Visualization of enantiomers in a polypeptide liquid-crystal solvent through carbon-13 NMR spectroscopy

Lesot, Philippe; Merlet, Denis; Meddour, Abdelkrim; Courtieu, Jacques; Loewenstein, A.

doi:10.1039/ft9959101371

Cited by 62 publications

(98 citation statements)

References 6 publications

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“…For enantiodiscrimination, the best‐studied alignment medium is the liquid crystalline phase consisting of PBLG and chloroform. It was successfully applied for analyzing racemic mixtures or enantio‐enriched mixtures: The groups of Courtieu and Lesot discriminated enantiomers by natural abundance 13 C spectra, discussed the use of multinuclear NMR for enantiomeric differentiation, and assigned enantiotopic ligands in prochiral molecules using 13 C spectra . They introduced deuterium NMR in natural abundance as a means to enantiodifferentiate chiral hydrocarbons .…”

Section: Discussionmentioning

confidence: 99%

Chiral discrimination of amines by anisotropic NMR parameters using chiral polyacrylamide‐based gels

Schmidt

Sun

Leonov

et al. 2012

Magnetic Reson in Chemistry

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A new chiral alignment medium for dimethyl sulfoxide, methanol, and water as solvents was developed. Because both enantiomers of the gel are available, it is possible to enantiodiscriminate natural products such as strychnine HCl that naturally occurs as single enantiomer. With the two methods of achieving anisotropy, namely stretching and confinement, the degree of alignment can be adjusted, and the director changed from horizontal to vertical. This increases the applicability. Three compounds were enantiodiscriminated on the basis of residual dipolar coupling data: mefloquine HCl, strychnine HCl, and menthylamine HCl.

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Section: Discussionmentioning

confidence: 99%

Chiral discrimination of amines by anisotropic NMR parameters using chiral polyacrylamide‐based gels

Schmidt

Sun

Leonov

et al. 2012

Magnetic Reson in Chemistry

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“…The best results so far have been obtained using lyotropic liquid crystals made of organic solution of synthetic homo-polypeptides such as PBLG dissolved in chloroform for instance. [2,23,24] A liquid-crystalline NMR sample was prepared by diluting 39.6 mg of racemic mixture of (±)3-butyn-2-ol ( Fig. 3(b)) in a liquid-crystalline phase composed of 112 mg of PBLG and 798 mg of CDCl 3 , using standard procedure described elsewhere.…”

Section: Enantiomeric Discrimination In Pblgmentioning

confidence: 99%

Application of a ¹H δ‐resolved 2D NMR experiment to the visualization of enantiomers in chiral environment, using sample spatial encoding and selective echoes

Giraud

Joos

Courtieu

et al. 2009

Magnetic Reson in Chemistry

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We present the application of a 2D broadband homodecoupled proton NMR experiment to the visualization of enantiomers. In a chiral environment, the existence of diastereoisomeric intermolecular interactions can yield-generally slight-variations of proton chemical shifts from one enantiomer to another. We show that this approach, which relies on a spatial encoding of the NMR sample, is particularly well suited to the analysis of enantiomeric mixtures, since it allows, within one single 2D experiment, to detect subtle chemical shift differences between enantiomers, even in the presence of several couplings. This sequence, which uses semiselective radio-frequency (rf) pulses combined to a z-field gradient pulse, produces different selective echoes in various parts of the sample. The resulting homonuclear decoupling provides an original delta-resolved spectrum along the diagonal of the 2D map where it becomes possible to probe the chiral differentiation process through every proton site where the resulting variation in the chemical shift is detectable. We discuss the advantages and drawbacks of this approach, regarding other experiments which provide homodecoupled proton spectra. This methodology is applied to the observation of enantiomers of (1) ( +/- )2-methyl-isoborneol coordinated to europium (III) tris[3-(trifluoromethyl-hydroxymethylene)-(+)-camphorate] in isotropic solution, and (2) ( +/- )3-butyn-2-ol dissolved in a chiral liquid-crystal solvent, in order to show the robustness of this pulse sequence for a wide range of chiral samples.

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“…Finally, note that enantiomers of 1 have also been discriminated by proton-decoupled 13 C NMR spectroscopy. [14,36] Remarkably, this example illustrates that NMR spectroscopy in CLCs can be used to analyse chiral molecules without any stereogenic centre and devoid of conventional reactive functionality for which classical NMR tools are rather limited. [15] From a conformational analysis point of view, we show here that the interconversion between enantiomers of 1 is sufficiently slow on the 2 H NMR timescale to allow separation of their deuterium signals at room temperature.…”

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confidence: 99%

Analysis of Intramolecular Dynamic Processes in Enantiomeric Diaryl Atropisomers and Related Derivatives by ²H NMR Spectroscopy in Polypeptide Liquid Crystals

Lafon

Lesot

Fan

et al. 2007

Chemistry A European J

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We demonstrate the analytical potential of 2H-{1H} NMR spectroscopy in weakly ordering, chiral lyotropic liquid crystals made of poly(gamma-benzyl-L-glutamate) (PBLG) dissolved in chloroform or dichloromethane for investigating the intramolecular dynamic processes of four deuterated diaryls (derivatives of 1-(4'-methylphenyl)naphthalene). When the rotation of the aryl groups about the sp(2)--sp(2) bond is sufficiently slow relative to the NMR timescale, the method allows the spectral discrimination of enantiomeric atropisomers or enantiotopic directions in the prochiral derivatives. The effect of the position of substituents on the phenyl group on the conformational dynamics of these compounds has been examined as well as the nature of the organic co-solvent. When coalescence phenomena are observed, simulation of the experimental 2H-{1H} lineshapes using a formalism tailored for two deuterons undergoing mutual exchange allows the rate constants and the activation parameters for the internal rotation processes to be calculated. Experimental values of DeltaH(not equal) have been compared with data evaluated by molecular modelling calculations and the activation parameters are discussed for the various compounds. It is shown that these polypeptide mesophases have no significant impact on the interconversion dynamics of these compounds. In contrast with the nematic thermotropic phases, Haller's equation cannot be used to predict the evolution of the quadrupolar splittings (Deltanu(Q) values), and hence the order parameters, versus T in the PBLG mesophases. For these particular lyotropic systems, it is shown that an exponential function of the form Deltanu(Q)[Hz]=C x exp (-E/RT[K]) provides excellent agreement between the experimental and expected Deltanu(Q) values. Analysis of the results reported in this work suggests that orientation and chiral discrimination phenomena in these lyotropic solvents could be treated separately because they would involve different interaction mechanisms.

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Visualization of enantiomers in a polypeptide liquid-crystal solvent through carbon-13 NMR spectroscopy

Cited by 62 publications

References 6 publications

Chiral discrimination of amines by anisotropic NMR parameters using chiral polyacrylamide‐based gels

Chiral discrimination of amines by anisotropic NMR parameters using chiral polyacrylamide‐based gels

Application of a ¹H δ‐resolved 2D NMR experiment to the visualization of enantiomers in chiral environment, using sample spatial encoding and selective echoes

Analysis of Intramolecular Dynamic Processes in Enantiomeric Diaryl Atropisomers and Related Derivatives by ²H NMR Spectroscopy in Polypeptide Liquid Crystals

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Visualization of enantiomers in a polypeptide liquid-crystal solvent through carbon-13 NMR spectroscopy

Cited by 62 publications

References 6 publications

Chiral discrimination of amines by anisotropic NMR parameters using chiral polyacrylamide‐based gels

Chiral discrimination of amines by anisotropic NMR parameters using chiral polyacrylamide‐based gels

Application of a 1H δ‐resolved 2D NMR experiment to the visualization of enantiomers in chiral environment, using sample spatial encoding and selective echoes

Analysis of Intramolecular Dynamic Processes in Enantiomeric Diaryl Atropisomers and Related Derivatives by 2H NMR Spectroscopy in Polypeptide Liquid Crystals

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Application of a ¹H δ‐resolved 2D NMR experiment to the visualization of enantiomers in chiral environment, using sample spatial encoding and selective echoes

Analysis of Intramolecular Dynamic Processes in Enantiomeric Diaryl Atropisomers and Related Derivatives by ²H NMR Spectroscopy in Polypeptide Liquid Crystals