Carbonic anhydrase inhibitors: The membrane-associated isoform XV is highly inhibited by inorganic anions

The membrane-associated mouse isozyme of carbonic anhydrase XV (mCA XV), has been investigated for its interaction with anion inhibitors. mCA XV is an isoforms possessing a very particular inhibition profile by anions, dissimilar to that of all other mammalian CAs investigated earlier. Many simple inorganic anions (thiocyanate, cyanide, azide, bicarbonate, hydrogen sulfide, bisulfite and sulfate) showed low micromolar inhibition constants against mCA XV (K_Is of 8.2–10.1 μM), whereas they acted as much weaker (usually millimolar) inhibitors of other isoforms. Halides, nitrate, nitrite, carbonate, sulfamate, sulfamide and phenylboronic/arsonic acid were weaker inhibitors, with inhibition constants in the range of 27.6–288 μM. Our data may be useful for the design of more potent inhibitors of mCA XV (considering various zinc binding groups present in the anions investigated here, e.g., the sulfonate one) and for understanding some physiologic/pharmacologic consequences of mCA XV inhibition by anions such as bicarbonate or sulfate which show quite high affinity for it.     

Carbonic anhydrase inhibitors. The nematode α-carbonic anhydrase of Caenorhabditis elegans CAH-4b is highly inhibited by 2-(hydrazinocarbonyl)-3-substituted-phenyl-1H-indole-5-sulfonamides

A series of 2-(hydrazinocarbonyl)-3-substituted-phenyl-1H-indole-5-sulfonamides possessing various 2-, 3- or 4-substituted phenyl groups with methyl-, halogeno- and methoxy-functionalities, as well as the perfluorophenyl moiety, have been evaluated as inhibitors of an α-carbonic anhydrase (CA, EC 4.2.1.1) of the nematode model organism Caenorhabditis elegans (CAH-4b, or ceCA). The substitution pattern at the 3-phenyl ring highly influenced the ceCA inhibitory activity of these heterocyclic sulfonamides, with best inhibitors (K_Is in the range of 6.0–13.4 nM) incorporating 3-methyl-, 4-methyl-, 2-/3-/4-fluoro-, 4-chloro- and 3-/4-bromo-phenyl such moieties. Some of these sulfonamides also showed a good selectivity profile for the inhibition of the nematode over the human isozymes CA I and II (selectivity ratios in the range of 1.78–4.95 for the inhibition of ceCA over hCA II). These data can be used for the design of possibly new antihelmintic drugs, since the genome of many parasitic nematodes encode for a multitude of orthologue CA isozymes to ceCA investigated here.     

Carbonic anhydrase inhibitors. Inhibition of the β-class enzymes from the fungal pathogens Candida albicans and Cryptococcus neoformans with aliphatic and aromatic carboxylates

The inhibition of the β-carbonic anhydrases (CAs, EC 4.2.1.1) from the pathogenic fungi Cryptococcus neoformans (Can2) and Candida albicans (Nce103) with carboxylates such as the C1–C5 aliphatic carboxylates, oxalate, malonate, maleate, malate, pyruvate, lactate, citrate and some benzoates has been investigated. The best Can2 inhibitors were acetate and maleate (K_Is of 7.3–8.7 μM), whereas formate, acetate, valerate, oxalate, maleate, citrate and 2,3,5,6-tetrafluorobenzoate showed less effective inhibition, with K_Is in the range of 42.8–88.6 μM. Propionate, butyrate, malonate, l-malate, pyruvate, l-lactate and benzoate, were weak Can2 inhibitors, with inhibition constants in the range of 225–1267 μM. Nce103 was more susceptible to inhibition with carboxylates compared to Can2, with the best inhibitors (maleate, benzoate, butyrate and malonate) showing K_Is in the range of 8.6–26.9 μM. l-Malate and pyruvate together with valerate were the less efficient Nce103 inhibitors (K_Is of 87.7–94.0 μM), while the remaining carboxylates showed a compact behavior of efficient inhibitors (K_Is in the range of 35.1–61.6 μM). Notably the inhibition profiles of the two fungal β-CAs was very different from that of the ubiquitous host enzyme hCA II (belonging to the α-CA family), with maleate showing selectivity ratios of 113.6 and 115 for Can2 and Nce103, respectively, over hCA II inhibition. Therefore, maleate is a promising starting lead molecule for the development of better, low nanomolar, selective β-CA inhibitors.     

Carbonic anhydrase inhibitors: Valdecoxib binds to a different active site region of the human isoform II as compared to the structurally related cyclooxygenase II "selective" inhibitor celecoxib

The high resolution X-ray crystal structure of the adduct of human carbonic anhydrase (CA, EC 4.2.1.1) isoform II (hCA II) with the clinically used painkiller valdecoxib, acting as a potent CA II and cyclooxygenase-2 (COX-2) inhibitor, is reported. The ionized sulfonamide moiety of valdecoxib is coordinated to the catalytic Zn(II) ion with a tetrahedral geometry. The phenyl-isoxazole moiety of the inhibitor fills the active site channel and interacts with the side chains of Gln92, Val121, Leu198, Thr200, and Pro202. Its 3-phenyl group is located into a hydrophobic pocket, simultaneously establishing van der Waals interactions with the aliphatic side chain of various hydrophobic residues (Val135, Ile91, Val121, Leu198, and Leu141) and a strong offset face-to-face stacking interaction with the aromatic ring of Phe131 (the chi1 angle of which is rotated about 90 degrees with respect to what was observed in the structure of the native enzyme and those of other sulfonamide complexes). Celecoxib, a structurally related COX-2 inhibitor for which the X-ray crystal structure was reported earlier, binds in a completely different manner to hCA II as compared to valdecoxib. Celecoxib completely fills the entire CA II active site, with its trifluoromethyl group in the hydrophobic part of the active site and the p-tolyl moiety in the hydrophilic one, not establishing any interaction with Phe131. In contrast to celecoxib, valdecoxib was rotated about 90 degrees around the chemical bond connecting the benzensulfonamide and the substituted isoxazole ring allowing for these multiple favorable interactions. These different binding modes allow for the further drug design of various CA inhibitors belonging to the benzenesulfonamide class.     

3D QSAR studies,pharmacophore modeling,and virtual screening of diarylpyrazole–benzenesulfonamide derivatives as a template to obtain new inhibitors,using human carbonic anhydrase II as a model protein

A 3D-QSAR modeling was performed on a series of diarylpyrazole-benzenesulfonamide derivatives acting as inhibitors of the metalloenzyme carbonic anhydrase (CA, EC 4.2.1.1). The compounds were collected from two datasets with the same scaffold, and utilized as a template for a new pharmacophore model to screen the ZINC database of commercially available derivatives. The datasets were divided into training, test, and validation sets. As the first step, comparative molecular field analysis (CoMFA), CoMFA region focusing and comparative molecular similarity indices analysis (CoMSIA) in parallel with docking studies were applied to a set of 41 human (h) CA II inhibitors. The validity and the prediction capacity of the resulting models were evaluated by leave-one-out (LOO) cross-validation approach. The reliability of the model for the prediction of possibly new CA inhibitors was also tested.     

Synthesis,carbonic anhydrase I and II inhibition studies of the 1,3,5-trisubstituted-pyrazolines

4-(3-(4-Substituted-phenyl)-5-phenyl-4,5-dihydro-1H-pyrazol-1-yl) benzenesulfonamides (9–16) were successfully synthesized and their chemical structures were confirmed by ¹H NMR, ¹³C NMR, and HRMS spectra. Carbonic anhydrase I and II inhibitory effects of the compounds were investigated. K_i values of the compounds were in the range of 316.7?±?9.6–533.1?±?187.8?nM towards hCA I and 412.5?±?115.4–624.6?±?168.2?nM towards hCA II isoenzymes. While K_i values of the reference compound Acetazolamide were 278.8?±?44.3?nM and 293.4?±?46.4?nM towards hCA I and hCA II izoenzymes, respectively. Compound 14 with bromine and compound 13 with fluorine substituents can be considered as the leader compounds of the series because of the lowest K_i values in series to make further detailed carbonic anhydrase inhibiton studies.     

Carbonic anhydrase inhibitors: inhibition of cytosolic isozymes I and II with sulfamide derivatives

A novel class of effective CAIs has been identified, starting from a very weak carbonic anhydrase inhibitor (CAI), sulfamide, whose X-ray crystal structure in the adduct with hCA II has recently been reported. A series of N,N-disubstituted- and N-substituted-sulfamides were prepared from the corresponding amines and N-(tert-butoxycarbonyl)-N-[4-(dimethylazaniumylidene)-1,4-dihydropyridin-1-ylsulfonyl]azanide or the unstable N-(tert-butoxycarbonyl)sulfamoyl chloride. The disubstituted compounds being too bulky, were ineffective as CAIs, whereas mono-substituted derivatives (incorporating aliphatic, cyclic and aromatic moieties) as well as a bis-sulfamide, behaved as micro-nanomolar inhibitors of two cytosolic isozymes, hCA I and hCA II, responsible for critical physiological processes in higher vertebrates. Aryl-sulfamides were more effective than aliphatic derivatives. Low nanomolar inhibitors have been detected, which generally incorporated 4-substituted phenyl moieties in their molecule. This is the first example of CAIs in which low nanomolar inhibitors were generated starting from a very ineffective lead molecule.     

Carbonic anhydrase inhibitors. Preparation of potent sulfonamides inhibitors incorporating bile acid tails

Reaction of TBDMS-protected bile acids (cholic, chenodeoxycholic, deoxycholic, lithocholic, ursodeoxycholic acids) or dehydrocholic acid with aromatic/heterocyclic sulfonamides possessing free amino/hydroxy moieties, in the presence of carbodiimides, afforded after deprotection of the OTBDMS ethers, a series of sulfonamides incorporating bile acid moieties in their molecules. Many such derivatives showed strong inhibitory properties against three isozymes of carbonic anhydrase (CA, EC 4.2.1.1), that is CA I, II and IV, zinc enzymes playing critical roles in many pathologies, and which represent interesting targets for developing diverse pharmacological agents. Some of the most active derivatives, incorporating 1,3,4-thiadiazole-2-sulfonamide or benzothiazole-2-sulfonamide functionalities in their molecules, showed low nanomolar affinity for CA II and CAIV. Furthermore, the bioavailability of these derivatives in rabbits is comparable to that of acetazolamide, being in the range of 85-90%, showing them as promising candidates for systemically acting CA inhibitors.     

Anion inhibition studies of a beta carbonic anhydrase from the malaria mosquito Anopheles gambiae

An anion inhibition study of the β-class carbonic anhydrase, AgaCA, from the malaria mosquito Anopheles gambiae is reported. A series of simple as well as complex inorganic anions, and small molecules known to interact with CAs were included in the study. Bromide, iodide, bisulphite, perchlorate, perrhenate, perruthenate, and peroxydisulphate were ineffective AgaCA inhibitors, with K_Is?>?200?mM. Fluoride, chloride, cyanate, thiocyanate, cyanide, bicarbonate, carbonate, nitrite, nitrate, sulphate, stannate, selenate, tellurate, diphosphate, divanadate, tetraborate, selenocyanide, and trithiocarbonate showed K_Is in the range of 1.80–9.46?mM, whereas N,N-diethyldithiocarbamate was a submillimolar AgaCA inhibitor (K_I of 0.65?mM). The most effective AgaCA inhibitors were sulphamide, sulphamic acid, phenylboronic acid and phenylarsonic acid, with inhibition constants in the range of 21–84?µM. The control of insect vectors responsible of the transmission of many protozoan diseases is rather difficult nowadays, and finding agents which can interfere with these processes, as the enzyme inhibitors investigated here, may arrest the spread of these diseases worldwide.     

Terrigenous sediment-dominated reef platform infilling: an unexpected precursor to reef island formation and a test of the reef platform size–island age model in the Pacific

Low-lying coral reef islands are considered highly vulnerable to climate change, necessitating an improved understanding of when and why they form, and how the timing of formation varies within and among regions. Several testable models have been proposed that explain inter-regional variability as a function of sea-level history and, more recently, a reef platform size model has been proposed from the Maldives (central Indian Ocean) to explain intra-regional (intra-atoll) variability. Here we present chronostratigraphic data from Pipon Island, northern Great Barrier Reef (GBR), enabling us to test the applicability of existing regional island evolution models, and the platform size control hypothesis in a Pacific context. We show that reef platform infilling occurred rapidly (~4–5 mm yr⁻¹) under a “bucket-fill” type scenario. Unusually, this infilling was dominated by terrigenous sedimentation, with platform filling and subsequent reef flat formation complete by ~5000 calibrated years BP (cal BP). Reef flat exposure as sea levels slowly fell post highstand facilitated a shift towards intertidal and subaerial-dominated sedimentation. Our data suggest, however, a lag of ~1500 yr before island initiation (at ~3200 cal BP), i.e. later than that reported from smaller and more evolutionarily mature reef platforms in the region. Our data thus support: (1) the hypothesis that platform size acts to influence the timing of platform filling and subsequent island development at intra-regional scales; and (2) the hypothesis that the low wooded islands of the northern GBR conform to a model of island formation above an elevated reef flat under falling sea levels.