Evaluation of non-polar interactions in chiral recognition by alkylated β- and γ-cyclodextrin chiral stationary phases

Abstract

The gas chromatographic separation of enantiomers of seven N-TFA-O-alkyl amino acid derivatives was studied on four different permethyl- and 2,6-di-O-methyl-3-O-pentyl-β- and -γ-CD stationary phases.It was shown that the separation of enantiomers N-TFA-O-alkyl amino acid derivatives depends both on the length of the linear alkyl chain attached to the stereogenic carbon (R 1 ) and to the ester part of the amino acid derivative (R 2 ). The cyclodextrin cavity size also affected selectivity. The separation of the amino acid derivatives decreases with increasing length of both the R 1 and R 2 alkyl chains on β-CD stationary phases, but improves on γ-CD stationary phases. The separation of enantiomers of all N-TFA-O-methyl amino acid esters, is better on the larger γ-cyclodextrin CSPs except for enantiomers of N-TFA-O-alkyl esters of alanine which are better separated on β-CD stationary phases.