Combined Utilization Of H-1 Nmr, Ir, And Theoretical Calculations To Elucidate The Conformational Preferences Of Some L-histidine Derivatives

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)The conformational preferences of amino acids and their derivatives have been the subject of many investigations, because protein folding pathways that determine three-dimensional geometries are primarily restricted by the conformational space of each amino acid residue. Here we systematically describe the conformational behavior of L-histidine methyl ester (HisOMe) and its N-acetylated derivative (AcHisOMe) in the isolated phase and in solution. To this end, we employed spectroscopic techniques (H-1 NMR and IR), supported by quantum chemical calculations. Initially, the energetically favorable conformers, their energies, and structural properties obtained by density functional theory (DFT) and MollerPlesset perturbation theory (MP2) calculations in the isolated phase and in solution via the implicit solvation model IEF-PCM were presented. Next, experimental (3)J(HH) spinspin coupling constants obtained in different aprotic nonpolar and polar solvents were compared with the theoretically predicted ones for each conformer at the IEF-PCM/omega B97X-D/EPR-III level. A joint analysis of these data allowed the elucidation of the conformational preferences of the compounds in solution. Infrared data were also employed as a complement to estimate the HisOMe conformer populations. Finally, the quantum theory of atoms in molecules (QTAIM), the noncovalent interactions (NCI), and the natural bond orbitals (NBO) analyses were used to determine the intramolecular interactions that govern the relative conformational stabilities.1213729740Sao Paulo Research Foundation (FAPESP) [2014/25903-6, 2012/18567-4]Conselho Nacional de Pesquisa (CNPQ)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq

Experimental And Theoretical Evaluation On The Conformational Behavior Of L-aspartic Acid Dimethyl Ester And Its N-acetylated Derivative

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)In this work the conformational preferences of L-aspartic acid dimethyl ester (AspOMe) and its N-acetylated derivative (AcAspOMe) were evaluated through spectroscopic data and theoretical calculations. Unlike amino acids, their corresponding amino ester derivatives do not exhibit a zwitterionic structure and are soluble in most organic solvents, enabling their studies in these media. Thus, the conformers of AspOMe and AcAspOMe were theoretically determined both in isolated phase and in solution (IEF-PCM model) at the omega B97X-D/aug-cc-pVTZ level. A joint analysis of the experimental and theoretical (3)J(HH) coupling constants in several aprotic solvents allowed assigning the most stable conformers, showing excellent agreement between these approaches. Also, IR spectroscopy allowed us to obtain quantitative data on AcAspOMe conformer populations in different solvents. Natural bond orbital (NBO) analysis indicated that both steric and hyperconjugative contributions count in determining the relative conformer stabilities of these compounds. Intramolecular hydrogen bonding, characterized by Quantum Theory of Atoms in Molecules (QTAIM) and Non-Covalent Interactions (NCI) methodologies, represents only a secondary factor to drive the stabilities of AspOMe and AcAspOMe conformers.5231801318024Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)FAPESP [2012/03933-5, 2012/18567-4

Combined Utilization of ¹H NMR, IR, and Theoretical Calculations To Elucidate the Conformational Preferences of Some l‑Histidine Derivatives

The conformational preferences of amino acids and their derivatives have been the subject of many investigations, because protein folding pathways that determine three-dimensional geometries are primarily restricted by the conformational space of each amino acid residue. Here we systematically describe the conformational behavior of l-histidine methyl ester (His–OMe) and its <i>N</i>-acetylated derivative (Ac–His–OMe) in the isolated phase and in solution. To this end, we employed spectroscopic techniques (¹H NMR and IR), supported by quantum chemical calculations. Initially, the energetically favorable conformers, their energies, and structural properties obtained by density functional theory (DFT) and Møller–Plesset perturbation theory (MP2) calculations in the isolated phase and in solution via the implicit solvation model IEF-PCM were presented. Next, experimental ³<i>J</i>_HH spin–spin coupling constants obtained in different aprotic nonpolar and polar solvents were compared with the theoretically predicted ones for each conformer at the IEF-PCM/ωB97X-D/EPR-III level. A joint analysis of these data allowed the elucidation of the conformational preferences of the compounds in solution. Infrared data were also employed as a complement to estimate the His–OMe conformer populations. Finally, the quantum theory of atoms in molecules (QTAIM), the noncovalent interactions (NCI), and the natural bond orbitals (NBO) analyses were used to determine the intramolecular interactions that govern the relative conformational stabilities

Experimental and theoretical evaluation on the conformational behavior of L-aspartic acid dimethyl ester and Its N-acetylated derivative

In this work the conformational preferences of L-aspartic acid dimethyl ester (AspOMe) and its N-acetylated derivative (AcAspOMe) were evaluated through spectroscopic data and theoretical calculations. Unlike amino acids, their corresponding amino ester derivatives do not exhibit a zwitterionic structure and are soluble in most organic solvents, enabling their studies in these media. Thus, the conformers of AspOMe and AcAspOMe were theoretically determined both in isolated phase and in solution (IEF-PCM model) at the omega B97X-D/aug-cc-pVTZ level. A joint analysis of the experimental and theoretical (3)J(HH) coupling constants in several aprotic solvents allowed assigning the most stable conformers, showing excellent agreement between these approaches. Also, IR spectroscopy allowed us to obtain quantitative data on AcAspOMe conformer populations in different solvents. Natural bond orbital (NBO) analysis indicated that both steric and hyperconjugative contributions count in determining the relative conformer stabilities of these compounds. Intramolecular hydrogen bonding, characterized by Quantum Theory of Atoms in Molecules (QTAIM) and Non-Covalent Interactions (NCI) methodologies, represents only a secondary factor to drive the stabilities of AspOMe and AcAspOMe conformers5231801318024CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESPsem informação2012/03933-5; 2012/18567-

Biodegradable and ph-responsive acetalated dextran (Ac-Dex) nanoparticles for nir imaging and controlled delivery of a platinum-based prodrug into cancer cells

Nanoparticles (NPs) based on the biodegradable acetalated dextran polymer (Ac-Dex) were used for near-infrared (NIR) imaging and controlled delivery of a PtIV prodrug into cancer cells. The Ac-Dex NPs loaded with the hydrophobic PtIV prodrug 3 (PtIV/Ac-Dex NPs) and with the novel hydrophobic NIR-fluorescent dye 9 (NIR-dye 9/Ac-Dex NPs), as well as Ac-Dex NPs coloaded with both compounds (coloaded Ac-Dex NPs), were assembled using a single oil-in-water nanoemulsion method. Dynamic light scattering measurements and scanning electron microscopy images showed that the resulting Ac-Dex NPs are spherical with an average diameter of 100 nm, which is suitable for accumulation in tumors via the enhanced permeation and retention effect. The new nanosystems exhibited high drug-loading capability, high encapsulation efficiency, high stability in physiological conditions, and pH responsiveness. Drug-release studies clearly showed that the PtIV prodrug 3 release from Ac-Dex NPs was negligible at pH 7.4, whereas at pH 5.5, this compound was completely released with a controlled rate. Confocal laser scanning microscopy unambiguously showed that the NIR-dye 9/Ac-Dex NPs were efficiently taken up by MCF-7 cells, and cytotoxicity assays against several cell lines showed no significant toxicity of blank Ac-Dex NPs up to 1 mg mL–1. The IC50 values obtained for the PtIV prodrug encapsulated in Ac-Dex NPs were much lower when compared with the IC50 values obtained for the free PtIV complex and cisplatin in all cell lines tested. Overall, our results demonstrate, for the first time, that Ac-Dex NPs constitute a promising drug delivery platform for cancer therapy16520832094CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQCOORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPESFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP573913/2008-0Não tem2018/02093-0; 2017/06146-8; 2017/24488-3; 08/57906-3The authors gratefully acknowledge Sao Paulo Research Foundation—FAPESP (grant #2018/02093-0 for C.O.; fellowship #2017/06146-8 for C.B.B.; scholarship #2017/24488-3 for G.P.) and Coordination for the Improvement of Higher Education Personnel—CAPES (Ph.D. scholarship for T.B.B.) for the financial support. This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nivel Superior—Brasil (CAPES), finance code 001. We also thank the access to equipment and assistance provided by the National Institute of Science and Technology on Photonics Applied to Cell Biology (INFABIC) at the State University of Campinas; INFABIC is cofunded by Fundação de Amparo a Pesquisa do Estado de São Paulo (FAPESP) (08/57906-3) and Conselho Nacional de Desenvolvimento Cientifico e Tecnológico (CNPq) (573913/2008-0

Conformational preferences of N-acetyl-N-methylprolineamide in different media: a H-1 NMR and theoretical investigation

A comprehensive description on the conformational behaviour of small peptide models is of primary importance to elucidate polypeptide and protein structures and folding pathways. In this paper, an extensive conformational investigation of N-acetyl-N-methylprolineamide (Ac-Pro-NHMe) in both isolated phase and in solution is reported. The joint use of H-1 NMR spectroscopy and DFT calculations allowed to determine the most stable conformers of Ac-Pro-NHMe and to evaluate its conformational preferences in different media. Theoretical calculations at the M06-2X/aug-cc-pVTZ level of theory led to the identification of two and six stable conformers in isolated phase and solution, respectively. These geometries reveal the presence of two isomers, where the -NC(O)Me bond can assume a trans ( = 180 degrees) or cis ( = 0 degrees) orientation in relation to the -(CO)NHMe group of backbone. The theoretical results show that the trans,trans-IId in a down-puckered -turn-like structure and = 180 degrees, is the most populated conformer in isolated phase. In polar solvents, like acetonitrile and DMSO, there is a mixture of both polyproline II and -helix-like conformers, while in water, the trans,trans-IIu, in an up-puckered polyproline II-like geometry, is the less energetic. Therefore, our results show that conformer populations change upon solvent variation, indicating that the conformational equilibrium of Ac-Pro-NHMe is sensitive to solvent effects. The experimental population values, obtained through the integration of the peaks in the H-1 NMR spectrum, confirm the change of conformer populations in different solvents. The results reveal that the theoretical level employed in this study is in good agreement with experimental data. QTAIM and NCI analyses combined with orbital-based NBO calculations reveal that the conformers trans,trans-IId and trans,trans-IIu are stabilized by an intramolecular hydrogen bond (IHB) C?OHN in isolated phase. However, these geometries are completely destabilized in solution by the weakening of this interaction. Although IHB is essential to the stability of the two conformers in isolated phase, it represents only a secondary factor to the conformational preferences of the compound. The highest stability of trans,trans-IId in isolated phase can be attributed to hyperconjugative interactions. In solution, an interplay of hyperconjugative, steric and electrostatic effects rules the conformational preferences of Ac-Pro-NHMe43417571763CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQFUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP300821/2013-12016/24109-0; 2012/18567-4; 2016/12005-5

Conformational study of L-methionine and L-cysteine derivatives through quantum chemical calculations and 3JHH coupling constant analyses

The understanding of the conformational behavior of amino acids and their derivatives is a challenging task. Here, the conformational analysis of esterified and N-acetylated derivatives of L-methionine and L-cysteine using a combination of 1H NMR and electronic structure calculations is reported. The geometries and energies of the most stable conformers in isolated phase and taking into account the implicit solvent effects, according to the integral equation formalism polarizable continuum model (IEF−PCM), were obtained at the ωB97X-D/aug-cc-pVTZ level. The conformational preferences of the compounds in solution were also determined from experimental and theoretical 3JHH coupling constants analysis in different aprotic solvents. The results showed that the conformational stability of the esterified derivatives is not very sensitive to solvent effects, whereas the conformational equilibrium of the N-acetylated derivatives changes in the presence of solvent. According to the natural bond orbital (NBO), quantum theory of atoms in molecules (QTAIM) and noncovalent interactions (NCI) methodologies, the conformational preferences for the compounds are not dictated by intramolecular hydrogen bonding, but by a joint contribution of hyperconjugative and steric effects

Synthesis of nitrogen-containing goniothalamin analogues with higher cytotoxic activity and selectivity against cancer cells

Two series of racemic goniothalamin analogues displaying nitrogen-containing groups were designed and synthesized. A total of 19 novel analogues were evaluated against a panel of four different cancer cell lines, along with the normal prostate cell line PNT2 to determine their selectivity. Among them, goniothalamin chloroacrylamide 13 e displayed the lowest IC50 values for both MCF-7 (0.5 mu m) and PC3 (0.3 mu m) cells, about 26-fold more potent than goniothalamin (1). Besides its higher potency, compound 13 e also displayed much higher selectivity than goniothalamin. In contrast, goniothalamin isobutyramide 13 c was the most potent analogue against Caco-2 cells (IC50=0.8 mu m), about 10-fold more potent and 17-fold more selective than 1. These results reveal the potential of compounds 13 c and 13 e for further in vivo studies, representing the first goniothalamin analogues with IC50 values in the low micromolar range and high selectivity against MCF-7, Caco-2, and PC3 cancer cell lines141514031417CNPQ - Conselho Nacional de Desenvolvimento Científico e TecnológicoFAPESP – Fundação de Amparo à Pesquisa Do Estado De São Paulo2013/07607-8; 2018/02093-0134836/2016-

Conformational Analysis and Intramolecular Interactions of l‑Proline Methyl Ester and Its <i>N</i>‑Acetylated Derivative through Spectroscopic and Theoretical Studies

This work reports a detailed study regarding the conformational preferences of l-proline methyl ester (ProOMe) and its <i>N</i>-acetylated derivative (AcProOMe) to elucidate the effects that rule their behaviors, through nuclear magnetic resonance (NMR) and infrared (IR) spectroscopies combined with theoretical calculations. These compounds do not present a zwitterionic form in solution, simulating properly amino acid residues in biological media, in a way closer than amino acids in the gas phase. Experimental ³<i>J</i>_HH coupling constants and infrared data showed excellent agreement with theoretical calculations, indicating no variations in conformer populations on changing solvents. Natural bond orbital (NBO) results showed that hyperconjugative interactions are responsible for the higher stability of the most populated conformer of ProOMe, whereas for AcProOMe both hyperconjugative and steric effects rule its conformational equilibrium

Studies On The S-cis-trans Isomerism For Some Furan Derivatives Through Ir And Nmr Spectroscopies And Theoretical Calculations.

The s-cis-trans isomerism of two furan derivatives [2-acetyl- (AF) and 2-acetyl-5-methylfuran, (AMF)] was analyzed, using data from the deconvolution of their carbonyl absorption band in two solvents (CH(2)Cl(2) and CH(3)CN). These infrared data showed that the O,O-trans conformers predominate in the less polar solvent (CH(2)Cl(2)), but these equilibria change in a more polar solvent (CH(3)CN) leading to a slight predominance of the O,O-cis conformers, in agreement with the theoretical calculations. The later results were obtained using B3LYP-IEFPCM/6-31++g(3df,3p) level of theory, which taking into account the solvent effects at IEFPCM (Integral Equation Formalism Polarizable Continuum Model). Low temperature (13)CNMR spectra in CD(2)Cl(2) (ca. -75 °C) showed pairs of signals for each carbon, due to the known high energy barrier for the cis-trans interconversion leading to a large predominance of the trans isomers, which decreases in acetone-d(6). This was confirmed by their (1)HNMR spectra at the same temperatures. Moreover, despite the larger hyperconjugative interactions for the O,O-cis isomers, obtained from NBO data, these isomers are destabilized by the their Lewis energy.10384-