II was moderately inhibited with KIs spanning in low nanomolar range (KI = 8.0 nM-0.903 μM). The membrane bound isoform hCA IV, which is known to be involved in glaucoma and retinitis pigmentosa among others, was strongly inhibited by all newly synthesized sulfonamides out of which nine compounds inhibited isoform hCA IV even more effectively as compared to standard drug acetazolamide (AAZ). The membrane bound isoform hCA IX, associated with growth of tumor cells, was moderately inhibited with KIs ranging between 51 nM-3.198 μM. The effect of appending variously substituted tails on heterocyclic moieties over inhibition potential of synthesized sulfonamides is also disclosed which can be of further interest in pharmacological studies for exploring synthesis of isoform selective inhibitors.

Exploring benzoxaborole derivatives as carbonic anhydrase inhibitors: a structural and computational analysis reveals their conformational variability as a tool to increase enzyme selectivity

Recent studies identified the benzoxaborole moiety as a new zinc-binding group able to interact with carbonic anhydrase (CA) active site. Here, we report a structural analysis of benzoxaboroles containing urea/thiourea groups, showing that these molecules are very versatile since they can bind the enzyme assuming different binding conformations and coordination geometries of the catalytic zinc ion. In addition, theoretical calculations of binding free energy were performed highlighting the key role of specific residues for protein-inhibitor recognition. Overall, these data are very useful for the development of new inhibitors with higher selectivity and efficacy for various CAs.

Bioisosteric Development of Multitarget Nonsteroidal Anti-Inflammatory Drug-Carbonic Anhydrases Inhibitor Hybrids for the Management of Rheumatoid Arthritis

Multitarget nonsteroidal anti-inflammatory drug (NSAID)-carbonic anhydrase inhibitor (CAI) agents for the management of rheumatoid arthritis are reported. The evidence of the plasma stability of the amide-linked hybrids previously reported prompted us to investigate their pain-relieving mechanism of action. A bioisosteric amide to ester substitution yielded a series of derivatives showing potent target CAs inhibition and to undergo cleavage in rat or human plasma depending on the NSAID portion. A selection of derivatives were assayed in vitro to indirectly evaluate their effect on COX-1 and COX-2. MD simulations demonstrated that the entire hybrids are also able to efficiently bind the COX active site. In a rat model of RA, the most promising derivative (5c) showed major antihyperalgesic action compared with the equimolar coadministration of the single agents. The gathered data provided new insights on the action mechanism of these multitarget compounds, which induce markedly improved pain relief compared with the parent NSAIDs.

Extending the Inhibition Profiles of Coumarin-Based Compounds Against Human Carbonic Anhydrases: Synthesis, Biological, and In Silico Evaluation

Carbonic anhydrases (CAs, EC 4.2.1.1) catalyze the fundamental reaction of CO₂ hydration in all living organisms and are actively involved in the regulation of a plethora of pathological and physiological conditions. A set of new coumarin/ dihydrocoumarin derivatives was here synthesized, characterized, and tested as human CA inhibitors. Their inhibitory activity was evaluated against the cytosolic human isoforms hCA I and II and the transmembrane hCA IX and hCA XII. Two compounds showed potent inhibitory activity against hCA IX, being more active or equipotent with the reference drug acetazolamide. Computational procedures were used to investigate the binding mode of this class of compounds within the active site of hCA IX and XII that are validated as anti-tumor targets.

Synthesis, biological evaluation and in silico studies with 4-benzylidene-2-phenyl-5(4H)-imidazolone-based benzenesulfonamides as novel selective carbonic anhydrase IX inhibitors endowed with anticancer activity

In the presented work, we report the synthesis of a series of 4-benzylidene-2-phenyl-5(4H)-imidazolone-based benzenesulfonamides 7a-fvia the Erlenmeyer-Plöchl reaction. All the prepared imidazolones 7a-f were evaluated as inhibitors of human (h) carbonic anhydrases (CA, EC 4.2.1.1) cytosolic isoforms hCA I and II, as well as transmembrane tumor-associated isoforms hCA IX and XII. All the tested hCA isoforms were inhibited by the prepared imidazolones 7a-f in variable degrees with the following KIs ranges: 673.2-8169 nM for hCA I, 61.2-592.1 nM for hCA II, 23-155.4 nM for hCA XI, and 21.8-179.6 nM for hCA XII. In particular, imidazolones 7a, 7e, and 7f exhibited good selectivity towards the tumor-associated isoforms (CAs IX and XII) over the off-target cytosolic (CAs I and II) with selectivity index (SI) in the range of 6.2-19.4 and 3.3-8, respectively. Moreover, imidazolones 7a-f were screened for their anticancer activity in one dose (10-5 M) assay against a panel of 60 cancer cell lines according to US-NCI protocol. Furthermore, 7a, 7e and 7f were evaluated for their anti-proliferative activity against colorectal cancer HCT-116 and breast cancer MCF-7 cell lines. Furthermore, 7e and 7f were screened for cell cycle disturbance and apoptosis induction in HCT-116 cells. Finally, a molecular docking study was carried out to rationalize the obtained results.

Carbonic anhydrase inhibitors based on sorafenib scaffold: Design, synthesis, crystallographic investigation and effects on primary breast cancer cells

Carbonic anhydrase inhibitors (CAIs) of the sulfonamide, sulfamate and coumarin classes bearing the phenylureido tail found in the clinically used drug Sorafenib, a multikinase inhibitor actually used for the management of hepatocellular carcinomas, are reported. All compounds were assayed on human (h) CA isoforms I, II, VII and IX, involved in various pathologies. Among the sulfonamides, several compounds were selective for inhibiting hCA IX, with K_I values in the low nanomolar ranges (i.e. 0.7-30.2 nM). We explored the binding modes of such compounds by means of X-ray crystallographic studies on isoform hCA I in adduct with one sulfonamide and a sulfamate inhibitor. Antiproliferative properties of some sulfamates on breast tumor cell lines were also investigated.

Application of hydrazino and hydrazido linkers to connect benzenesulfonamides with hydrophilic/phobic tails for targeting the middle region of human carbonic anhydrases active site: Selective inhibitors of hCA IX

Herein we report the design and synthesis of three different sets of novel benzenesulfonamides (5a-e, 7a-e and 10a-d) incorporating hydrophilic/hydrophobic tails by hydrazido or hydrazino linkers. The newly synthesized benzenesulfonamides were examined in vitro for their inhibitory activity towards four human (h) carbonic anhydrase (hCA, EC 4.2.1.1) isoforms, hCA I, II, IX and XII using a stopped-flow CO₂ hydrase assay. All these isoforms were inhibited by the sulfonamides (5a-e, 7a-e and 10a-d) with variable degrees in the following K_I ranges: 76.8-357.4 nM for hCA I, 8.2-94.6 nM for hCA II, 2.0-46.3 nM for hCA XI, and 8.3-88.3 nM for hCA XII. The sulfonamide 7d exhibited potent anti-proliferative activity against breast MCF-7 cancer cell line under both normoxic and hypoxic conditions with IC₅₀ values equal 3.32 ± 0.06 and 8.53 ± 0.32 μM, respectively, which are comparable to the reference drug doxorubicin (IC₅₀ = 2.36 ± 0.04 and 8.39 ± 0.25 μM, respectively). Furthermore, 7d was screened for cell cycle disturbance and apoptosis induction in MCF-7 cells. It was found to persuade cell cycle arrest at G2-M stage as well as to alter the Sub-G1 phase, also, 7d resulted in a significant increase in the percent of annexinV-FITC positive apoptotic cells from 1.03 to 18.54%. Molecular docking study was carried out for 7d within the hCA IX and hCA XII active sites to rationalize the obtained inhibition results.

Novel Diamide-Based Benzenesulfonamides as Selective Carbonic Anhydrase IX Inhibitors Endowed with Antitumor Activity: Synthesis, Biological Evaluation and In Silico Insights

In this work, we present the synthesis and biological evaluation of novel series of diamide-based benzenesulfonamides 5a–h as inhibitors of the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1) isoforms hCA I, II, IX and XII. The target tumor-associated isoforms hCA IX and XII were undeniably the most affected ones (K_Is: 8.3–123.3 and 9.8–134.5 nM, respectively). Notably, diamides 5a and 5h stood out as a single-digit nanomolar hCA IX inhibitors (K_Is = 8.8 and 8.3 nM). The SAR outcomes highlighted that bioisosteric replacement of the benzylidene moiety, compounds 5a–g, with the hetero 2-furylidene moiety, compound 5h, achieved the best IX/I and IX/II selectivity herein reported with SIs of 985 and 13.8, respectively. Molecular docking simulations of the prepared diamides within CA IX active site revealed the ability of 5h to establish an additional H-bond between the heterocyclic oxygen and HE/Gln67. Moreover, benzenesulfonamides 5a, 5b and 5h were evaluated for their antitumor activity against renal cancer UO-31 cell line. Compound 5h was the most potent derivative with about 1.5-fold more enhanced activity (IC₅₀ = 4.89 ± 0.22 μM) than the reference drug Staurosporine (IC₅₀ = 7.25 ± 0.43 μM). Moreover, 5a and 5h were able to induce apoptosis in UO-31 cells as evidenced by the significant increase in the percent of annexinV-FITC positive apoptotic cells by 22.5- and 26.5-folds, respectively.

Novel approaches for designing drugs that interfere with pH regulation

INTRODUCTION

In all living species, pH regulation is a tightly controlled process, with a plethora of proteins involved in its regulation. These include sodium-proton exchangers, carbonic anhydrases, anion exchangers, bicarbonate transporters/cotransporters, H⁺-ATPases, and monocarboxylate transporters. All of them play crucial roles in acid-base balancing, both in eukaryotic as well as in prokaryotic organisms, making them interesting drug targets for the management of pathological events (in)directly involved in pH regulation. Areas covered: Interfering with pH regulation for the treatment of tumors and microbial infections is the main focus of this review, with particular attention paid to inhibitors targeting the above-mentioned proteins. The latest advances in each field id reviewed. Expert opinion: Interfering with the pH regulation of tumor cells is a validated approach to tackle primary tumors and metastases growth. Carbonic anhydrases are the most investigated proteins of those aforementioned, with several inhibitors in clinical development. Recent advances in the characterization of proteins involved in pH homeostasis of various pathogens evidenced their crucial role in the survival and virulence of bacterial, fungal, and protozoan microorganisms. Some encouraging results shed light on the possibility to target such proteins for obtaining new anti-infectives, overcoming the extensive drug resistance problems of clinically used drugs.

4-Hydroxy-3-nitro-5-ureido-benzenesulfonamides Selectively Target the Tumor-Associated Carbonic Anhydrase Isoforms IX and XII Showing Hypoxia-Enhanced Antiproliferative Profiles

Human carbonic anhydrases (CA, EC, 4.2.1.1) IX and XII are overexpressed in cancer cells as adaptive response to hypoxia and acidic conditions characteristic of many tumors. In addition, hypoxia facilitates the activity of specific oxido-reductases that may be exploited to selectively activate bioreductive prodrugs. Here, new selective CA IX/XII inhibitors, as analogues of the antitumor phase II drug SLC-0111 are described, namely ureido-substituted benzenesulfonamides appended with a nitro-aromatic moiety to yield an antiproliferative action increased by hypoxia. These compounds were screened for the inhibition of the ubiquitous hCA I/II and the target hCA IX/XII. Six X-ray crystallographies with CA II and IX/mimic allowed for the rationalization of the compounds inhibitory activity. The effects of some such compounds on the viability of HT-29, MDA-MB-231, and PC-3 human cancer cell lines in both normoxic and hypoxic conditions were examined, providing the initiation toward the development of hypoxia-activated antitumor CAIs.

Enhancement of the tail hydrophobic interactions within the carbonic anhydrase IX active site via structural extension: Design and synthesis of novel N-substituted isatins-SLC-0111 hybrids as carbonic anhydrase inhibitors and antitumor agents

Herein we report the design and synthesis of novel N-substituted isatins-SLC-0111 hybrids (6a-f and 9a-l). A structural extension approach was adopted via N-alkylation and N-benzylation of isatin moiety to enhance the tail hydrophobic interactions within the carbonic anhydrase (CA) IX active site. Thereafter, a hybrid pharmacophore approach was utilized via merging the pharmacophoric elements of isatin and SLC-0111 in a single chemical framework. As planned, a substantial improvement of inhibitory profile of the target hybrids (K_Is: 4.7-86.1 nM) towards hCA IX in comparison to N-unsubstituted leads IVa-c (K_Is: 192-239 nM), was achieved. Molecular docking of the designed hybrids in CA IX active site unveiled, as planned, the ability of N-alkylated and N-benzylated isatin moieties to accommodate in a wide hydrophobic pocket formed by T73, P75, P76, L91, L123 and A128, establishing strong van der Waals interactions. Hybrid 6c displayed good anti-proliferative activity under hypoxic conditions towards breast cancer MDA-MB-231 and MCF-7 cell lines (IC₅₀ = 7.43 ± 0.28 and 12.90 ± 0.34 μM, respectively). Also, 6c disrupted the MDA-MB-231 cell cycle via alteration of the Sub-G₁ phase and arrest of G₂-M stage. Additionally, 6c displayed significant increase in the percent of annexinV-FITC positive apoptotic cells from 1.03 to 18.54%. Furthermore, 6c displayed potent VEGFR-2 inhibitory activity (IC₅₀ = 260.64 nM). Collectively, these data suggest 6c as a promising lead molecule for the development of effective anticancer agents.

Interaction of a gold(i) dicarbene anticancer drug with human telomeric DNA G-quadruplex: solution and computationally aided X-ray diffraction analysis

Solution and solid-state data give a quite clear picture for a bis carbene gold(i) complex having perspective anticancer properties.