Gas Chromatographic Separation of Enantiomers on Cyclodextrin Derivatives

Abstract

In investigations concerned with the phenomenon of molecular chirality, the use of gas chromatography for the enantiomeric analysis of stable, volatile compounds is a technique of steadily growing importance. ['] In the last three years an important breakthrough in gas-chromatographic separation of enantiomers has been achieved by using alkylated cyclodextrins (a, p, and y) as chiral stationary phases in high-resolution capillary columns. In academic and commercial practice two different and complementary strategies have been adopted up to now. In the first, alkylated cyclodextrins are diluted with polysiloxanes and coated on glass or fused silica capillary columns. In the second, lipophilic per-n-pentylcyclodextrins and hydrophilic di-n-pentyl-and hydroxyalkylpermethylcyclodextrins are coated directly in the form of liquid phases onto suitably pretreated glass or fused silica surfaces. These techniques permit enantiomer separations not only for polar diols and alcohols, derivatized hydroxycarboxylic acids, amino acids, sugars, and alkyl halides, but also for nonpolar alkenes, cyclic saturated hydrocarbons, and metal 7~ complexes. An important aspect for practical applications is that in many cases the enantiomers can be separated without previous derivatization. Whereas the resolution of racemates of unfunctionalized hydrocarbons is attributed to an enantioselective hostguest inclusion complex, some observations indicate that for polar guest molecules additional enantioselective interactions are also involved. The new chiral stationary phases can be used over a wide range of temperatures (25 to 250 "C). The technique described is likely to become widely adopted as a simple, accurate and highly sensitive method for the enantiomeric analysis of chirdl compounds that can be vaporized without decomposition. It will also stimulate future research aimed at finding universal cyclodextrin phases and elucidating the mechanisms of enantioselectivity.

Contributions to the theory and practice of the chromatographic separation of enantiomers

“…The historical development is shown in Chart 1 (right). 59 Today, modified CDs are capable of separating almost any class of volatile chiral compounds by enantioselective GC. More than 20,000 entries on the use of alkylated/acylated cyclodextrins had been recorded in the Chirbase data collection by 2000.…”

“…10, bottom). 59 Chemically linking permethylated b-cyclodextrin to a poly(hydromethyl)siloxane backbone via platinum-catalyzed hydrosilylation to furnish Chirasil-b-Dex 9 (cf. Chart 3) was proposed previously 60 and subsequently carried out independently by Schurig et al 55 and Fischer et al 66 All three Chirasil-b-Dex regioisomers containing a mono-octamethylene spacer in the 2-, 3-, and 6-positions of one glucose moiety, respectively, have been prepared by elaborate functional group protection chemistry.…”

Chiral and Chirality Discrimination on Helical Polyacetylenes

“…[26][27][28][29][30] We have recently found that a novel optically active, stereoregular poly(phenylacetylene) derivative bearing a β-cyclodextrin residue as the side group (poly-25) exhibits a macromolecular helicity inversion accompanied by a color change responding to molecular and chiral recognition events that occurred at the remote side chain (Fig. 6).…”

Gas Chromatographic Analysis of Plant and Insect Surface Compounds: Cuticular Waxes and Terpenoids

“…The first GC separations of enantiomers using CDs were obtained by Koscielski & Sibilska in 1983; they separatedand -pinene, and the corresponding pinanes and δ-3-carene with a column packed with underivatized CDs. CDs are generally carried in non-polar to moderately polar polysiloxanes, as first proposed by Schurig & Novotny (1990). The main reasons for this are the wider range of operating temperatures, the inertness and efficiency of columns prepared by high temperature silylation, the possibilities of tuning column polarity by using different diluting phases, the small amounts of CD necessary to prepare columns, the shorter analysis times, and the possibility of measuring the thermodynamic parameters involved in enantiomer discrimination.…”