Chiral reagents for the determination of enantiomeric excess and absolute configuration using NMR spectroscopy

Abstract

Recent advances in the development of chiral derivatizing and solvating agents that facilitate the determination of enantiomeric excess and absolute configuration are reviewed. These include metal-containing species, host-guest systems, donor-acceptor compounds, and liquid crystal discriminating agents. In the aggregate, these reagents can be used to analyze a wide range of compound classes.

Matrix-assisted diffusion-ordered spectroscopy

“…The use of cyclodextrins has also been demonstrated to separate a number of catechin-like compounds typically found in green tea, and also in concentrated samples of green tea extract where individual catechins were resolved and identified 76 . Crown ethers are simpler cyclic oligomers, made up of repeating ether units, and also have a long record in enantioselectivity 77,78 and have been used in the mobile phase in some chromatography applications [79][80][81][82][83][84] . Among the compounds resolved in DOSY experiments using crown ethers as a matrix were structural isomers of substituted anilines, a phenol and an aniline and the R and S isomers of 2-methylpiperidine, although only some of the peaks were sufficiently well resolved in the chemical shift dimension to allow resolution of the diffusion coefficients 85 .…”

New Trends in Hexacoordinated Phosphorus Chemistry

“…In the last decades, NMR has evolved as one of the methods of choice for the measurement of the enantiomeric purity of chiral species [110,111].Anionic substances have an advantage over neutral reagents to behave as NMR chiral shift agents for chiral cations. They can form diastereomeric contact pairs directly and the short-range interactions that result can lead to clear differences in the NMR spectra of the diastereomeric salts.…”

Comparative Studies on Enantiomer Resolution of α-Amino Acids and Their Esters Using (18-Crown-6)-tetracarboxylic acid as a Chiral Crown Ether Selector by NMR Spectroscopy and High-Performance Liquid Chromatography

“…In order to determine the enantiomeric compositions of amino acids and their esters, generally, the NMR technique using 18-C-6-TA as a chiral solvating agent shows lower precision and accuracy than HPLC technique using chiral columns. 19 However, because of the simplicity of NMR-based analytical processes using a chiral solvating agent, this NMR analytical method may be practically useful for determinations of the enantiomeric purities of chiral analytes like α-amino acids and their esters.…”