Thermodynamic enantioseparation behavior of phenylthiohydantoin‐amino acid derivatives in supercritical fluid chromatography on polysaccharide chiral stationary phases

Abstract

Thirteen pairs of enantiomers belonging to the same structural family (phenylthiohydantoin-amino acids) were analyzed on two polysaccharide chiral stationary phases, namely, tris-(3,5-dimethylphenylcarbamate) of amylose (Chiralpak AD-H) or cellulose (Chiralcel OD-H) in supercritical fluid chromatography with a carbon dioxide/methanol mobile phase (90:10 v/v). Five different temperatures (5, 10, 20, 30, 40°C) were applied to evaluate the thermodynamic behavior of these enantioseparations. On the cellulose stationary phase, the retention, and separation trends were most similar among the set of probe analytes, suggesting that the chiral cavities in this stationary phase have little diversity, or that all analytes accessed the same cavities. Conversely, the retention and separation trends on the amylose phase were much more diverse, and could be related to structural differences among the set of probe analytes (carbon chain length in the amino acid residue, secondary amine in proline, existence of covalent rings, or formation of pseudo-rings via intramolecular hydrogen bonds). The large variability of behaviors on the amylose phase suggests that the chiral-binding sites in this chiral stationary phase have more variety than on the cellulose phase, and that the analytes did access different cavities.

Recent Achievements and Future Challenges in Supercritical Fluid Chromatography for the Enantioselective Separation of Chiral Pharmaceuticals

“…Retention mechanism of thirteen pairs of enantiomers belonging to the same structural family (phenylthiohydantoin-amino acids) has been studied on two different polysaccharide stationary phases (Chiralpak AD-H, amylose based and Chiralpak OD-H, cellulose based) at five different temperatures ranging from 5 up to 40 • C. [25] The mobile phase used was CO 2 /methanol 90:10 %v/v. Some structural changes seem to affect both CSPs above 20-30 • C. Below this limit it was found that retention is substantially unaffected by temperature changes on the cellulose based column.…”

Separation and determination of triadimefon and its metabolites triadimenol enantiomers in fruit puree by supercritical fluid chromatography

“…The major mobile phase of this technique is supercritical carbon dioxide (CO 2 ), which shows a higher mass transfer rate and separation efficiency than the traditional organic mobile phase [23]. Research shows that SFC technology is more suitable for the analysis of isomers and structural analogs which can hardly be separated by traditional LC, and has been successfully applied to separate and determine chiral compounds [1,[24][25][26][27][28][29].…”