Separation of amino acid enantiomers by gas chromatography with an optically active stationary phase (N-TFA-L-valyl-L-leucine cyclohexyl ester)

Abstract

The resolution of amino acid enantiomers by gas chromatography on optically active stationary phases has been explained by the formation of hydrogen bonded diastereomeric association complexes. Structural considerations involving these complexes have led to the synthesis of a new phase, TFA-L-valyl-L-leucine cyclohexyl ester. Relative retention times and resolution factors have been determined for each enantiomeric pair of eleven amino acids and glycine. Investigations have uncovered some trends in resolution factors and relative retention times for amino acids on different dipeptide phases. These patterns led to an explanation for the difficulties found in resolving D, L-proline. Structural differences about the α-carbon in the dipeptide phase influence the elution pattern of TFA-amino acid isopropyl esters from the column. Particularly strong effects are found in the elution patterns of hydroxy amino acids on different dipeptide phases.