Enantioseparation of chiral amino acids as the N(O,S)-ethoxycarbonylated diastereomeric esters by achiral dual-capillary column gas chromatography

摘要

The enantioseparation of 30 racemic amino acids in a single analysis is described for the determination of their absolute configurations.Two-phase extractive ethoxycarbonyl (EOC) reaction with ethyl chlorofomate present in the dichloromethane phase was performed to recover amino acids from alkaline aqueous solutions.The resulting N,(O,S),EOC amino acids extracted into an organic solvent after acidification were reacted with a chiral alcohol such as (S)-(+)-3-methylbutan-2-ol,(S)-(+)-butan-2-ol and (S)-(+)-octan-2-ol for gas chromatographic analysis on achiral dual-capillary DB-5 and DB-17 columns of different polarities.Among the chiral reagents examined,(S)-(+)-3-methylbutan-2-ol provided the best diastereomeric structures in resolving all te racemic amino acids into their enantiomeric paris with high resolution factors (1.2-8.0).Moreover,the temperature-programmed retention index (I) values measured on the two columns were characteristic of each enantiomer.Hence simple I matching with the reference values was useful in cross-checking for chemical identification and also chiral discrimination.When the present method was applied to a fermented dairy product (Yakult),D-alanine,D-aspartic acid,D-glutamic acid and D-proline were positively detected along with their respective L-forms in addition to glycine.