Organic solutions of poly-γ-(benzyl-l-glutamate) (PBLG) generate a sufficient differential ordering effect (DOE) to discriminate enantiomers using proton decoupled carbon-13 NMR in natural abundance. Discrimination between enantiomers is observed through the carbon-13 chemical shift anisotropy (CSA) differences. This method is successfully applied to a large number of chiral molecules including a case of axial chirality and offers the advantage that no labeling or chemical modification of molecules is needed. In most cases, the chemical shift differences are large enough to measure the enantiomeric excess with accuracy. We show that this new tool is an attractive and powerful alternative to the existing enantiomeric analytical techniques.

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High-resolution, proton-coupled and decoupled, carbon-13 NMR in natural abundance is used to observe the spectra of enantiomers in chiral molecules dissolved in the poly(y-benzyl-L-glutamate) (PBLG)/CD,CI, liquidcrystalline system. Discrimination between enantiomers can be obtained either through differences in their dipolar interactions or in their chemical shift anisotropies. This technique provides a new tool for the visualization of enantiomers and the measurement of the enantiomeric ratio. Several specific examples are presented and discussed.

NMR spectroscopy of oriented samples makes accessible residual anisotropic intramolecular NMR interactions, such as chemical shift anisotropy (RCSA), dipolar coupling (RDC), and quadrupolar coupling (RQC), while preserving high spectral resolution. In addition, in a chiral aligned environment, enantiomers of chiral molecules or enantiopic elements of prochiral compounds adopt different average orientations on the NMR timescale, and hence produce distinct NMR spectra or signals. NMR spectroscopy in chiral aligned media is a powerful analytical tool, and notably provides unique information on (pro)chirality analysis, natural isotopic fractionation, stereochemistry, as well as molecular conformation and configuration. Significant progress has been made in this area over the three last decades, particularly using polypeptide-based chiral liquid crystals (CLCs) made of organic solutions of helically chiral polymers (as PBLG) in organic solvents. This review presents an overview of NMR in polymeric LCs. In particular, we describe the theoretical tools and the major NMR methods that have been developed and applied to study (pro)chiral molecules dissolved in such oriented solvents. We also discuss the representative applications illustrating the analytical potential of this original NMR tool. This overview article is dedicated to thirty years of original contributions to the development of NMR spectroscopy in polypeptide-based chiral liquid crystals.

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Ytterbium and lutetium ionic complexes derived from enantiopure substituted (R)-binaphthylamine ligands, of the general formula [Li(THF)n][Ln[(R)-C20H12(NR)2]2], have been investigated for the hydroamination/cyclization of several aminopentenes and an aminohexene. Complexes with isopropyl or cyclohexyl substituents on nitrogen atoms were found to be efficient catalysts under mild conditions for the formation of N-containing heterocycles with enantiomeric excesses up to 78%.

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. The stereochemical analysis of the product relied on (2)H NMR analysis in a chiral liquid-crystalline medium. It is concluded that the enzyme catalyses the fluorination with an inversion of configuration consistent with an S(N)2 reaction mechanism.