Enantiomeric separation of N‐protected amino acids by non‐aqueous capillary electrophoresis using quinine or Tert‐butyl carbamoylated quinine as chiral additive

Abstract

A capillary electrophoretic (CE) method for the enantioseparation of N-protected chiral amino acids was developed using quinine and tert-butyl carbamoylated quinine as chiral selectors added to nonaqueous electrolyte solutions (NACE). A series of various N-derivatized amino acids were tested as chiral selectands, and in order to optimize the CE enantioseparation of these compounds, different parameters were investigated: the nature of the organic solvent, the combination of different solvents, the nature and the concentration of the background electrolyte, the selector concentration, the capillary temperature, and the applied voltage. The influence of these factors on the separation of the analyte enantiomers and the electroosmotic flow was studied. Generally, with tert-butyl carbamoylated quinine as chiral selector, better enantioseparations were achieved than with unmodified quinine. Optimum experimental conditions were found with a buffer made of 12.5 mM ammonia, 100 mM octanoic acid, and 10 mM tert-butyl carbamoylated quinine in an ethanol-methanol mixture (60:40 v/v). Under these conditions, DNB-Leu enantiomers could be separated with a selectivity factor (␣) of 1.572 and a resolution (Rs) of 64.3; a plate number (N) of 127,000 and an asymmetry factor (As) of 0.93 were obtained for the first migrating enantiomer. Chirality 11: 622-630, 1999.

Simultaneous separation of the stereoisomers of 1-amino-2-hydroxy and 2-amino-1-hydroxypropane phosphonic acids by stereoselective capillary electrophoresis employing a quinine carbamate type chiral selector

“…Since CE offers higher efficiency and is therefore supposed to provide higher peak capacity, we tested a previously proposed non aqueous CE method [5,14,19] employing O-(tert-butylcarbamoyl) quinine (Fig. 2a) as chiral additive to a non aqueous background electrolyte for its capability to separate all components of interest in a single run.…”

Chiral separation by chromatographic and electromigration techniques. A Review

“…Stalcup and Gahm [458] used quinine as a ion-pairing reagent in nonaqueous medium for the chiral resolution for acidic compounds using acetic acid-ammonium acetate-methanol as BGE. Piette et al [459] compared native cinchona alkaloids and carbamoylated derivatives for their applicability as chiral ion-pairing reagents for the enantioseparation of N-protected amino acids using ammonium acetate in methanol and ammonia-octanoic acid in an ethanol-methanol mixture as nonaqueous BGEs. In addition to the primary ionic interactions, hydrogen bonding, dipole-dipole, p-p, hydrophobic and steric interactions are to be taken into account.…”

Recent advances in amino acid analysis by capillary electrophoresis

“…Quinine, quinidine, cinchonine, cinchonidine, tertiobutylcarbamoyl quinidine, tertbutylcarbamoylated quinine (TBCQ) and other quinine derivatives were also used as chiral selectors for nonaqueous CE. A separation preference to TBCQ was noticed, and amino acids were used as well as N-protected amino acids [40][41][42].…”