Novel thiazolotriazole and triazolothiadiazine scaffolds as selective tumor associated carbonic anhydrase inhibitors endowed with cathepsin B inhibition

The present research focused on the tail-approach synthesis of novel extended thiazolotriazoles (8a-8j) and triazolothiadiazines (11a-11j) including aminotriazole intermediate 10. After successful synthesis, all the compounds were evaluated for their inhibition potential against cytosolic isoforms of human carbonic anhydrase (hCA I, II), tumor-linked transmembrane isoforms (hCA IX, XII), and cathepsin B. As per the inhibition data, the newly synthesized compounds showed poor inhibition against hCA I. Many of the compounds showed effective inhibition toward hCA IX and/or XII in low nanomolar concentration. Despite the strong to moderate inhibition of hCA II by these compounds, more than half of them demonstrated better inhibition against hCA IX and/or XII, comparatively. Further, insights of CA inhibition data of these extended analogs and their comparison with earlier reported thiazolotriazole and triazolothiadiazine derivatives might help in the rational design of novel potent and selective hCA IX and XII inhibitors. The novel compounds were also found to possess anti-cathepsin B potential at a low concentration of 10-7 M. Broadly, compounds of series 11a-11j presented more effective inhibition against cathepsin B than their counterparts in series 8a-8j. Moreover, these in vitro results with respect to cathepsin B inhibition were also supported by the in silico insights obtained via molecular modeling studies.

Keto-bridged dual triazole-linked benzenesulfonamides as potent carbonic anhydrase and cathepsin B inhibitors

Background: Inhibition of human carbonic anhydrase (hCA) isoforms IX and XII with concurrent inhibition of cathepsin B is a promising approach for targeting cancers. Methods/results: 28 keto-bridged dual triazole-containing benzenesulfonamides were synthesized and tested, following the multitarget approach, for their efficacy as inhibitors of cathepsin B and hCA isoforms (I, II, IX, XII). The synthesized compounds showed excellent inhibition of CA isoforms (IX and XII) and cathepsin B. Compound 8i exhibited better and more selective inhibition of the cancer-associated isoform hCA IX as compared with acetazolamide (reference drug) and SLC-0111 (potent lead as carbonic anhydrase inhibitor). Molecular docking studies were also carried out. Conclusion: The present work gives important generalizations for the development of isoform-selective hCA inhibitors endowed with anti-cathepsin properties.

Tail approach synthesis of triazolylthiazolotriazole bearing benzenesulfonamides as carbonic anhydrase inhibitors capable of inducing apoptosis

Inhibition of human carbonic anhydrase (hCA) isoform IX with concurrent induction of apoptosis is a promising approach for targeting cancer in humans. Prompted by the scope, novel benzenesulfonamides containing the 1,2,3-triazolylthiazolotriazole tail were synthesized and screened as inhibitors of hCA isoforms I, II, IV, and IX. The tumor-associated isoform hCA IX was strongly inhibited by the sulfonamides reported here with K_I values ranging from 45 nM to 1.882 μM. Overall, nine compounds showed hCA IX inhibition with K_I  < 250 nM. The glaucoma-associated isoform hCA II was moderately inhibited while the cytosolic isoform hCA I and membrane-bound isoform hCA IV were weakly inhibited by the synthesized sulfonamides. Compound 6Ac (K_I  = 3.6 nM) was found to be an almost three times more potent inhibitor of hCA II as compared to the standard drug acetazolamide (K_I  = 12.1 nM). The selective hCA IX inhibitors were further studied for their apoptotic efficacy in goat ovarian cells and showed better results as compared to the control. A comparative study of previously synthesized compounds and molecular docking study of representative compounds revealed some important generalizations that could prove beneficial in further investigations of isoform-selective hCA inhibitors.

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.

Stereocontrolled Synthesis of the Fully Glycosylated Monomeric Unit of Lomaiviticin A

We describe a stereocontrolled synthesis of 3, the fully glycosylated monomeric unit of the dimeric cytotoxic bacterial metabolite (-)-lomaiviticin A (2). A novel strategy involving convergent, site- and stereoselective coupling of the β,γ-unsaturated ketone 6 and the naphthyl bromide 7 (92%, 15:1 diastereomeric ratio (dr)), followed by radical-based annulation and silyl ether cleavage, provided the tetracycle 5 (57% overall), which contains the carbon skeleton of the aglycon of 3. The β-linked 2,4,6-trideoxy-4-aminoglycoside l-pyrrolosamine was installed in 73% yield and with 15:1 β:α selectivity using a modified Koenigs-Knorr glycosylation. The diazo substituent was introduced via direct diazo transfer to an electron-rich benzoindene (4 → 27). The α-linked 2,6-dideoxyglycoside l-oleandrose was introduced by gold-catalyzed activation of an o-alkynyl glycosylbenzoate (75%, >20:1 α:β selectivity). A carefully orchestrated endgame sequence then provided efficient access to 3. Cell viability studies indicated that monomer 3 is not cytotoxic at concentrations up to 1 μM, providing conclusive evidence that the dimeric structure of (-)-lomaiviticin A (2) is required for cytotoxic effects. The preparation of 3 provides a foundation to complete the synthesis of (-)-lomaiviticin A (2) itself.

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.

Olefination with Sulfonyl Halides and Esters: Synthesis of Unsaturated Sulfonyl Fluorides

Methanedisulfonyl fluoride, CH2(SO2F)2, transforms aromatic aldehydes into β-arylethenesulfonyl fluorides, useful substrates for the SuFEx "click"-type transformations. The reaction mimics mechanism of the Horner-Wadsworth-Emmons olefination, which runs via addition of the carbanion, followed by cyclization-fragmentation of the four-membered ring intermediate. In the absence of base, electron-rich aldehydes follow an alternative pathway of the Knoevenagel condensation to provide unsaturated 1,1-disulfonyl fluorides. We demonstrate also trapping of elusive ethene-1,1-disulfonyl fluoride, CH2═C(SO2F)2, with 4-(dimethylamino)pyridine (DMAP) that forms zwitterionic adduct, characterized with X-ray studies.

Pharmacological report of recently designed multifunctional coumarin and coumarin-heterocycle derivatives

Coumarin is a naturally available molecule and has been identified as a potent pharmacophore due to its pharmacological activity. Because of this, coumarin has been exploited synthetically to prepare a wide range of derivatives. In fact, most coumarin derivatives have been found to be less toxic, which is the most essential property for a drug molecule. Such molecules are being prepared for therapeutic use as broad-spectrum pharmacological agents. Microbial diseases including viral diseases have become very common and are responsible for many deaths worldwide. In particular, microbial drug resistance is a problem that needs to be tackled in an effective manner. Also, for Alzheimer's disease, which affects most elderly persons, no efficient chemotherapy exists. In addition, although diabetes, a metabolic syndrome, can be treated with many drugs, there is no complete cure. Thus, more potent antidiabetic agents are required for the management of diabetes. Likewise, for the treatment of a wide range of ailments caused by microbes, genetic factors, or lifestyle-related factors, an efficient drug regimen is needed. In view of this, coumarin derivatives are designed and evaluated. Here, coumarin derivatives that have been reported recently are compiled, classified and evaluated critically. This study briefly takes the structure-activity relationship into consideration and suggests the next suitable step. With a focus on the most potent molecules, the pharmacological activity of the evaluated molecules is described.

Tail approach synthesis of novel benzenesulfonamides incorporating 1,3,4-oxadiazole hybrids as potent inhibitor of carbonic anhydrase I, II, IX, and XII isoenzymes

Two new series of 1,3,4-oxadiazole benzenesulfonamide hybrids 3 and 4, having twenty novel compounds, have been designed and synthesized in order to assess their inhibition potential as CAIs against hCA I, II, IX, and XII. 'Tail approach' strategy has been used to design the aromatic sulfonamide scaffolds with carbonyl and amide linker. Excellent inhibitory activity against hCA I has been exhibited by compounds 3g and 4j, 3.5 magnitude of order better than reference drug AAZ (KI = 250 nM). Moreover, compound 4j (KI = 7.9 nM) effectively inhibited glaucoma-associated hCA II isoform as well as tumor-associated hCA IX isoform with KI = 16.3 nM. Further hCA XII was weakly inhibited by all the compounds with KI values ranging from 0.23 μM to 3.62 μM. Interestingly structure-activity relationship (SAR) study indicates that N-(3-nitrophenyl)-2-((5-(4-sulfamoylphenyl)-1,3,4-oxadiazol-2-yl)thio)acetamide (4j) is a potent compound to be investigated further for antiglaucoma and antitumor activity. The chemistry of the nature of different substitutions on the 1,3,4-oxadiazole bearing benzenesulfonamide substituted aromatic ring for potency and selectivity over one hCA isoform versus others is deliberated in the present study. In this context, the 1,3,4-oxadiazole motif can be a valuable tool worth developing for the procurement of novel and potent selective CAIs potentially useful for the management of a variety of diseases as chemotherapeutic agents.

Photosensitive nanocarriers for specific delivery of cargo into cells

Nanoencapsulation is a rapidly expanding technology to enclose cargo into inert material at the nanoscale size, which protects cargo from degradation, improves bioavailability and allows for controlled release. Encapsulation of drugs into functional nanocarriers enhances their specificity, targeting ability, efficiency, and effectiveness. Functionality may come from cell targeting biomolecules that direct nanocarriers to a specific cell or tissue. Delivery is usually mediated by diffusion and erosion mechanisms, but in some cases, this is not sufficient to reach the expected therapeutic effects. This work reports on the development of a new photoresponsive polymeric nanocarrier (PNc)-based nanobioconjugate (NBc) for specific photo-delivery of cargo into target cells. We readily synthesized the PNcs by modification of chitosan with ultraviolet (UV)-photosensitive azobenzene molecules, with Nile red and dofetilide as cargo models to prove the encapsulation/release concept. The PNcs were further functionalized with the cardiac targeting transmembrane peptide and efficiently internalized into cardiomyocytes, as a cell line model. Intracellular cargo-release was dramatically accelerated upon a very short UV-light irradiation time. Delivering cargo in a time-space controlled fashion by means of NBcs is a promising strategy to increase the intracellular cargo concentration, to decrease dose and cargo side effects, thereby improving the effectiveness of a therapeutic regime.

Azopolymer based nanoparticles for phototriggered drug delivery

Controlled release by stimulus-responsive nanoparticles is oriented to increase the specificity of drug delivery, to improve the therapy effectiveness and minimizing side effects. This work presents the synthesis of photosensitive-polymeric nanoparticles as a potential system for localized drug delivery. First, the photoisomerizable amphiphilic-copolymer poly2-[4-phenylazophenoxy]ethyl acrylate-co-acrylic acid (PPAPE), was synthesized. Then, PPAPE was employed to prepare micellar nanoparticles by the nanoprecipitation method. Characterizations of the polymer were performed by proton nuclear magnetic resonance, X-ray photoelectron spectroscopy and FTIR spectroscopy. The morphology of the nanoparticles was analyzed by dynamic light scattering and transmission electron microscopy. Also, photostimulation response was confirmed by UV-VIS spectroscopy. Results indicate that the obtained photoresponsive nanoparticles have the size and photoisomerization necessary to perform the specific release of drugs.

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.

State of the Art on Carbonic Anhydrase Modulators for Biomedical Purposes

The current review is intended to highlight recent advances in the search of new and effective modulators of the metalloenzymes Carbonic Anhydrases (CAs, EC 4.2.1.1) expressed in humans (h). CAs reversibly catalyze the CO2 hydration reaction, which is of crucial importance in the regulation of a plethora of fundamental processes at cellular level as well as in complex organisms. The first section of this review will be dedicated to compounds acting as activators of the hCAs (CAAs) and their promising effects on central nervous system affecting pathologies mainly characterized from memory and learning impairments. The second part will focus on the emerging chemical classes acting as hCA inhibitors (CAIs) and their potential use for the treatment of diseases.

Progress in the synthesis of δ-sultones

Abstract

Sultones, the cyclic esters of hydroxyl sulfonic acids, are a fascinating class of heterocycles and the recent years have witnessed an increasing interest in these molecules, especially in six-ring δ-sultones. The importance of these compounds is either because of their biological properties themselves or due to their versatility as intermediates in more complex target syntheses. Accordingly, the development of new synthesis methods to access δ-sultones is an important and rewarding task which we wish to highlight in this review.

Graphical abstract

Inhibition of carbonic anhydrase IX targets primary tumors, metastases, and cancer stem cells: Three for the price of one

Human carbonic anhydrase (CA) IX is a tumor-associated protein, since it is scarcely present in normal tissues, but highly overexpressed in a large number of solid tumors, where it actively contributes to survival and metastatic spread of tumor cells. Due to these features, the characterization of its biochemical, structural, and functional features for drug design purposes has been extensively carried out, with consequent development of several highly selective small molecule inhibitors and monoclonal antibodies to be used for different purposes. Aim of this review is to provide a comprehensive state-of-the-art of studies performed on this enzyme, regarding structural, functional, and biomedical aspects, as well as the development of molecules with diagnostic and therapeutic applications for cancer treatment. A brief description of additional pharmacologic applications for CA IX inhibition in other diseases, such as arthritis and ischemia, is also provided.

Synthesis of novel 5-amino-1,3,4-thiadiazole-2-sulfonamide containing acridine sulfonamide/carboxamide compounds and investigation of their inhibition effects on human carbonic anhydrase I, II, IV and VII

Herein, we report that acridine intermediates 5 were obtained from the reduction of nitro acridine derivatives 4, which were synthesized via condensation of dimedone, p-nitrobenzaldehyde with 4-amino-N-(5-sulfamoyl-1,3,4-thiadiazol-2-yl)benzamide, respectively. Then acridine sulfonamide/carboxamide (7a-i) compounds were synthesized by reaction of amino acridine 5 with sulfonyl chlorides and carbamoyl chlorides. The new compounds were characterized by melting points, FT-IR, ¹H NMR, ¹³C NMR and HRMS analyzes. The evaluation of in vitro test of the synthesized compounds against hCA I, II, IV and VII showed that some of them are potent inhibitors. Among them, compound 7e showed the most potent activity against hCA II with a K_I of 7.9 nM.

Protonography and anion inhibition profile of the α-carbonic anhydrase (CruCA4) identified in the Mediterranean red coral Corallium rubrum

CruCA4 is a secreted isoform of the α-carbonic anhydrase (CA, EC 4.2.1.1) family, which has been identified in the octocoral Corallium rubrum. This enzyme is involved in the calcification process leading to the formation of the coral calcium carbonate skeleton. We report here experiments performed on the recombinant CruCA4 with the technique of protonography that can be used to detect in a simple way the enzyme activity. We have also investigated the inhibition profile of CruCA4 with one major class of CA inhibitors, the inorganic anions. A range of weak and moderate inhibitors have been identified having K_I in the range of 1-100 mM, among which the halides, pseudohalides, bicarbonate, sulfate, nitrate, nitrite, and many complex inorganic anions. Stronger inhibitors were sulfamide, sulfamate, phenylboronic acid, phenylarsonic acid, and diethylditiocarbamate, which showed a better affinity for this enzyme, with K_I in the range of 75 μM-0.60 mM. All these anions/small molecules probably coordinate to the Zn(II) ion within the CA active site as enzyme inhibition mechanism.

Sequence Analysis, Kinetic Constants, and Anion Inhibition Profile of the Nacrein-Like Protein (CgiNAP2X1) from the Pacific Oyster Magallana gigas (Ex-Crassostrea gigas)

The carbonic anhydrase (CA, EC 4.2.1.1) superfamily of metalloenzymes catalyzes the hydration of carbon dioxide to bicarbonate and protons. The catalytically active form of these enzymes incorporates a metal hydroxide derivative, the formation of which is the rate-determining step of catalytic reaction, being affected by the transfer of a proton from a metal-coordinated water molecule to the environment. Here, we report the cloning, expression, and purification of a particular CA, i.e., nacrein-like protein encoded in the genome of the Pacific oyster Magallana gigas (previously known as Crassostrea gigas). Furthermore, the amino acid sequence, kinetic constants, and anion inhibition profile of the recombinant enzyme were investigated for the first time. The new protein, CgiNAP2X1, is highly effective as catalyst for the CO₂ hydration reaction, based on the measured kinetic parameters, i.e., k_cat = 1.0 × 10⁶ s⁻¹ and k_cat/K_M = 1.2 × 10⁸ M⁻¹·s⁻¹. CgiNAP2X1 has a putative signal peptide, which probably allows an extracellular localization of the protein. The inhibition data demonstrated that the best anion inhibitors of CgiNAP2X1 were diethyldithiocarbamate, sulfamide, sulfamate, phenylboronic acid and phenylarsonic acid, which showed a micromolar affinity for this enzyme, with K_Is in the range of 76–87 μM. These studies may add new information on the physiological role of the molluskan CAs in the biocalcification processes.

Advances in structure-based drug discovery of carbonic anhydrase inhibitors

INTRODUCTION

The enzyme carbonic anhydrase (CA, EC 4.2.1.1) is found in numerous organisms across the tree of life, with seven distinct classes known to date. CA inhibition can be exploited for the treatment of edema, glaucoma, seizures, obesity, cancer and infectious diseases. A myriad of CA inhibitor (CAI) classes and inhibition mechanisms have been identified over the past decade, mainly through structure-based drug design approaches. Five different CA inhibition mechanisms are presently known. Areas covered: Recent advances in structure-based CAI design are reviewed, with periodic table-based organization of inhibitor classes. Expert opinion: Various structure-based drug design studies have led to deep understanding of factors governing tight binding and selectivity for the various isoforms. Carboxylic acids, phenols, polyamines, diols, borols, boronic acids, coumarins and sulfonamides represent successful stories which led to an anti-tumor sulfonamide in Phase I clinical trials (SLC-0111). For many inhibitor classes, no detailed crystallographic data are available. Detailed structural characterization of all CAI classes may lead to further advances in the field with potential therapeutic implications in the management of indications including neuropathic pain, cerebral ischemia, arthritis and tumor imaging.

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

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

How many carbonic anhydrase inhibition mechanisms exist?

Six genetic families of the enzyme carbonic anhydrase (CA, EC 4.2.1.1) were described to date. Inhibition of CAs has pharmacologic applications in the field of antiglaucoma, anticonvulsant, anticancer, and anti-infective agents. New classes of CA inhibitors (CAIs) were described in the last decade with enzyme inhibition mechanisms differing considerably from the classical inhibitors of the sulfonamide or anion type. Five different CA inhibition mechanisms are known: (i) the zinc binders coordinate to the catalytically crucial Zn(II) ion from the enzyme active site, with the metal in tetrahedral or trigonal bipyramidal geometries. Sulfonamides and their isosters, most anions, dithiocarbamates and their isosters, carboxylates, and hydroxamates bind in this way; (ii) inhibitors that anchor to the zinc-coordinated water molecule/hydroxide ion (phenols, carboxylates, polyamines, 2-thioxocoumarins, sulfocoumarins); (iii) inhibitors which occlude the entrance to the active site cavity (coumarins and their isosters), this binding site coinciding with that where CA activators bind; (iv) compounds which bind out of the active site cavity (a carboxylic acid derivative was seen to inhibit CA in this manner), and (v) compounds for which the inhibition mechanism is not known, among which the secondary/tertiary sulfonamides as well as imatinib/nilotinib are the most investigated examples. As CAIs are used clinically in many pathologies, with a sulfonamide inhibitor (SLC-0111) in Phase I clinical trials for the management of metastatic solid tumors, this review updates the recent findings in the field which may be useful for a structure-based drug design approach of more selective/potent modulators of the activity of these enzymes.