The partial filling technique (PFT) in capillary electrophoresis (CE) is an efficient system where, only 50-800 nanolitres ofa chiral selector solution needs to be added to each run. PFT is especially applicable when these additives to the background electrolyte (BGE) are expensive or absorb UV light. The selector dissolved in the BGE is applied to the capillary as a plug, shorter than the effective length of the capillary, prior to application of the analyte. During the run both ends of the capillary are connected to the BGE. The applied plug and the analyte may move in opposite directions or in the same direction at different velocities depending on their electrophoretic mobilities. Thus the final plug length is either longer or shorter than the original length. The technique has been successfully applied in a number of studies including enantiomeric separation with a variety of selectors, and for the determination of conditional association constants.

The enantiomers of prilocaine were successfully resolved with alpha-cyclodextrin, and those of mepivacaine and bupivacaine, with methyl-beta-cyclodextrin as chiral selectors, by means of capillary zone electrophoresis (CZE) employing a partial filling technique. By this separation mode, a discontinous separation zone is formed in the capillary. Prior to application of the actual drug substance, the capillary is partially filled with the separation solution. During the enantioseparation both ends of the capillary are dipped into the running buffer solution, i.e., without chiral selector. The consumption of chiral selector is thus very low, less than a microliter per run. The repeatibility of the electrophoretic mobility of the enantiomers was better than 1.2% relative standard deviation (RSD). The effect of the length of the separation zone on the resolution of the enantiomers was studied. The application time of the chiral selector, instead of the selector concentration, was varied in order to improve and regulate the enantioresolution and reduce consumption of the chiral selector as much as possible. It was found that the enantioseparations were directly affected by the length of the separation zone, and there was a minimal plug length where complete enantioresolution was achieved.

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The formation of cytochrome P-450 metabolic intermediary (MI) complexes from the enantiomers of four 2-alkyl-substituted 1-phenyl-2-aminoethanes was investigated during reduced nicotinamide adenine dinucleotide phosphate (NADPH) dependent metabolism in liver microsomes from phenobarbital-pretreated rats. The 2-alkyl substituents were methyl (amphetamine), ethyl, n-propyl, and n-butyl groups. The chiral amines were prepared from the corresponding alkyl benzyl ketones by asymmetric hydrogenolytic transamination. Circular dichroism analysis showed that all the amines possessed the S-(+) and R-(-) configuration. The maximal velocity (Vmax(obsd) ) of complex formation increased with increasing size of the alkyl group, and for each series of enantiomers a good correlation was obtained between log Vmax(obsd) and the logarithm of the octanol/buffer partition coefficient of the substrates. With increasing lipophilicity, the S-(+) enantiomers became more active than the R-(-) isomers in generating the complex. The rates of complex formation for the faster S-(+) enantiomers coincided with those of the previously investigated racemates, indicating that the R-(-) enantiomers do not act as competitive enzyme inhibitors in the rat liver preparations. In agreement with two previous studies, the results from the present investigation establish a stereoselectivity in cytochrome P-450 MI complex formation by 1-phenyl-2-aminoethanes. However, detection of such differences are dependent on the intrinsic activity of the compound.

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