Cyclodextrins as Dominant Chiral Selective Agents in the Capillary Separation Techniques

Abstract

This review paper shows the dominant role of the cyclodextrins in the chiral separations using capillary columns (GC, SFC, CE). The cyclodextrins (CDs) have extremely broad chiral selectivity spectra because they have several different chiral recognition sites in various arrangements and various interaction modes. Their chiral selectivity features can further improve with their various substitutions. Their selectivities are moderate therefore they need high efficiency separations (capillary columns) for good chiral resolutions. The shape selectivity of cyclodextrins is also shown with non-chiral isomers too. The utility of the cyclodextrins is demonstrated with several examples based on the personal observations of authors and critical review of literature. The theoretical backgrounds of their chiral recognitions (e.g. H-bond interaction, inclusion, induced fit) are discussed in depth. This paper is not application oriented but is dealing with mostly on the physical and chemical background of separations using CDs.

Silylated-Acetylated Cyclodextrins as Chiral Sensors for the Enantiodiscrimination of Fluorinated Anesthetics

“…Thanks to their chirality, derivatized and native cyclodextrins can give rise to stereoselective recognition phenomena, which can be exploited in asymmetric syntheses [ 4 , 5 ] in order to design chromatographic separation systems [ 6 , 7 , 8 , 9 , 10 ] or as chiral solvating agents (CSAs) for nuclear magnetic resonance (NMR) spectroscopy [ 4 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 ].…”

Structure–Chiral Selectivity Relationships of Various Mandelic Acid Derivatives on Octakis 2,3-di-O-acetyl-6-O-tert-butyldimethylsilyl-gamma-cyclodextrin Containing Gas Chromatographic Stationary

“…The chiral recognition depends on the ratio of the interaction energies between the members of an enantiomer. Even an only 0.014 kcal/mol interaction difference (α = 1.02) is enough for the baseline separations of the enantiomers using very efficient chromatographic techniques (GC and CE) [8].…”

“…The most widely used chiral selectors are cyclodextrins in gas chromatography and capillary electrophoresis practices [3,5,8]. Cyclodextrins (CDs) are cyclic oligosaccharide molecules, which contain six, seven, or eight D(+)-glucopyranose units, assigned with the Greek letters α, β, and γ, respectively [9].…”

“…The CDs can encapsulate suitable substances in their apolar cavities, forming noncovalent host-guest inclusion complexes. The CDs have extremely broad chiral recognition spectra for the following reasons [8]:…”

Hydrolysis and Enantiodiscrimination of (R)- and (S)-Oxazepam Hemisuccinate by Methylated β-Cyclodextrins: An NMR Investigation

“…As a matter of fact, interaction at the apolar cavity of cyclodextrins constitutes a privileged interaction mechanism with several kinds of substrates leading to the inclusion of their apolar moieties [14][15][16][17][18]. Moreover, being cyclodextrins chiral, the formation of diastereomeric inclusion complexes produces potentially differentiable signals for the two included enantiomers by chromatographic [19][20][21][22][23][24][25] and/or spectroscopic techniques [24][25][26][27][28]. Commonly, inclusion does not involve polar pendants of enantiomeric substrates which may protrude from the large and small rims of the cyclodextrins and interact with cyclodextrin hydroxyl functions incurring into hydrolytic processes, which have been reported for ester compounds [29][30][31].…”