Enantiodiscrimination Using a Chiral Crown Ether as a Chiral Solvating Agent Using NMR Spectroscopy

For enantiomer separation of a variety of chiral compounds, a number of chiral selectors have been developed and applied. Among these chiral selectors are chiral crown ethers, a class of synthetic polyether molecules that bind protonated chiral primary amines with high selectivity. This article focuses on enantiodiscrimination using (18-crown-6)-2,3,11,12-tetracarboxylic acid as a crown ether-type chiral solvating agent for nuclear magnetic resonance spectroscopic method in several chirotechnologies.

Application of an (18-Crown-6)-2,3,11,12-Tetracarboxylic Acid-Based Chiral Stationary Phase in Capillary Electrochromatography

Capillary electrochromatography is employed for the enantioseparation of α-amino acids and their derivatives. The synthesis and application of a covalently bonded chiral stationary phase containing (-)-(18-crown-6)-2,3,11,12-tetracarboxylic acid as chiral selector is described. Enantioseparations are performed using methanol/Tris-citric acid (20 mM, pH 3.0-4.5) (20:80, v/v) as mobile phase.

Differentiation of enantiomers by capillary electrophoresis

Capillary electrophoresis (CE) has matured to one of the major liquid phase enantiodifferentiation techniques since the first report in 1985. This can be primarily attributed to the flexibility as well as the various modes available including electrokinetic chromatography (EKC), micellar electrokinetic chromatography (MEKC), and microemulsion electrokinetic chromatography (MEEKC). In contrast to chromatographic techniques, the chiral selector is mobile in the background electrolyte. Furthermore, a large variety of chiral selectors are available that can be easily combined in the same separation system. In addition, the migration order of the enantiomers can be adjusted by a number of approaches. In CE enantiodifferentiations the separation principle is comparable to chromatography while the principle of the movement of the analytes in the capillary is based on electrophoretic phenomena. The present chapter will focus on mechanistic aspects of CE enantioseparations including enantiomer migration order and the current understanding of selector-selectand structures. Selected examples of the basic enantioseparation modes EKC, MEKC, and MEEKC will be discussed.

Enantioseparation of baclofen with highly sulfated β-cyclodextrin by capillary electrophoresis with laser-induced fluorescence detection

The enantioseparation of baclofen (4-amino-3-p-chlorophenylbutyric acid) was achieved by CE-LIF with highly sulfated beta-CD (HS-beta-CD) as chiral selector. Naphthalene-2,3-dicarboxaldehyde was used for the derivatization of nonfluorescent baclofen. HS-beta-CD (2%) containing 50 mM borate buffer at pH 9.5 was chosen as the optimal running electrolyte and applied to the analysis of baclofen enantiomers in human plasma. The linearity of calibration curves (R2 > or = 0.998) for R-(-) and S-(+)-baclofen was in the 0.1-2.0 microM concentration range. After a simple ACN-protein precipitation, the LOD of baclofen in plasma sample was found as low as 50 nM.