Enantioseparation of ß-carboline derivatives on polysaccharide- and strong cation exchanger-based chiral stationary phases. A comparative study

Abstract

In this study we attempted to describe in a comparative manner the enantioselectivity performance of six different polysaccharide- and two strong cation exchanger-type chiral stationary phases (CSPs) for the resolution of free and N-protected β-carboline derivatives. On commercially available cellulose- or amylose-based CSPs, the enantioseparations were carried out in normal-phase mode by variation of the nature and the concentration of the alcohol modifier in n-hexane as mobile phase. With the application of strong cation exchanger-type CSPs, the enantioseparations were optimized by the variation of methanol-acetonitrile bulk solvent compositions in the presence of various amounts of acid and base additives acting as counter-ions. Detailed thermodynamic investigations revealed that in all cases the enantioseparations observed were enthalpically driven, i.e. the retention and selectivity decreased with increasing temperature. Elution sequences were determined routinely; no general rule was found on polysaccharide-based CSPs, while on the two enantiomeric strong cation exchanger-type CSPs the predicted reversal of the elution sequence could be confirmed on switching from one enantiomeric CSP to the other form.

Liquid chromatographic enantioseparation of limonene‐based carbocyclic β‐amino acids on zwitterionic Cinchona alkaloid‐based chiral stationary phases

“…The slopes of the log k versus log c plots in this study (0.25–0.31) are in accordance with our results obtained on ZWIX phases working in zwitterionic mode . However, ZWIX phases working in a “uni‐ionic” mode as anion‐exchanger or cation‐exchanger exhibited steeper slopes (0.6–1.0). These values indicate a marked difference between the concerted zwitterionic and a “uni‐ionic” ion‐exchange mechanism.…”

Liquid and supercritical fluid chromatographic enantioseparation of Nα‐Fmoc proteinogenic amino acids on Cinchona alkaloid-based chiral stationary phases

“…The slopes of these plots are given by the ratio of the effective charges of SA and counter-ion. This slope was close to 1.0 in the case of the single cation-exchanger type CSPs [87].…”

Design and synthesis of naphthalene‐based chiral strong cation exchangers and their application for chiral separation of basic drugs

“…CSPs prepared therefrom showed very good enantioselectivity toward Cinchona alkaloids [23]. Noteworthy, it was capable to enantiomerically resolve also a broad range of other chiral amines [24,25].…”