The use of exchangeable nuclei to observe enantiomers through deuterium NMR in chiral liquid crystalline solvents.

It is demonstrated that (2)H NMR in chiral liquid crystalline solvents can be used to measure enantiomeric excesses using exchangeable deuterons in alcohols. This is performed in a trivial way at low temperature (260-270 K) where a slow exchange regime was reached. Among the various alcohols used to explore the possibilities of this technique, an unusually large isotopic effect on molecular orientation between two isotopomers has been observed.

Spin-spin coupling edition in chiral liquid crystal NMR solvent.

The application of the G-SERFph pulse sequence is presented on enantiomeric mixtures dissolved in a chiral liquid crystal. It aims at editing, within one single 2D spectrum, every proton coupling which is experienced by a given proton site in the molecule, and leads to real phased T-edited spectroscopy (T=J+2D). This NMR experiment is based on the combination of homonuclear semi-selective refocusing techniques with a spatial frequency encoding of the sample.

Application of a (1)H delta-resolved 2D NMR experiment to the visualization of enantiomers in chiral environment, using sample spatial encoding and selective echoes.

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.

Empirical determination of the absolute configuration of small chiral molecules using natural abundance 2H NMR in chiral liquid crystals.

Natural abundance deuterium 2D NMR spectroscopy in polypeptide liquid crystals is used for empirically determining the absolute configuration of small chiral molecules.

Simplification of the 1H NMR spectra of enantiomers dissolved in chiral liquid crystals, combining variable angle sample spinning and selective refocusing experiments.

This work presents a technique to simplify overcrowded proton spectra in chiral liquid crystal solvents using rotation of the sample near the magic angle, VASS, combined with homonuclear selective refocusing 2D NMR experiments, SERF. This methodology provides a powerful tool to visualise enantiomers out of unresolved proton spectra. A modified SERF sequence is presented where the resulting 2D spectrum can be phased to increase the resolution.

Modified z-gradient filtering as a mean to obtain phased deuterium autocorrelation 2D NMR spectra in oriented solvents.

We describe a modified z-gradient filter scheme specifically designed to obtain pure absorption mode deuterium 2D NMR spectra recorded in oriented solvents. The proposed technique is investigated by analysing the evolution of the density operator for a spin I=1. The method is applied to the recently designed Q-COSY and Q-resolved 2D experiments to simplify the analysis of chiral molecules dissolved in weakly orienting chiral liquid crystals.

Analysis of the 13C NMR spectra of molecules, chiral by isotopic substitution, dissolved in a chiral oriented environment: towards the absolute assignment of the pro-R/pro-S character of enantiotopic ligands in prochiral molecules.

We examined and discuss the proton- and deuterium-decoupled carbon-13 1D spectrum of a molecule, chiral by virtue of the isotopic substitution, dissolved in a chiral oriented medium which simultaneously exhibits chiral discrimination, enantiomeric enrichment and isotope effect. Using the 1-deutero-(2',3',4',5',6'-pentadeuterophenyl)phenylmethanol orientationally ordered in a chiral nematic liquid crystal as illustrative example, we point out three important features. First, we demonstrate that the absolute assignment of the pro-R/pro-S character may be derived from the absolute configuration of the isotopically chiral analogue.

Heteronuclear selective refocusing 2D NMR experiments for the spectral analysis of enantiomers in chiral oriented solvents.

We report the use of carbon-proton heteronuclear selective refocusing 2D NMR experiments dedicated to the spectral analysis of enantiomers dissolved in weakly ordering chiral liquid crystalline solvents. The method permits the extraction of carbon-proton residual dipolar couplings for each enantiomer from a complex or unresolved proton-coupled 13C spectral patterns. Illustrative examples are analysed and discussed.

Enzymatic fluorination in Streptomyces cattleya takes place with an inversion of configuration consistent with an SN2 reaction mechanism.

The stereochemical course of the recently isolated fluorination enzyme from Streptomyces cattleya has been evaluated. The enzyme mediates a reaction between the fluoride ion and S- adenosyl-L-methionine (SAM) to generate 5'-fluoro-5'-deoxyadenosine (5'-FDA). Preparation of (5'R)-[5-(2)H(1)]-ATP generated (5'R)-[5-(2)H(1)]-5'-FDA in a coupled enzyme assay involving SAM synthase and the fluorinase.

Weakly oriented liquid-crystal NMR solvents as a general tool to determine relative configurations.

A new NMR method to determine the relative configuration of asymmetric centres is presented. It proceeds through the use of a weakly ordered solvent and the measurement of orientational order parameters. The method is illustrated by using dihydropyridone derivatives for which the orientations and the relative configurations of the asymmetric carbon atoms are determined unambiguously.

Natural abundance deuterium NMR spectroscopy in polypeptide liquid crystals as a new and incisive means for the enantiodifferentiation of chiral hydrocarbons.

Polymeric chiral liquid-crystalline solvents based on homopolypeptides are of interest with the view to discriminate between enantiomeric pairs of chiral hydrocarbons using proton-decoupled deuterium one- and two-dimensional NMR spectroscopy at natural abundance level. This method offers the major advantage that neither chemical modification nor isotopic labelling of the solutes to be studied is required. Chiral differentiation between optical isomers is observed through a difference in residual deuterium quadrupolar splittings.

Assay for the enantiomeric analysis of [2H1]-fluoroacetic acid: insight into the stereochemical course of fluorination during fluorometabolite biosynthesis in streptomyces cattleya.

A sensitive method for the configurational analysis of (R)- and (S)-[2H1]-fluoroacetate has been developed using 2H[1H]-NMR in a chiral liquid crystalline solvent. This has enabled biosynthetic experiments to be conducted which reveal stereochemical details on biological fluorination occurring during the biosynthesis of fluoroacetate and 4-fluorothreonine in the bacterium Streptomyces cattleya. In particular, feeding experiments to S.

Monitoring the differential ordering of enantiomers included into cyclodextrins through deuterium NMR in lyotropic liquid crystals.

Deuterium NMR in an aqueous non-chiral liquid crystal allows the discrimination of enantiomers through their ordering inside beta-cyclodextrins.

Enantiomeric and enantiotopic analysis of cone-shaped compounds with C(3) and C(3)(v) symmetry using NMR spectroscopy in chiral anisotropic solvents.

We describe the enantiomeric and enantiotopic analysis of the NMR spectra of compounds derived from the functionalized cone-shaped core, cyclotriveratrylenes (CTV), dissolved in weakly oriented lyotropic chiral liquid crystals (CLCs) based on organic solutions of poly-gamma-benzyl-L-glutamate. The CTV core lacks prostereogenic as well as stereogenic tetrahedral centers. However, depending on the pattern of substitution, chiral and achiral compounds with different symmetries can be obtained.

Extreme enantiomeric discrimination of fluoroalkanes using deuterium NMR in chiral liquid crystalline media.

The enantiomeric assay of fluoroalkanes using 2H-NMR in a chiral liquid crystalline medium is demonstrated, and at its limit the enantiomers of [5-(2)H]-5-fluorodecane were successfully resolved.