Esteban G. Vega-Hissi

Theoretical studies on sulfanilamide and derivatives with antibacterial activity: conformational and electronic analysis

AbstractQuantum chemical methods have been used to study the conformational and electronic properties of sulfanilamide and derivatives with antibacterial activity. Calculations at B3LYP/6-311++G(3df,2p) level of theory predict the existence of four conformers for sulfanilamide depending on the orientation of p-amino and amide groups. Focusing on the sulfonamide moiety, amide NH2 and SO2 groups could exist either in an eclipsed or staggered arrangement. Gas-phase results predict the eclipsed conformer to be most stable but opposite to what has been rationalized previously, no stabilizing hydrogen bonds between those groups has been found through NBO analysis. When solvent effect is taken into account through the IEF-PCM method, staggered conformer is preferred; in fact, eclipsed conformation changed when explicit solvent molecules were included. Conformational analysis of all derivatives has shown two global minima which are specular images. Five out of the seven derivatives studied adopted a particular minimum energy conformation with very similar geometries. FigureAntibacterial sulfonamides show a large conformational similarity degree.

Computational chemical analysis of unconjugated bilirubin anions and insights into pKa values clarification

The pKa, the negative logarithm of the acid dissociation equilibrium constant, of the carboxylic acid groups of unconjugated bilirubin in water is a discussed issue because there are quite different experimental values reported. Using quantum mechanical calculations we have studied the conformational behavior of unconjugated bilirubin species (in gas phase and in solution modeled implicitly and explicitly) to provide evidence that may clarify pKa values because of its pathophysiological relevance. Our results show that rotation of carboxylate group, which is not restricted, settles it in a suitable place to establish stronger interactions that stabilizes the monoanion and the dianion to be properly solvated, demonstrating that the rationalization used to justify the high pKa values of unconjugated bilirubin is inappropriate. Furthermore, low unconjugated bilirubin (UCB) pKa values were estimated from a linear regression analysis.

Dihydrofolate reductase inhibitors: a quantitative structure–activity relationship study using 2D-QSAR and 3D-QSAR methods

In this work, we study the structure–activity relationship of a series of Dihydrofolate reductase inhibitors by two-dimensional quantitative activity–structure relationship and three-dimensional quantitative activity–structure relationship techniques. The two-dimensional quantitative activity–structure relationship models were developed by using two different types of topological molecular descriptors, PaDEL and Dragon descriptors. The models showed an excellent predictive power, R2train = 0.916 and R2val = 0.806 for the PaDEL, and R2train = 0.952 and R2val = 0.963 for those obtained with Dragon descriptors. Simple molecular descriptors as maxHCsats, IC3, SPI, SIC2, and GATS5p were adequate to obtain predictive models. The three-dimensional quantitative activity–structure relationship was performed through three variable selected approaches, Partial Linear Square (PLS), Fractional Factorial Design (FFD) and Uninformative Variable Elimination-Partial Linear Square (UVE-PLS) using the Open3DQSAR software. All the 2D and 3D models were validated using two compounds (number 24 and 25), which were synthesized and presented here for the first time. Their biological activities were correctly predicted by all the quantitative activity–structure relationship models. Finally, we proposed three compounds (26, 27, and 28), which showed a high predicted Dihydrofolate reductase inhibitory activity. Molecular docking study suggested that compounds bind to receptor similarly to the most active inhibitors.

Lacosamide Derivatives with Anticonvulsant Activity as Carbonic Anhydrase Inhibitors. Molecular Modeling, Docking and QSAR Analysis

Lacosamide is an anticonvulsant drug which presents carbonic anhydrase inhibition. In this paper, we analyzed the apparent relationship between both activities performing a molecular modeling, docking and QSAR studies on 18 lacosamide derivatives with known anticonvulsant activity. Docking results suggested the zinc-binding site of carbonic anhydrase is a possible target of lacosamide and lacosamide derivatives making favorable Van der Waals interactions with Asn67, Gln92, Phe131 and Thr200. The mathematical models revealed a poor relationship between the anticonvulsant activity and molecular descriptors obtained from DFT and docking calculations. However, a QSAR model was developed using Dragon software descriptors. The statistic parameters of the model are: correlation coefficient, R=0.957 and standard deviation, S=0.162. Our results provide new valuable information regarding the relationship between both activities and contribute important insights into the essential molecular requirements for the anticonvulsant activity.

QSAR and 3D-QSAR studies applied to compounds with anticonvulsant activity

Introduction: Quantitative structure–activity relationships (QSAR and 3D-QSAR) have been applied in the last decade to obtain a reliable statistical model for the prediction of the anticonvulsant activities of new chemical entities. However, despite the large amount of information on QSAR, no recent review has published and discussed this data in detail. Areas covered: In this review, the authors provide a detailed discussion of QSAR studies that have been applied to compounds with anticonvulsant activity published between the years 2003 and 2013. They also evaluate the mathematical approaches and the main software used to develop the QSAR and 3D-QSAR model. Expert opinion: QSAR methodologies continue to attract the attention of researchers and provide valuable information for the development of new potentially active compounds including those with anticonvulsant activity. This has been helped in part by improvements in the size and performance of computers; the development of specific software and the development of novel molecular descriptors, which have given rise to new and more predictive QSAR models. The extensive development of descriptors, and the way by which descriptor values are derived, have allowed the evolution of the QSAR methods. This evolution could strengthen the QSAR methods as an important tool in research and development of new and more potent anticonvulsant agents.

In Silico Modeling of the Molecular Structure and Binding of Leukotriene A4 into Leukotriene A4 Hydrolase

A combined molecular docking and molecular structure in silico analysis on the substrate and product of leukotriene A4 hydrolase (LTA4H) was performed. The molecular structures of the substrate leukotriene A4 (LTA4) and product leukotirene B4 (LTB4) were studied through density functional theory (DFT) calculations at the B3LYP/6‐31 + G(d) level of theory in both gas and condensed phases. The whole LTB4 molecule was divided into three fragments (hydrophobic tail, triene motif, and a polar acidic group) that were subjected to a full conformational study employing the most stable conformations of them to build conformers of the complete molecule and geometry optimize further. LTA4 conformers’ structures were modeled from the LTB4 minimum energy conformers. Both protonated and deprotonated species of LTA4 and LTB4 were analyzed according to pKa values found in the literature. Finally, a binding model of LTA4 with LTA4 hydrolase is proposed according to docking results that show intermolecular interactions that position the protonated and deprotonated ligand in the active site, in excellent agreement with the model suggested from LTA4H‐inhibitors crystallographic data.

Density functional theory study of the oxidation reaction in the gas and aqueous phase of allyl methyl disulfide with hydroxyl radical

An in silico analysis of the oxidation mechanism of allyl methyl disulfide (AMDS) by hydroxyl radical was achieved at DFT level using B3LYP, CAM-B3LYP, M06-2X, and BMK functionals and 6-311++G(3df,2p) triple-zeta basis set. The calculations were carried out in both gas and aqueous phases using the SMD model (density-based solvation model). Three potential reactions were proposed according to results of Fukui function; in reactions 1 and 2, the hydroxyl radical attacks the sulfur atom breaking the disulfide bond and the reaction 3 is a hydrogen atom subtraction reaction. The respective structures of transition states (TSs) were found. Intrinsic reaction coordinate (IRC) calculations were performed for the three reactions, and their rates and equilibrium constants were calculated. When the solvent effect is taken into account, the four DFT functionals employed designate R3 (a subtraction reaction) as the fastest reaction. Thus, we elucidated the thermodynamic and kinetic feasibility of the proposed oxidation reactions.