Abstract
The focus of this contribution is a comparative investigation of enantioseparations of 19 Nα-Fmoc proteinogenic amino acids on Quinine-based zwitterionic and anion-exchanger type chiral stationary phases employing hydro-organic and polar-ionic liquid and subcritical fluid chromatographic conditions. Effects of mobile phase composition (including additives, e.g., water, basis and acids) and nature of chiral selectors on the chromatographic performances were studied at different chromatographic modes. Thermodynamic parameters of the temperature dependent enantioseparation results were calculated in the temperature range 5–50 °C applying plots of lnα versus 1/T. The differences in standard enthalpy and standard entropy for a given pair of enantiomers were calculated and served as a basis for comparisons. Elution sequence in all cases was determined, where a general rule could be observed, both in liquid and subcritical fluid chromatographic mode the d-enantiomers eluted before the L ones. In both modes, the principles of ion exchange chromatography apply.
Highlights
The stereochemical purity of biologically active compounds became a strongly emerging issue in the last decades, which eventually impacted the synthetic concepts of drugs and intermediates and the related analytics
We present results obtained on the enantioseparation of Nα -Fmoc protected proteinogenic amino acids (Figure 1) on Cinchona alkaloid quinine (QN)-based zwitterionic and weak anion exchanger-type chiral stationary phases (Figure 2) in hydro-organic (HO) and polar-ionic (PI)
Under all the chromatographic conditions applied in this study, retention was found to be primarily based on ionic interactions, whereas additional intermolecular interactions were responsible for chiral discrimination
Summary
The stereochemical (chiral) purity of biologically active compounds became a strongly emerging issue in the last decades, which eventually impacted the synthetic concepts of drugs and intermediates and the related analytics. Molecules 2016, 21, 1579 presence must be analytically controlled [1,2]. In addition to problems in drug discovery, the e.e. issues are of importance for the successful chemical synthesis of different biomolecules including therapeutic peptides and proteins [3]. For multistep syntheses concepts involving chiral synthons their rigorous chemical and stereochemical purity control is highly demanded and often a challenging task [4]. As a great variety of Nα -protected amino acids serves as building blocks (chiral synthons) for modern peptide syntheses, there is a great need to control and analyze them with high sensitivity
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