A study of carborane dipeptide stationary phases for the gas chromatographic resolution of amino acid enantiomers

N-Trifluoroacetyl (TFA) dipeptide-o-carboranyl propyl esters of L-valyl-L-valine and L-[alpha]-amino-n-butyryl-L-[alpha]-ainino-n-butyric acid have been prepared. The first step in the reaction sequences leading to these compounds involves the coupling of their tert-butyloxycarbonyl-L-amino acids with 1-hydroxypropyl-o-carborane. N,N'-carbonyldiimidazole was used as the coupling reagent. The properties of these dipeptides as stationary phases for the gas-liquid chromatographic separation of N-TFA-D,L-amino acid isopropyl esters have been examined. It was found that the amino acid derivatives have shorter retention times, while maintaining good separation factors, on the carborane phases as compared to other dipeptide stationary phases. Both high and low boiling derivatives have been resolved on a 400 ft capillary column in a reasonable amount of time. Additionally, the new phases have greater thermal stability.