Revisiting the stability of endo/exo Diels-Alder adducts between cyclopentadiene and 1,4-benzoquinone

In this work it is presented a detailed theoretical analysis of the relative stability of endo/exo Diels-Alder adducts formed by the reaction between cyclopentadiene (1) and 1,4-benzoquinone (2). The intrinsic reaction coordinate (IRC) showed the existence of only one transition state for the reaction studied, for both endo 3 and exo 4 adducts. The energies of both adducts were obtained at high level of theory (CBS-Q) confirming that the endo adduct is more stable than exo, which is in the opposite way to the observed in reactions that usually follow Alder's rule. An electronic structure analysis was performed through NBO methodology, indicating that the attractive delocalization interaction predominates over the steric repulsive interaction in the endo adducts. In summary, for the studied cycloaddition reaction the endo adduct is the thermodynamic and kinetic product, which can be also confirmed by experimental data mentioned in this work

Identifying new isatin derivatives with GSK-3 inhibition capacity through molecular docking and bioassays

The semi-synthesis of 11 isatin derivatives was achieved through bimolecular nucleophilic substitution and click chemistry. Seven new compounds were obtained. All chemical structures were determined by infrared spectroscopy (IR), nuclear magnetic resonance spectrometry (NMR) and high-resolution mass spectrometry (HRMS) data. These derivatives were evaluated for their anti-GSK-3 activity and all isatin derivatives (N-alkyl and 1,2,3-triazolic) exhibited strong inhibitory activity, with 2b and 4h exhibiting remarkable potency. In addition, docking studies were performed with 2b and 2e models to unravel the molecular mechanism underlying the polar interactions on the GSK-3 ATP-binding site.This study was funded by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior, Brasil (CAPES), Finance Code 001, by the National Council of Scientific and Technological Development (CNPq) and Foundation of Support to Research and Innovation of Espírito Santo (FAPES PPE-Agro No. 76418880/16). We also would like to acknowledge INCTBioNat (CNPq 465637/2014-0) for additional support and NCQP-UFES, as well as the Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of UID/BIO/04469/2019 unit and BioTecNorte operation (NORTE-01-0145-FEDER-000004) funded by the European Regional Development Fund under the scope of Norte2020, Programa Operacional Regional do Norte. L. R. R. also acknowledges her sabbatical leave fellowship (SFRH/BSAB/142991/2018) funded by FCT. D. F. is recipient of a doctoral fellowship (call NORTE-69-2015-15) funded by the European Social Fund under the scope of Norte2020, Programa Operacional Regional do Norte.info:eu-repo/semantics/publishedVersio

Análise do teor e da qualidade dos lipídeos presentes em sementes de oleaginosas por rmn de baixo campo

To choose among the variety of oleaginous plants for biodiesel production, the oil content of several matrices was determined through different low-field ¹H nuclear magnetic resonance (NMR) experiments with varied pulse sequences, namely single-pulse, spin-echo, CPMG, and CWFP. The experiments that involved the first three sequences showed high correlation with each other and with the solvent extraction method. The quality of the vegetable oils was also evaluated on the basis of the existing correlation between the T2 values of the oils and their properties, such as viscosity, iodine index, and cetane index. These analyses were performed using HCA and PCA chemometric tools. The results were sufficiently significant to allow separation of the oleaginous matrices according to their quality. Thus, the low-field ¹H NMR technique was confirmed as an important tool to aid in the selection of oleaginous matrices for biodiesel production

Preparação de um Sinton Funcionalizado a Partir da Carvona Visando a Síntese de alfa-metileno-gama-butirolactonas Monoterpênicas

(R)-(-)-Carvone (6) has been transformed into oxygenated derivative 13, which is expected to be a useful synthon or chiral template in the synthesis of natural a-methylene-g-butyrolactones. This synthesis of compound 13 involves classics reactions of oxygenation in saturated carbon with full control of regioselectivity and stereoselectivity. DOI: http://dx.doi.org/10.17807/orbital.v7i4.72

Relaxometric Study Concerning the Action of A Complexant Agent on Petroleum

Applying a complexant agent to the contention and bioremediation of petroleum spills, although important for industry, is very rare. Therefore, the aim of this paper is to present a study concerning the influence of a complexant agent, namely chitosan, on petroleum using time-domain nuclear magnetic resonance (TD-NMR). Alterations in the transverse relaxation time (T2) values and peak areas were observed, inferring that the interaction of the complexant agent with petroleum causes destabilization, precipitation of chemical compounds and separation of phases (water and oil). Thus, a novel application involving this spectroscopic technique in the energy field is presented

Reação de Mannich: Metodologia Clássica na Formação de Ligação Carbono-Carbono

<p>A reação de Mannich é um método clássico para a preparação de b-aminocetonas e aldeídos, conhecidos como base de Mannich, sendo assim uma das reações mais importantes da química orgânica. Os adutos de Mannich possuem particular interesse devido às suas atividades biológicas, uso como intermediários sintéticos e precursores importantes de produtos farmacêuticos importantes. Nesse contexto, várias elegantes reações estereosseletivas de a-aminoalquilação foram desenvolvidas.</p

Relaxometric Study Concerning the Action of A Complexant Agent on Petroleum

Applying a complexant agent to the contention and bioremediation of petroleum spills, although important for industry, is very rare. Therefore, the aim of this paper is to present a study concerning the influence of a complexant agent, namely chitosan, on petroleum using time-domain nuclear magnetic resonance (TD-NMR). Alterations in the transverse relaxation time (T2) values and peak areas were observed, inferring that the interaction of the complexant agent with petroleum causes destabilization, precipitation of chemical compounds and separation of phases (water and oil). Thus, a novel application involving this spectroscopic technique in the energy field is presented

Stereochemistry of cyclopentane derivatives from (2,3)J(CH) dependence on dihedral angle (theta H-C-C-X)

The (2,3)J(CH) dependence on dihedral angle (theta H-C-C-X) for cyclopentane derivatives was investigated. We observed that the combined use of experimentally obtained (2,3)J(CH) values and the theoretically determined dihedral angles between the corresponding nuclei can be used to infer the relative stereochemistry of the ring substituents in cyclopentane derivatives. There is a good correlation between the magnitude of (3)J(CH) and the dihedral angle between the hydrogen and the coupled carbon (R-2 = 0.88). Copyright (C) 2008 John Wiley & Sons, Ltd