Pablo A. Nogara

Virtual screening of acetylcholinesterase inhibitors using the Lipinski's rule of five and ZINC databank.

Alzheimers disease (AD) is a progressive and neurodegenerative pathology that can affect people over 65 years of age. It causes several complications, such as behavioral changes, language deficits, depression, and memory impairments. One of the methods used to treat AD is the increase of acetylcholine (ACh) in the brain by using acetylcholinesterase inhibitors (AChEIs). In this study, we used the ZINC databank and the Lipinskis rule of five to perform a virtual screening and a molecular docking (using Auto Dock Vina 1.1.1) aiming to select possible compounds that have quaternary ammonium atom able to inhibit acetylcholinesterase (AChE) activity. The molecules were obtained by screening and further in vitro assays were performed to analyze the most potent inhibitors through the IC50 value and also to describe the interaction models between inhibitors and enzyme by molecular docking. The results showed that compound D inhibited AChE activity from different vertebrate sources and butyrylcholinesterase (BChE) from Equus ferus (EfBChE), with IC50 ranging from 1.69 ± 0.46 to 5.64 ± 2.47 µM. Compound D interacted with the peripheral anionic subsite in both enzymes, blocking substrate entrance to the active site. In contrast, compound C had higher specificity as inhibitor of EfBChE. In conclusion, the screening was effective in finding inhibitors of AChE and BuChE from different organisms.

Molecular Docking Studies of Disubstituted Diaryl Diselenides as Mammalian δ-Aminolevulinic Acid Dehydratase Enzyme Inhibitors

δ-Aminolevulinic acid dehydratase (δ-ALAD) is a metalloprotein that catalyzes porphobilinogen formation. This enzyme is sensitive to pro-oxidants and classically used as a biomarker of lead (Pb) intoxication. Diphenyl diselenide [(PhSe)2] and analogs bis(4-chlorophenyl) diselenide [(pCl3PhSe)2], bis(4-methoxyphenyl)diselenide [(pCH3OPhSe)2], and bis[3-(trifluoromethy)phenyl] diselenide [(mCF3PhSe)2] inhibit mammalian δ-ALAD by oxidizing enzyme cysteinyl residues, which are involved in diselenide-induced toxicity. 2-Cysteinyl residues from δ-ALAD are believed to sequentially interact with (PhSe)2. Thus this study utilized protein–ligand docking analyses to determine which cysteinyl residues might be involved in the inhibitory effect of (PhSe)2 and analogs toward δ-ALAD. All diselenides that interact in a similar manner with the active site of δ-ALAD were examined. Docking simulations indicated an important role for π–π interactions involving Phe208 and cation–π interactions involving Lys199 and Arg209 residues with the aromatic ring of (PhSe)2 and analogs. Based upon these interactions an approximation between Se atoms and –SH of Cys124, with distances ranging between 3.3 Å and 3.5 Å, was obtained. These data support our previous postulations regarding the mechanism underlying δ-ALAD oxidation mediated by (PhSe)2 and analogs. Based on protein–ligand docking analyses, data indicated that –SH of Cys124 attacks one of the Se atoms of –SH of (PhSe)2 releasing one PhSeH (selenophenol). Subsequently, the –SH of Cys132 attacks the sulfur atom of Cys124 (from the bond of E-S-Se-Ph indermediate), generating the second PhSe–, and the oxidized and inhibited δ-ALAD. In conclusion, AutoDock Vina 1.1.1 was a useful tool to search for diselenides inhibitors of δ-ALAD, and, most importantly, it provided insight into molecular mechanisms involved in enzyme inhibition.

Effect of Different Oximes on Rat and Human Cholinesterases Inhibited by Methamidophos: A Comparative In Vitro and In Silico Study

Methamidophos is one of the most toxic organophosphorus (OP) compounds. It acts via phosphorylation of a serine residue in the active site of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), leading to enzyme inactivation. Different oximes have been developed to reverse this inhibition. Thus, our work aimed to test the protective or reactivation capability of pralidoxime and obidoxime, as well as two new oximes synthesised in our laboratory, on human and rat cholinesterases inhibited by methamidophos. In addition, we performed molecular docking studies in non‐aged methamidophos‐inhibited AChE to understand the mechanisms involved. Our results suggested that pralidoxime protected and reactivated methamidophos‐inhibited rat brain AChE. Regarding human erythrocyte AChE, all oximes tested protected and reactivated the enzyme, with the best reactivation index observed at the concentration of 50 μM. Concerning BChE, butane‐2,3‐dionethiosemicarbazone oxime (oxime 1) was able to protect and reactivate the methamidophos‐inhibited BChE by 45% at 50 μM, whereas 2(3‐(phenylhydrazono)butan‐2‐one oxime (oxime 2) reactivated 28% of BChE activity at 100 μM. The two classical oximes failed to reactivate BChE. The molecular docking study demonstrated that pralidoxime appears to be better positioned in the active site to attack the O‐P moiety of the inhibited enzyme, being near the oxyanion hole, whereas our new oximes were stably positioned in the active site in a manner similar to that of obidoxime. In conclusion, our work demonstrated that the newly synthesised oximes were able to reactivate not only human erythrocyte AChE but also human plasma BChE, which could represent an advantage in the treatment of OP compounds poisoning.

Synthesis and antinociceptive activity of new 2-substituted 4-(trifluoromethyl)-5,6-dihydrobenzo[h]quinazolines

A useful synthetic route for an initial new series of 2-substituted 4-(trifluoromethyl)-5,6-dihydrobenzo[h]quinazolines (3), as well as an evaluation of their analgesic effect in a mice pain model, is reported. Five new quinazolines were formed from the cyclocondensation reactions of 2,2,2-trifluoro-1-(1-methoxy-1,2,3,4-tetrahydronaphthalen-2-yl)ethanone (1) with some well-known amidine salts [NH2CR(=NH)] (2), in which R=H, Me, Ph, NH2 and SMe, at a 40-70% yield. Subsequently, due to the importance of the pyrrole nucleus, a 2-(pyrrol-1-yl)quinazoline (4) was obtained through a Clauson-Kaas reaction from the respective 2-(amino)quinazoline, in a reaction with 2,5-dimethoxy-tetrahydrofuran. The analgesic evaluation demonstrated that four 5,6-dihydrobenzo[h]quinazolines (compounds of 3c (R=Ph), 3d (R=NH2), 3e (R=SMe), and 4 (R=pyrrol-1-yl); 100mg/kg, p.o.) and ketoprofen (100mg/kg, p.o.) significantly reduced the spontaneous nociception in a capsaicin-induced test. Moreover, in comparison with ketoprofen (100 and 300mg/kg, p.o.), compound 3c (30-300mg/kg, p.o.) showed an anti-hyperalgesic action in an arthritic pain model without locomotor alterations in the mice, suggesting that quinazoline 3c is a promising prototype scaffold for new analgesic drugs in the treatment of pathological pain such as that in arthritis.

In Silico Studies of Mammalian δ‐ALAD Interactions with Selenides and Selenoxides

Previous studies have shown that the mammalian δ‐aminolevulinic acid dehydratase (δ‐ALAD) is inhibited by selenides and selenoxides, which can involve thiol oxidation. However, the precise molecular interaction of selenides and selenoxides with the active center of the enzyme is unknown. Here, we try to explain the interaction of selenides and the respective selenoxides with human δ‐ALAD by in silico molecular docking. The in silico data indicated that Se atoms of selenoxides have higher electrophilic character than their respective selenides. Further, the presence of oxygen increased the interaction of selenoxides with the δ‐ALAD active site by O…Zn coordination. The interaction of S atom from Cys124 with the Se atom indicated the importance of the nucleophilic attack of the enzyme thiolate to the organoselenium molecules. These observations help us to understand the interaction of target proteins with organoselenium compounds.Previous studies have shown that the mammalian δ-aminolevulinic acid dehydratase (δ-ALAD) is inhibited by selenides and selenoxides, which can involve thiol oxidation. However, the precise molecular interaction of selenides and selenoxides with the active center of the enzyme is unknown. Here, we try to explain the interaction of selenides and the respective selenoxides with human δ-ALAD by in silico molecular docking. The in silico data indicated that Se atoms of selenoxides have higher electrophilic character than their respective selenides. Further, the presence of oxygen increased the interaction of selenoxides with the δ-ALAD active site by O…Zn coordination. The interaction of S atom from Cys124 with the Se atom indicated the importance of the nucleophilic attack of the enzyme thiolate to the organoselenium molecules. These observations help us to understand the interaction of target proteins with organoselenium compounds.

1,1-Difluoro-3-aryl(heteroaryl)-1H-pyrido[1,2-c][1,3,5,2]oxadiazaborinin-9-ium-1-uides: synthesis; structure; and photophysical, electrochemical, and BSA-binding studies

This paper presents a series of six examples of 1,1-difluoro-3-aryl(heteroaryl)-1H-pyrido[1,2-c][1,3,5,2]oxadiazaborinin-9-ium-1-uides (2)—in which aryl(heteroaryl) = phenyl, 4-MeC6H4, 4-N(CH3)2C6H4, 4-NO2C6H4, 2-naphthyl, and 2-thienyl—as pyridine-based boron heterocycles with variable ligand structures. The heterocycles 2 were easily synthesized at yields of 51–70% from reactions—at room temperature for 24 h—of simple N-(pyridin-2-yl)benzamides (1) with BF3·Et2O, and they were fully characterized by 1H-, 13C-, 19F-, and 11B-NMR spectroscopy, GC-MS, and X-ray diffractometry. The optical and electrochemical properties of 2 (UV-vis spectra, fluorescence spectra, quantum yield calculations, Stokes’ shifts, redox potentials, and DFT calculations) were determined and discussed. BSA-binding experiments and molecular docking studies of new complexes 2 were performed and correlated between each other.

Cytotoxic and Tripanocide Activities of Pityrogramma calomelanos (L.) Link

Abstract Chagas disease is caused by Trypanosoma cruzi, and is considered a public health problem. The current treatments for this disease are the synthetic drugs nifurtimox and benzonidazol, which are highly toxic. Pityrogramma calomelanos, a plant used in traditional medicine as an astringent, analgesic, anti-hemorrhagic, pectoral depurative, emmenagogue, anti-hypertensive, anti-pyretic and an anti-tussive was tested for antiepimastigote activity in vitro. An ethanol extract and hexane fraction of P. calomelanos was prepared and tested against T. cruzi (CL-B5 clone). The effective concentration capable of killing 50% of parasites (EC50) was 55.26 µg/mL and 73.57 µg/mL for the ethanol extract and hexane fraction, respectively. This is the first record of tripanocidal activity for P. calomelanos. Our results indicate that P. calomelanos could be a source of antiepimastigote natural products with only moderate toxicity toward healthy human cells.

O hormônio insulina como um modelo para ensinar a estrutura tridimensional das proteínas

Proteins are the most ubiquitous macromolecules found in the living cells and have severals physiological functions. Therefore, it is fundamental to build a solid knowledge about the proteins three-dimensional structure to better understand the living state. The hierarchical structure of proteins is usually studied in the undergraduate discipline of Biochemistry. Here we described pedagogical interventions designed to increase the pre-service teacher chemistry students’ knowledge about protein structure. The activities were made using alternative and cheap materials to encourage the application of these simple methodologies by the future teachers in the secondary school. From the primary structure of insulin chains, students had to construct a three-dimensional structure of insulin. After the activities, the students highlighted an improvement of their previous knowledge about proteins structure. The construction of a three-dimensional model together with other activities seems to be an efficient way to promote the learning about the structure of proteins to undergraduate students. The methodology used was inexpensive and simple and it can be used both in the university and in the high-school.

Lophine and pyrimidine based photoactive molecular hybrids. Synthesis, photophysics, BSA interaction and DFT study

Two photoactive molecular hybrids containing both lophine and pyrimidine moieties were synthesized by multicomponent reaction. The compounds present absorption in the UV-region (below 300 nm) and fluorescence emission in the violet region due to the lophine moiety. Experimental evidence indicates that photoinduced electron transfer (PET) occurs in the excited state of the hybrids. The observed photophysical features were successfully used to explore the interaction of the compounds with bovine serum albumin (BSA) in phosphate buffer solution (PBS) where a significant suppression mechanism was observed for both molecular hybrids. The DFT and TD-DFT calculations were performed at the ωB97XD level of theory. The results show low influence of the solvent on the wavelengths. However, the dipole moment undergoes a significant modification when the solvent is changed, showing a high polar behavior towards the excited state. Calculations also show us that the excitation is local, and that there is no charge transfer.

A New Protocol for the Synthesis of New Thioaryl-Porphyrins Derived from 5,10,15,20-Tetrakis(pentafluorophenyl)porphyrin: Photophysical Evaluation and DNA-Binding Interactive Studies

A new protocol for the preparation of thioaryl-porphyrins is described. The compounds were prepared from different disulfides employing NaBH4 as a reducing agent. The methodology allowed the preparation of four different thioaryl-porphyrins in very-good to excellent yields under soft conditions, such as short reaction times and smooth heating. Additionally, the photophysical properties of new compounds were determined and experimental and theoretical DNA interactions were assessed.