Gas and Liquid Chromatography On Chiral Stationary Phases: Thermodynamic Investigation and Bioanalysis.

Chirality, the phenomenon of optical activity, is extremely important in natural, living systems and therefore interactions with such systems are of interest. A large number of pharmaceuticals are chiral and since biological activity is often stereospecific it is important that the properties and toxicity of the individual enantiomers are properly evaluated. In order to study enantiomers, analytical methods are required that are capable of distinguishing between them. Resolution of enantiomers by chromatography can be achieved by reaction of the enantiomers with an optically pure single enantiomer of another compound to yield diastereoisomers. Alternatively a chiral environment can be created within the chromatographic system, by making one of the chromatographic phases chiral. Under such conditions the enantiomers can be separated via the formation of transient diastereoisomers as they pass through the system. The evaluation of some commercially available liquid cyclodextrin chiral stationary phases for capillary gas chromatography was performed with the separation of some chiral epoxide pharmaceutical intermediates. The mechanism responsible for the resolution of the enantiomers was investigated by determination of the thermodynamic parameters involved in the separation. The use of the columns for chiral separations of larger, more polar compounds was then considered. The use of chiral stationary phases for the bioanalysis of chiral compounds was also investigated. The analysis of p-trifluoromethylmandelic acid and a-methoxy-a-j (trifluoromethyl)phenylacetic acid in urine was achieved using the cyclodextrin GC phases following derivatisation of the compounds (formation of methyl esters). A HPLC method for a-methoxy-a-(trifluoromethyl)phenylacetic acid was also developed. Determination of enantiomer levels in the urine of rats dosed with the compounds revealed that a-methoxy-a-(trifluoromethyl)phenylacetic acid enantiomers were excreted unchanged, while racemic p-trifluoromethylmandelic acid underwent a unidirectional enantiomeric interconversion