Comparison of enantioselective separation of N- tert.-butyloxycarbonyl amino acids and their non-blocked analogues on teicoplanin-based chiral stationary phase

Abstract

A teicoplanin-based chiral stationary phase (CSP) was tested for enantioseparation of underivatized amino acids and their N- tert.-butyloxycarbonyl ( t-Boc) derivatives, important precursors in peptide synthesis. Mobile phase composition was optimized for organic modifier and triethylamine acetate buffer (TEAA) contents, and retention and enantioresolution of t-Boc-amino acids and their non-blocked analogues were compared. The importance of the amino group of amino acids in the interaction mechanism was evaluated. Native amino acids have better possibility for interaction with teicoplanin; they are more retained on the CSP and better enantioresolved than the blocked amino acids. Presence of triethylamine in the aqueous portion of the mobile phase was shown to be important for separation of enantiomers of t-Boc-amino acids; while native amino acids were almost not affected by the addition of TEAA. Results obtained for blocked amino acid on teicoplanin CSP with mobile phase composed of 1% triethylamine acetate, pH 4.1 and organic modifier were compared to those got on hydroxypropyl-β-cyclodextrin CSP. Good enantioseparation in a reasonable analysis time was obtained on the teicoplanin-based chiral stationary phase.