ABSTRACT
Stereoselective high-performance liquid chromatographic separations of eight sterically constrained cyclic ß-amino acid enantiomer pairs were carried out using the newly developed Cinchona alkaloid-based zwitterionic chiral stationary phases Chiralpak ZWIX(+) and ZWIX(-). The effects of the mobile phase composition, the nature and concentrations of the acid and base additives, the counterions and temperature on the separations were investigated. The changes in standard enthalpy, Δ(ΔH°), entropy, Δ(ΔS°), and free energy, Δ(ΔG°), 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 and the structures of the analytes. Unusual temperature behavior was observed on the ZWIX(-) column: decreased retention times were accompanied by increased separation factors with increasing temperature. On the ZWIX(+) column only enthalpically, whereas on the ZWIX(-) column both enthalpically and entropically driven separations were observed. The elution sequence was determined in all cases and was observed to be the opposite on ZWIX(+) and on ZWIX(-).
Subject(s)
Amino Acids, Cyclic/chemistry , Amino Acids, Cyclic/isolation & purification , Chromatography, High Pressure Liquid/methods , Cinchona Alkaloids/chemistry , Stereoisomerism , Temperature , ThermodynamicsABSTRACT
A novel gas chromatographic method was developed for the enantioseparation of valuable acyclic and carbocyclic cis- and trans-beta-amino acids, including cispentacin and a number of its analogues and homologues. Excellent (in most cases baseline) separation was achieved for the racemates of these beta-amino acids on CP-Chirasil-Dex CB or CP-Chirasil L-Val columns after a simple and rapid double derivatization (esterification followed by N-acylation). The elution sequences were determined in all cases.
Subject(s)
Amino Acids, Cyclic/isolation & purification , Chromatography, Gas/methods , Amino Acids, Cyclic/chemistry , Cyclodextrins/chemistry , Cycloleucine/analogs & derivatives , Cycloleucine/isolation & purification , Organic Chemicals/chemistry , Reproducibility of Results , Sensitivity and Specificity , Siloxanes/chemistry , StereoisomerismABSTRACT
The kinetic resolution of alpha-trifluoroacetamido N-acyl oxazolidinethiones using 5-10% of the chiral, nonracemic O-nucleophilic acyl transfer catalyst 2 is described. A variety of substrates participate in this reaction in excellent yields, with s-factors ranging from 20 to 86.
Subject(s)
Amino Acids, Cyclic/chemistry , Amino Acids, Cyclic/isolation & purification , Catalysis , Hydrogen Bonding , Imides/chemistry , Kinetics , Oxazoles/chemistry , Oxazoles/isolation & purification , Stereoisomerism , Thiones/chemistry , Thiones/isolation & purificationABSTRACT
High-performance liquid chromatographic (HPLC) separation of stereoisomeric cyclic beta-substituted alpha-quaternary alpha-amino acids was performed by ligand-exchange on a copper(II)-D-penicillamine chiral stationary phase. The investigated amino acids are the 1-amino-2-methylcyclohexanecarboxylic acids, the 1-amino-2-hydroxycyclohexanecarboxylic acids, the 1-amino-2-methylcyclopentanecarboxylic acids and the trans-configured 1,2-diaminocyclohexanecarboxylic acids. The effects of the mobile phase composition (copper(II) concentration, type and content of organic modifier, pH) and the temperature on the enantio- and diastereoselectivity were studied and the conditions were optimised to resolve the four stereoisomers of each of the said amino acids in single chromatographic runs. A reversal of the elution order occurred for enantiomers of some of the amino acids in dependence on the acetonitrile content of the eluent. This phenomenon is explained by at least two different copper(II) complexes of the tridentate ligand penicillamine.
