Oktay Talaz

α-Carbonic anhydrases are sulfatases with cyclic diol monosulfate esters

Carbonic anhydrases (CA) catalyze activated ester hydrolysis in addition to the hydration of CO2 to bicarbonate. They also show phosphatase activity with 4-nitrophenyl phosphate as substrate but not sulfatase with the corresponding sulfate. Here we prove that the enzyme is catalyzing the synthesis of cyclic diols from sulfate esters. 5-, 6- and 8-membered ring cyclic sulfates incorporating a neighboring secondary alcohol moiety were treated with CA II and yielded the corresponding cyclic diols. Inhibitory properties of obtained cyclic and original sulfate esters were then investigated on human carbonic anhydrase I (hCA I), hCA II, hCA IV and hCA VI (h = human isoform). KI-s of these compounds ranged between 32.7–423 μM against hCA I, 2.13–32.4 μM against hCA II, 13.7–234 μM against hCA IV and 76–278 μM against CA VI, respectively. The sulfatase activity of CA with such esters is amazing considering the fact that 4-nitrophenyl-sulfate is not a substrate of these enzymes.

NO-releasing esters show carbonic anhydrase inhibitory action against human isoforms I and II

Carbonic anhydrase (CA, EC 4.2.1.1) inhibitors (CAIs) are a class of pharmaceuticals used as antiglaucoma agents, diuretics, antiepileptics, in the management of mountain sickness, gastric and duodenal ulcers, neurological disorders, or osteoporosis. We report here the inhibitory capacities of some organic nitrates against two human (hCA) isozymes, hCA I and hCA II. The IC(50) values of compounds 1-12 against hCA I ranged between 7.13mM and 124mM, and against hCA II between 65.1microM and 0.79mM. Nitrate esters are thus interesting hCA I and II inhibitors, and might be used as leads for generating enzyme inhibitors eventually targeting other isoforms which have not been assayed yet for their interactions with such agents.

Structure-activity relationships for the interaction of 5,10-dihydroindeno[1,2-b]indole derivatives with human and bovine carbonic anhydrase isoforms I, II, III, IV and VI

Several 5,10-dihydroindeno[1,2-b]indole derivatives incorporating methoxy, hydroxyl, and halogen (F, Cl, and Br) moieties on the indene fragment of the molecule were prepared and tested against five carbonic anhydrase (CA, EC 4.2.1.1) isoforms. The inhibitory potencies of these compounds against the human (h) isoforms hCA I, II, IV, VI and bovine (b) isoform bCA III were assessed. Most of them exhibited low micromolar inhibition of these enzymes. K(I) values of these compounds against hCA I and hCA II were in the range of 2.14-16.32 μM, and 0.34-2.52 μM, respectively. Isozyme hCA IV was inhibited with K(I)-s in the range of 0.435-5.726 μM, while hCA VI with K(I)-s of 1.92-12.84 μM bCA III was inhibited with K(I)-s in the range of 2.13-17.83 μM. The structurally related compounds, 1,2-dimethoxybenzene, catechol and indole were also tested in order to understand the structure activity relationship. In silico docking studies of some derivatives within the active site of hCA I and II were also carried out in order to rationalize the inhibitory properties of these compounds and understand their inhibition mechanism.

In vitro inhibition of human erythrocyte glutathione reductase by some new organic nitrates

Glutathione reductase (GR), is responsible for the existence of GSH molecule, a crucial antioxidant against oxidative stress reagents. The antimalarial activities of some redox active compounds are attributed to their inhibition of antioxidant flavoenzyme glutathione reductase, and inhibitors are therefore expected to be useful for the treatment of malaria. Twelve organic nitrate derivatives were synthesized and treated with human erythrocyte GR. The molecules were identified as strong GR inhibitors and novel antimalaria candidates.

Synthesis of an amine-functionalized naphthalene-containing conducting polymer as a matrix for biomolecule immobilization

N-functionalized dithienopyrroles (DTP-NH2) were synthesized and electropolymerized onto a graphite electrode as a novel conducting polymer matrix for biomolecule immobilization. 1H-NMR and 13C-NMR were utilized to investigate the characteristics of the monomer. After that, glucose oxidase (GOx) was immobilized onto the amino-functionalised matrix by means of glutaraldehyde. The surface morphologies of both DTP-NH2 and DTP-NH2–GOx were visualised by using SEM and fluorescence microscopy. The chronoamperometric signals of the electrochemical DTP-NH2–GOx biosensors were measured by monitoring the O2 consumption during an enzymatic reaction in the presence of glucose at −0.7 V. After the optimization of the pH and scan number of the polymer deposition in batch mode, the DTP-NH2–GOx biosensor was also tested in Flow Injection Analysis (FIA) mode. The DTP-NH2–GOx biosensors had a very good linearity between 0.05 and 1.0 mM, and between 0.1 and 2.5 mM for glucose in batch and FIA modes, respectively. Finally, it was applied for glucose analysis in real samples where commercial glucose kits were used as the reference method to verify the data obtained with the proposed biosensor.

Synthesis of 1,4-bis(indolin-1-ylmethyl)benzene derivatives and their structure-activity relationships for the interaction of human carbonic anhydrase isoforms I and II.

Several 1,4-bis(indolin-1-ylmethyl)benzene-based compounds containing substituents such as five, six and seven cyclic derivatives on indeno part (9a-c) were prepared and tested against two members of the pH regulatory enzyme family, carbonic anhydrase (CA). The inhibitory potencies of the compounds at the human isoforms hCA I and hCA II targets were analyzed and KI values were calculated. KI values of compounds for hCA I and hCA II human isozymes were measured in the range of 39.3-42.6μM and 0.17-0.29μM, respectively. The structurally related compound indole was also tested in order to understand the structure-activity relationship. Most of the compounds showed good CA inhibitory efficacy. In silico docking studies of these derivatives within hCA I and II were also carried out and results are supported the kinetic assays.

Synthesis of 3,4-dihydroxypyrrolidine-2,5-dione and 3,5-dihydroxybenzoic acid derivatives and evaluation of the carbonic anhydrase I and II inhibition.

Abstract The inhibition of two human cytosolic carbonic anhydrase (hCA, EC 4.2.1.1) isozymes I and II, with some 3,4-dihydroxypyrrolidine-2,5-dione and 3,5-dihydroxybenzoic acid derivatives, were investigated by using the esterase assay, with 4-nitrophenyl acetate (4-NPA) as substrate. Compounds 10–13 showed KI values in the range of 112.7–441.5 μM for hCA I and of 3.5–10.76 μM against hCA II, respectively. These hydroxyl group containing compounds generally were competitive inhibitors. Some hydroxyl group containing compounds investigated here showed effective hCA II inhibitory effects, in the same range as the clinically used sulfonamide acetazolamide, and might be used as leads for generating enzyme inhibitors possibly targeting other CA isoforms which have not been yet assayed for their interactions with such agents.

Novel Photoelectrochemical Biosensors for Cholesterol Biosensing by Photonic “Wiring” of Cholesterol Oxidase

In this study, a novel approach for constructing different very sensitive and efficient photoelectrochemical biosensors called as P(SNS-NH2)/ChOx/[Ru(bpy)3]2+ and ChOx/[Ru(bpy)3]2+, were fabricated by bonding ChOx covalently to P(SNS-NH2) modified electrode and bare thioaniline modififed gold slide, respectively, using gluteraldehyde and tethering the N-hydroxysuccinimidyl ester functionalized Ru(II)-trisbipryridine to the ChOx enzyme. In the presence of different concentrations of cholesterol, the photocurrents were obtained by irradiating of the photoelectrochemical cell containing P(SNS-NH2)/ChOx/[Ru(bpy)3]2+ or ChOx/[Ru(bpy)3]2+ electrode as the anode under air. The bipyridine complex [Ru(bpy)3]2+ was used to activate photoinduced electron-transfer reaction and it acted as a redox mediator to activate the bioelectrocatalytic functions of ChOx. Therefore, it was shown the photonic electron-transfer wiring of ChOx with the electrode. ChOx/[Ru(bpy)3]2+ and P(SNS-NH2)/ChOx/[Ru(bpy)3)2+ biosensors showed a very good linearity between 0.05–0.9 mM and 0.00625–0.6 mM for cholesterol respective. LOD values for P(SNS-NH2)/ChOx/[Ru(bpy)3)2+ and ChOx/[Ru(bpy)3)2+ electrodes were obtained as 9.86 × 10−5 mM and 3.48 × 10−4 mM cholesterol respectively according to S/N = 3 ratios. Kinetic parameters, such as Km and Imax operational and storage stabilities, effects of pH and temperature were determined for both enzyme electrodes.

Synthesis of novel mono and bis-indole conduritol derivatives and their α/β-glycosidase inhibitory effects.

Here we synthesized four novel indole conduritol derivatives 1-4 for the first time in the literature and probed their biological activities with the α and β-glucosidases. The compounds showed quite effective glucosidase inhibitory action. IC(50) values of the compounds were compared with the known glucosidase inhibitor acarbose and it was determined that newly synthesized indole conduritols had more powerful effect against β-glucosidase in addition to exhibiting moderate influence against α-glucosidase. Our molecules thus constitute an important starting point for the design and exploitation of novel glucosidase inhibitors since glucosidase inhibitors have widespread applications in the treatment of diabetes, viral infections, lysosomal storage diseases and cancers.

Carbonic Anhydrase Inhibitors and Activators: Small Organic Molecules as Drugs and Prodrugs

This chapter concerns influences of inhibitors and activators on carbonic anhydrase isoenzymes of various living systems. Carbonic anhydrase (EC 4.2.1.1., CA) is a pH regulatory/metabolic enzyme in all life kingdoms, found in organisms all over the phylogenetic tree (Supuran, 2008a,b,c) catalyzing the hydration of carbon dioxide to bicarbonate and the corresponding dehydration of bicarbonate in acidic medium with regeneration of CO2 (Sly and Hu, 1995). 16 isozymes have been described up to now in mammals, the most active ones as catalysts for carbon dioxide hydration being CA II and CA IX (Sly and Hu, 1995; Ozensoy et al., 2004; Bayram et al., 2008; Senturk et al., 2009; Hilvo et al, 2008). The sixteen isozymes differ in their subcellular localization, catalytic activity and susceptibility to different classes of inhibitors. Some of them are cytosolic (CA I, CA II, CA III, CA VII and CA XIII), others are membrane bound (CA IV, CA IX, CA XII and CA XIV), two are mitochondrial (CA VA and CA VB), and one is secreted in saliva (CA VI). It has been reported that CA XV isoform is not expressed in humans or in other primates, but it is abundant in rodents and other vertebrates (Table 1.) (Nair et al., 1994; Parkkila et al., 1996; Pastorekava et al., 2004; Bayram et al., 2008; Innocenti et al., 2008a,b; Senturk et al., 2009; Ekinci et al., 2011). CAs are produced in a variety of tissues where they participate in several important biological processes such as acid-base balance, respiration, carbon dioxide and ion transport, bone resorption, ureagenesis, gluconeogenesis, lipogenesis and body fluid generation (Supuran, 2008a,b,c). CA isozymes involved in these processes are important therapeutic targets with the potential to be inhibited / activated for the treatment of a range of disorders such as edema, glaucoma, obesity, cancer, epilepsy and osteoporosis (Innocenti et al., 2008b; Ekinci et al., 2007; Ekinci et al., 2011).