Investigation of the diastereoisomeric association complex for the separation of amino acid enantiomers on optically active stationary phases

Abstract

TFA-amino acid esters and TFA-dipeptide esters have been employed as optically active stationary phases for the resolution of amino acid enantiomers by gas chromatography. Structural consideration of the hydrogen bonded diastereoisomeric association complex formed during the separation of amino acid enantiomers led to the synthesis of an N-acyl-amino acid n-alkyl amide (N-caproyl-L-valine n-hexyl amide). This amino acid derivative fulfills the general requirements for the reversible association between the enantiomers and the asymmetric solvent molecules. The results obtained show that the amide portion, when in competition with the ester portion of a dipeptide phase, is involved in formation of the diastereoisometric association complex between the enantiomeric solutes and the chiral solvent by hydrogen bonds.