THIN-LAYER CHROMATOGRAPHIC EVIDENCE OF PROLINE PEPTIDIZATION IN SOLUTION AND ITS THIN-LAYER CHROMATOGRAPHIC ENANTIOSEPARATION

Abstract

Direct enantioseparation of underivatized amino acids dissolved in the aqueous and nonaqueous solvents by means of the chiral TLC is a difficult analytical task. Most often such enantioseparations are carried out for the derivatized amino acids, or by means of the ion-exchange chromatography or electrophoresis. The main reasons of the aforementioned difficulty seem an ability of the chiral low molecular weight carboxylic acids (amino acids included) to undergo spontaneous condensation and spontaneous chiral conversion, as confirmed, for example, by the results of our earlier studies. In this study, we provide an experimental evidence of rapid peptidization of L-proline and DL-proline obtained by means of the two different TLC systems, additionally confirmed by LC/MS and ¹H NMR spectroscopy. Additionally, a novel TLC system for the direct enantioseparation of DL-proline is proposed, which considerably outperforms earlier elaborated systems. Finally, relevant practical conclusions are drawn.

Keywords:

• 1H NMR
• LC/MS
• proline
• spontaneous peptidization
• TLC enantioseparation

ACKNOWLEDGMENT

The authors wish to acknowledge helpful discussions with Professor Ravi Bhushan (Indian Institute of Technology, IIT, Roorkee, India) and Professor Krzysztof Kaczmarski (Technical University, Rzeszów, Poland), and the generous free donation of the silica gel coated ProteoChrom plates by the firm Merck KGaA (Merck, Darmstadt, Germany).