Probing the correlation between ligand efficacy and conformational diversity at the α1A-adrenoreceptor reveals allosteric coupling of its microswitches.

G protein-coupled receptors (GPCRs) use a series of conserved microswitches to transmit signals across the cell membrane via an allosteric network encompassing the ligand-binding site and the G protein-binding site. Crystal structures of GPCRs provide snapshots of their inactive and active states, but poorly describe the conformational dynamics of the allosteric network that underlies GPCR activation. Here, we analyzed the correlation between ligand binding and receptor conformation of the α1A-adrenoreceptor, a GPCR that stimulates smooth muscle contraction in response to binding noradrenaline. NMR of [13CϵH3]methionine-labeled α1A-adrenoreceptor variants, each exhibiting differing signaling capacities, revealed how different classes of ligands modulate the conformational equilibria of this receptor. [13CϵH3]Methionine residues near the microswitches exhibited distinct states that correlated with ligand efficacies, supporting a conformational selection mechanism. We propose that allosteric coupling among the microswitches controls the conformation of the α1A-adrenoreceptor and underlies the mechanism of ligand modulation of GPCR signaling in cells.

Strong hyperconjugative interactions limit solvent and substituent influence on conformational equilibrium: the case of cis-2-halocyclohexylamines.

The presence of strong stereoelectronic interactions involving the substituents in cis-2-substituted cyclohexanes may lead to results different from those expected. In this work, we studied the conformational behavior of cis-2-fluoro- (F), cis-2-chloro- (Cl), cis-2-bromo- (Br) and cis-2-iodocyclohexylamine (I) by dynamic NMR and theoretical calculations. The experimental data pointed to an equilibrium strongly shifted toward the ea conformer (equatorial amine group and axial halogen), with populations greater than 90% for F, Cl and Br in both dichloromethane-d 2 and methanol-d 4. Theoretical calculations (M06-2X/6-311++G(2df,2p)) were in agreement with the experimental, with no influence of the solvent or the halogen on the equilibrium. A principal component analysis of natural bond orbital energies pointed to the σ*C-X and σC-H orbitals and the halogen lone pairs (LPX) as the most significant for the hyperconjugative interactions that influenced the equilibrium. The σC-H → σ*C-X hyperconjugation and the interactions involving the LPX counterbalance each other, explaining the non-influence of the halogen on the conformational equilibrium. These interactions are responsible for the strong preference for the ea conformer in cis-2-halocyclohexylamines, being strong enough to restrain the shift in the equilibrium due to other factors such as steric repulsion or solvent effects.

Experimental and theoretical insights in the alkene-arene intramolecular π-stacking interaction.

Chiral acrylic esters derived from biomass were developed as models to have a better insight in the aryl-vinyl π-stacking interactions. Quantum chemical calculations, NMR studies and experimental evidences demonstrated the presence of equilibriums of at least four different conformations: π-stacked and face-to-edge, each of them in an s-cis/s-trans conformation. The results show that the stabilization produced by the π-π interaction makes the π-stacked conformation predominant in solution and this stabilization is slightly affected by the electron density of the aromatic counterpart.

Structural, conformational and vibrational properties of 1,1,1-Trifluoro-N-(1,1,2,2,2-pentafluoroethyl) methanesulfinimidoyl chloride, CF3CF2-N=S(Cl)CF3.

The structural, conformational, and configurational properties of 1,1,1-Trifluoro-N-(1,1,2,2,2-pentafluoroethyl) methanesulfinimidoyl chloride, CF3CF2NS(Cl)CF3 have been studied by vibrational spectroscopy [IR (vapor) and Raman (liquid)] and quantum chemical calculations [B3LYP, MP2 and B3PW91 levels of theory using the 6-311+G(d), 6-311+G(df) and 6-311+G(2df) basis sets]. According to these theoretical approximations, CF3CF2-N=S(Cl)CF3 exists in the gas phase as a mixture of a favored anticlinal form (CN bond anticlinal with respect to the CSCl bisector) with C1 symmetry and a less abundant syn conformer showing C1 symmetry as well (ΔG° ≈ 1.20 kcal mol(-1)). Due to the small contribution only a few corresponding vibrational modes of the syn conformer could be assigned confidently in the experimental spectra. Compared to CF3CF2-N=S(F)CF3, the replacement of F by Cl produces a clear change in NS bond length and the corresponding stretching frequency, without affecting the conformational properties.

CF3CF2N=S(F)CF3: vibrational spectra and conformational properties.

The structural, conformational, and configurational properties of 1,1,1-trifluoro-N-(1,1,2,2,2-pentafluoroethyl) methanesulfinimidoyl fluoride, CF3CF2N=S(F)CF3 have been studied by vibrational spectroscopy [IR (vapor) and Raman (liquid)] and quantum chemical calculations [B3LYP, MP2 and B3PW91 levels of theory (using the 6-311+G(d) and 6-311+G(2df) basis sets). According to these theoretical approximations, CF3CF2N=S(F)CF3 might be found in the gas phase as a mixture of a favoured anticlinal form (C-N bond anticlinal with respect to the C-S-F bisector angle) and a less abundant syn conformer showing C1 symmetry as well (ΔG°≈1.5 kcal mol(-1)). However, corresponding vibrational modes for these conformers show only small shifts which would not allow confidently detecting the rather small contribution of this second form in the experimental spectra.

Estudo e determinação teórica de propriedades físico-químicas de fármacos anti-hipertensivos inibidores da Enzima Conversora de Angiotensina / Theoretical study and determination of physicochemical properties of antihypertensive angiotensin-converting enzyme inhibitors

O pacote de softwares SpartanTM vs 04 foi utilizado para calcular algumas propriedades físico-químicas de uma série de inibidores da Enzima Conversora de Angiotensinogênio ECA. Simultaneamente, o pacote MarvinSketch 5.0.0 foi empregado para calcular o Coeficiente de Partição P dos inibidores. Através da análise dos resultados, conclui-se que: a) o arranjo termodinâmico mais estável desses inibidores mimetiza aquele dos resíduos pré-terminais da angiotensina II, b) há grande similaridade entre as cargas dos átomos que se ligam à macromolécula e c) os cálculos mostram diferenças significativas entre os valores de P para os inibidores. Portanto, as diferenças farmacológicas existentes entre os inibidores estão mais intimamente relacionadas ao coeficiente de partição do que à capacidade destes de inibir o sítio ativo da ECA.

The software package SpartanTM 4.0 was employed to calculate some physicochemical properties of a series of available ACE inhibitors. Simultaneously, the program MarvinSketch 5.0.0 was employed to calculate the partition coefficients (P) of the same compounds. After analyzing the results, we conclude that: a) from a thermodynamic point of view, the most stable conformer of each inhibitor resembles, as expected, the most stable spatial arrangement of the preterminal residues of angiotensin II; b) there is great similarity among the charge profiles of the potential binding sites of all the inhibitors; c) there are large differences in P among these compounds. Summing up, the pharmacological differences reported between the inhibitors are more closely linked to their lipophilic properties than to their capacity to block the ACE active center.