Conformational isomerism

About: Conformational isomerism is a research topic. Over the lifetime, 11563 publications have been published within this topic receiving 199312 citations.

Slow interconversion of enantiomeric conformers or atropisomers of anilide and urea derivatives of 2-substituted anilines

Abstract: N-Acylated 2-substituted anilines undergo slow Ar–N bond rotation, allowing in some cases isolation of enantiomeric or diastereoisomeric atropisomers and in others the determination of the rate of Ar–N bond rotation by NMR. 2-Iodoanilides bearing a branched N-substituent demonstrate sufficient enantiomeric stability to be resolvable, either by HPLC or by formation of diastereoisomeric lactanilide derivatives. For the first time, the rates of Ar–N rotation in 2-substituted N,N′-diarylureas have been established: they mainly fall in the region of 50–70 kJ mol−1 with a relatively weak dependence on substituent size.

The importance of conformational search: a test case on the catalytic cycle of the Suzuki–Miyaura cross-coupling

Abstract: Conformational diversity is an often neglected aspect in computational studies of transition metal complexes, even when relatively large systems are involved. The importance of conformational searches is illustrated through the analysis of the errors that could be caused by a wrong choice of conformers in the computational study of the Suzuki–Miyaura cross-coupling between CH2=CHBr and CH2=CHB(OH)2 catalyzed by [(PPh3)2Pd] or [(P(i-Pr)3)2Pd]. The error bars associated with conformational diversity of the [(PPh3)2Pd] catalyst range between 0.3 and 6.7 kcal/mol, the values growing up to 11.4 kcal/mol when the more flexible [(P(i-Pr)3)2Pd] catalyst is considered.

Studies of solvent effects on conformers of glycine molecule

Abstract: Conformational stability and solvent effects on selected conformers of glycine under different environment, such as polar and apolar solvents have been studied using ab initio and density functional theory (DFT) methods. The molecular geometries have been optimized using HF/6-31+G ∗ method of ab initio and B3LYP/6-31+G ∗ and B3PW91/6-31+G ∗ hybrid DFT methods. The effects of solvent on the geometrical parameters, relative stability and physical properties, such as dipole moment, etc. have been studied for the conformers of glycine.

Probing the Stereochemical Requirements for Receptor Recognition of δ Opioid Agonists through Topographic Modifications in Position 1

Abstract: A series of side-chain constrained tyrosine derivatives, 2‘,6‘-dimethyl-β-methyltyrosines (TMT), has been designed and incorporated into position 1 of the highly selective δ opioid agonists DPDPE (Tyr-d-Pen2-Gly-Phe-d-Pen5-OH) and deltorphin I (DELT I, Tyr-d-Ala-Phe-Asp-Val-Val-Gly-NH2). Molecular mechanics calculations on isolated TMT residues and nuclear magnetic resonance (NMR) studies of the TMT1-containing peptides in DMSO showed that each of the four stereoisomers of TMT favors one particular rotamer of the side-chain χ1 torsional angle. Therefore, substitution of four TMT isomers for Tyr1 allows us to perform a systematic conformational scan through three staggered rotamers of the aromatic side chain, gauche (−), trans, and gauche (+), and to explore specific binding requirements of the receptor in relation to the side chain conformation. The potency and selectivity of four isomers of [TMT1]DPDPE and four isomers of [TMT1]DELT I were evaluated by radioreceptor binding assays in the rat brain using ...

Ab initio comprehensive conformational analysis of 2'-deoxyuridine, the biologically significant DNA minor nucleoside, and reconstruction of its low-temperature matrix infrared spectrum.

Abstract: A comprehensive conformational analysis of isolated 2'-deoxyuridine (dU), a minor DNA nucleoside, has been performed by means of ab initio calculations at the MP2/6-311++G (d,p)//DFT B3LYP/6-31G (d,p) level of theory. At 298.15 and 420 K, all 94 allowed conformers of dU are within 8.96 and 7.91 kcal/mol Gibbs energy ranges, respectively. Syn orientation for the base and South (S) conformers for the sugar dominate at 298.15 K: syn/anti=62.3%:37.7% and S/N=77.2%:22.8%. At 420 K in the majority of conformers, the base is anti oriented and the population of North (N) sugars increases: syn/anti=39.3%:60.7% and S/N=63.0%:37.0%. Values of all conformational parameters and correlations between them, as well as their correlations with valence bonds, and also correlations between valence bonds and angles were estimated. In general, 14 types of intramolecular H-bonds were detected (1-3 H-bonds per conformer, the total number 175), namely, C1'H...O2 (16 H-bonds), C2'H1...O5' (9), C2'H2...O2 (21), C3'H...O2 (21), C5'H1...O2 (14), C5'H2...O2 (11), C6H...O4' (37), C6H...O5' (22), C3'H...HC6 (4), O5'H...HC6 (2), O3'H...O5' (5), O5'H...O4' (1), O5'H...O3' (4), and O5'H...O2 (8). Geometric, vibrational, structural-topological, and energetic features of the OH...O intramolecular H-bonds in dU conformers were determined. The close similarity between energetic and geometric characteristics of dU and thymidine DNA-like conformers in anti and relevant syn conformations and their transition states of the anti-->syn interconversion implies that mismatch DNA glycosylase discriminates between the two nucleosides, mainly because of the difference in the shapes of their bases. Convolution of calculated IR spectra of all the dU conformers within the limits 3400-3700 cm(-1) appears to be consistent with its low-temperature matrix IR spectrum (Ivanov et al. Spectrochim. Acta, Part A 2003, 59, 1959), wavenumber discrepancy not exceeding 1%. It was concluded that, for a reliable reproduction of the experimental spectrum, the whole set of conformers should be taken into consideration. The suggested method makes reconstruction of the isolated nucleoside IR spectrum at a physiological interval of temperature reasonably possible.