Stereoselective analysis

Although the majority of chiral CEC—MS applications still involve packed columns, few reports on chiral OT-CEC-MS are found in recent literature. The feasibility of coupling OT-CEC (using a short Chirasil-Dex-coated capillary column) to MS and MS/MS for trace analysis of hexobarbital enantiomers in biological fluids was reported by Schurig and Mayer. More recently, Kamande et al. investigated polyelectrolyte multilayer (PEM) coating as a new medium for the separation of chiral analytes, and PEM-coated capillaries were successfully coupled to ESI/MS for the stereoselective analysis of five /1-blockers. 

Cherkaoui, S., Rudaz, S., Varesio, E., and Veuthey, J. L. (2001). On-line capillary electrophoresis-electrospray mass spectrometry for the stereoselective analysis of drugs and metabolites. Electrophoresis 22, 3308—3315. 

Rudaz, S., Veuthey, J. L., Desiderio, C., and Fanali, S. (1999). Simultaneous stereoselective analysis by capillary electrophoresis of tramadol enantiomers and their main phase I metabolites in urine.. Chromatogr. A 846, 227—237. 

S Rudaz, S Cherkaoui, P Dayer, S Fanali, J-L Veuthey. Simultaneous stereoselective analysis of tramadol and its main metabolites by on-line capillary zone electrophoresis-electrospray ionization mass spectrometry. J Chromatogr A 868 295-303, 2000. 

Coles R, Kharasch ED (2007) Stereoselective analysis of bupropion and hydroxybupropion in human plasma and urine by LC/MS/MS. J Chromatogr B Anal Technol Biomed Life Sci 857 67-75... 

Liu W, Wang F, Li HD (2007) Simultaneous stereoselective analysis of venlafaxine and O-desmethylvenlafaxine enantiomers in human plasma by HPLC-ESI/MS using a vancomycin chiral column. J Chromatogr B Anal Technol Biomed Life Sci 850 183-189... 

Methylthiohexanol and cis/trans-2-methy -4-pvopy -1,3-oxathiane have been reported by Winter et al. [71] to play important roles in the delicate flavour of the yellow passionfruit, in spite of their occurrence in the extreme trace levels. Using complexation GC, the stereoselective analysis of all the four stereoisomers of 2-methyl-4-propyl-l,3-oxathiane was achieved. This was the first direct stereochemical... 

Besides the routine stereoselective analysis, low cost and simplicity of CE and CEC methods make them popular tools for fast screening of chiral selectors [112], for studying mechanisms of discrimination, or for determining the binding constant, as it has been shown for t-BuCQN and (S)-DNB-leucine complex [113]. 

As Louis Pasteur proposed in his time, enantiomers can be separated as diastereomeric derivatives after a chemical reaction with a chiral selector using fractional recrystallization (see Chapter 5). However, separation techniques such as chromatography and electrophoresis are now recognized for fhe separation of enantiomers. Even if chromatography is considered as fhe method of choice for chiral analytical purposes (see Chapter 7), capillary electrophoresis (CE) has recently gained importance in fhe field of stereoselective analysis. 

It can be noted that the lack of sensitivity of CE for biological fluid concentrations remains the major bottleneck. However, coupling CE with mass spectrometry (MS) can overcome this drawback. These two analytical techniques are orthogonal and therefore their mutual complementarity is important. Hyphenation of CE with mass spectrometry appears appropriate for the stereoselective analysis of numerous compounds in various matrices. Moreover, the use of mass spectrometry in the selected ion monitoring mode results in very high selectivity, as well as improved sensitivity compared to conventional UV detection. 

Hayball, P.J. Tamblyn, J.G. Holden, Y Wrobel, J. Stereoselective analysis of ketorolac in human plasma by high-performance liquid chromatography. Chirality, 1993, 5, 31-35... 

Rumiantsev, D.O. Ivanova, T.V. Solid-phase extraction of Styrosorb cartridges as a sample pretreatment method in the stereoselective analysis of propranolol in human serum. J.Chromatogr.B, 1995, 674, 301-305... 

Clohs L., McErlane K.M., Comparison between capillary electrophoresis and high-performance liquid chromatography for the stereoselective analysis of carvedilol in serum. J. Pharm. Biomed. Anal., 31, 407-412(2003). 

Stereoselectivity analysis involved optimization of four transition states for the C-C bond formation step leading to different diastereomers (Figure 3.11). Computed selectivity (100% ee and 60 1 dr) correlated well with the experimental values (98% ee and >30 1 dr). 

S. Fuchs, Th. Beck, S. Burkardt, M. Sandvoss, and A. Mosandl, Biogenetic studies in Mentha x piperita. 1. Deuterium-labeled monoterpene ketones Synthesis and stereoselective analysis, J. Agiic. Food Chem. 47 3053 (1999). 

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