Capillary zone electrophoresis monitoring of enantioselective hydrogenation ofN-acyldehydroamino acids

Abstract

The use of capillary zone electrophoresis (CZE) for the separation and quantitation of N-acetyl-phenylalanine enantiomers and (Z)-α-acetamido cinnamate was studied in the context of asymmetric hydrogenation of N-acyldehydroamino acids catalyzed by Rh(I)-ferrocenylphosphine complexes. Host-guest complexation of these separands, having identical or very close actual ionic mobilities, with 6'-deoxy-6'-methylamino-β-cyclodextrin (MA-β-CD) were found to effect their resolution in a single CZE run. On use of MA-β-CD, reliable CZE identification and quantitation of N-acetyl-phenylalanine enantiomers and (Z)-α-acetamido cinnamate in the reaction mixtures were accomplished on the basis of the response of a photometric absorbance detector operating at a 200 nm detection wavelength. For example, the migration times of these reaction constituents agreed within 0.3-0.4% in repeated CZE runs while the enantiomers could be determined with 0.8-1.6% RSD. The elaborated CZE procedure made it possible to reliably determine the relative abundance of the enantiomers in the reaction mixtures under differing catalytic conditions with only minimum sample preparation.