Achiral Separation Research Articles

Simultaneous separation and enantioresolution of racemic local anesthetic drugs by capillary zone electrophoresis with Tween 20 and methyl-beta-cyclodextrin as selectors, employing a double plug technique.

A new approach for simultaneous chiral and achiral separations by capillary zone electrophoresis is described. Two adjacent selector plugs, consisting of Tween 20 as an achiral and methyl-beta-cyclodextrin (CD) as a chiral selector, are employed and four related local anesthetics are used as model compounds. The principles of the partial filling technique, whereby the capillary is filled with the chiral selector solution followed by the micellar solution at different plug lengths and concentrations, prior to application of the solutes, was employed. During the run both capillary ends were dipped in a simple buffer, i.e., one without additives. The two separation media worked independently without any interaction. Separation of the solutes and their enantiomers was regulated by adjusting both the concentration and plug length (PL) of the micellar solution in the capillary, employing methyl beta-CD as chiral selector either at 38 or 76 mM. The solutes were separated on the basis of their affinity towards the micellar phase before they reached the methyl-beta-CD plug for enantioseparation. In the absence of the micellar plug, the enantiomers of prilocaine overlapped those of bupivacaine. The solutes and their enantiomers were completely separated by employing two adjacent plugs consisting of 100 mM Tween 20 solution (PL approximately 10 cm) and methyl-beta-CD solution at either 38 or 76 mM (PL approximately 30 cm).

Investigation of the stereoselective metabolism of praziquantel after incubation with rat liver microsomes by capillary electrophoresis and liquid chromatography–mass spectrometry

Two different separation methods for the antischistosomal drug praziquantel and its metabolites by capillary electrophoresis are described. Achiral separation was obtained by micellar electrokinetic capillary chromatography using sodium dodecyl sulfate as micelle-forming surfactant. On the other hand, the negatively charged sulfobutylether-β-cyclodextrin as a chiral selector enabled the separation of the drug and its metabolites as well as their enantioseparation. Based on this separation, the enantioselectivity of the metabolism of praziquantel was studied by incubation of the drug with rat liver microsomes. Whereas trans- and cis-4-hydroxypraziquantel were mainly formed from the R-(−)-enantiomer, another, different monohydroxylated metabolite was only formed from the S-(+)-enantiomer. Information about the structure of these metabolites was obtained, using LC–MS.

HPLC Separation of the ZZ, ZE, EZ, and EE Geometric Isomers and EE Isomer Enantiomers of a Substituted Pentadienyl Carboxamide Using Achiral/Chiral Column Switching

Abstract The four geometric isomers of a substituted pentadienyl carboxamide were separated on an achiral aminopropyl column coupled with a silica precolumn. The R and S enantiomers of the biologically active EE isomer (RO 24–0238 and RO 24–2099) were resolved (Rs 1.65) on a cellulose-based chiral stationary phase (Chiracel OF). The coupled silica and aminopropyl columns were connected to the Chiralcel OF column through a six port switching valve that enabled transfer to the EE isomer to the chiral phase for enantiomer resolution. By examining the selectivity for separation of the geometric isomers of various achiral stationary phases using hexane-isopropanol mobile phases, a method was developed which linked the achiral separation of the geometric isomers with the chiral separation of the EE enantiomers.

Effect of temperature on chiral and achiral separations of diacylglycerol derivatives by high-performance liquid chromatography on a chiral stationary phase

Enantiomer separation of 1,2-diacyl- rac-glycerols (1,2- rac-DGs) as their 3,5-dinitrophenylurethane derivatives by high-performance liquid chromatography was carried out on a Sumichiral OA-4100 column. The separation of 1,2-DG enantiomers was improved by lowering the temperature. Linear relationships were found between the logarithm of the separation factor and the reciprocal of absolute temperature. Using thermodynamic concepts, detailed considerations are presented for the enantiomer separation and separation of molecular species differing in carbon number or olefinic bond number. Separation by carbon number is controlled by entropy differences, whereas separation by double bond number is based on enthalpy contributions.