Comparison of the Separation Performances of Cinchona Alkaloid-Based Zwitterionic Stationary Phases in the Enantioseparation of β2- and β3-Amino Acids

Abstract

Abstract:The enantiomers of twelve unusual β 2 -and β 3 -homoamino acids containing the same side-chains were separated on chiral stationary phases containing a quinine-or quinidine-based zwitterionic ion-exchanger as chiral selector. The effects of the mobile phase composition, the nature and concentration of the acid and base additives and temperature on the separations were investigated. The changes in standard enthalpy, ∆(∆H°), entropy, ∆(∆S°), and free energy, ∆(∆G°), were calculated from the linear van't Hoff plots derived from the ln α vs. 1/T curves in the studied temperature range (10-50 °C). The values of the thermodynamic parameters depended on the nature of the selectors, the structures of the analytes, and the positions of the substituents on the analytes. A comparison of the zwitterionic stationary phases revealed that the quinidine-based ZWIX(−)™ column exhibited much better selectivity for both β -amino acids. The elution sequence was determined in some cases and was observed to be R < S and S < R on the ZWIX(+)™ and ZWIX(−)™ columns, respectively.

High‐Performance Liquid Chromatographic Enantioseparation of Cyclic β‐Amino Acids on Zwitterionic Chiral Stationary Phases Based on Cinchona Alkaloids

“…However, on the ZWIX(−) column with mobile phase a , the behavior of the pair 1A , 1B was unusual: with increasing temperature, k decreased, but α and R S increased. Such behavior was recently observed for other unusual amino acids too …”

Fundamental Developments of Chiral Phase Chromatography in Connection with Enantioselective Synthesis of β‐Amino Acids

“…(a) Brush‐type chiral stationary phases (or selector‐based chiral sorbent), that usually consist in small chiral molecules immobilised onto an achiral support (e. g., organic polymers or silica gel particles). Chiral metal complexes, crown ethers,, cyclodextrins,, antibiotics, Pirkle‐type receptors, zwitterionic quinine‐based selectors, among others enter in this category.…”

Determination of Enantioselectivities by Means of Chiral Stationary Phase HPLC in Order to Identify Effective Proline-Derived Organocatalysts

“…Chiral metal complexes, 16 crown ethers, 17 cyclodextrins, 18 cyclofructans, 19 antibiotics, 20 Pirkle-type receptors, 21 zwitterionic quinine-based selectors, 22 among others enter in this category. 23 (ii) Sorbents based on optically active polymers, which can be synthetic such as the molecularly imprinted polymers 24 or obtained from natural sources, e.g.…”