Chiral Separation of d,l-p-Hydroxyphenylglycine by Ligand Exchange Micellar Electrokinetic Capillary Chromatography

Abstract

d-p-Hydroxyphenylglycine (d-p-HPG) is an important intermediate for the synthesis of semi-synthetic antibiotics. Owing to the importance of optical purity of d-p-HPG, it is necessary to be able to chirally separate d,l-p-HPG and monitor the enantiomeric purity of d-p-HPG in the pharmaceutical industry. In this work, a Cu(II) complex with l-valine (l-Val) was used as a chiral selector for ligand exchange chiral separation of d,l-p-HPG by micelle electrokinetic capillary chromatography. Optical resolution of d,l-p-HPG was obtained with a running buffer of 20 mM NH₄Ac, 40 mM sodium dodecylsulfate (SDS), 10 mM Cu(II) and 20 mM l-Val at pH 8.5 in less than 10 min. The enantiomer migration order was l-p-HPG before d-p-HPG, which was most suitable for the determination of minor l-p-HPG in the presence of a large excess of d-p-HPG. Separation parameters such as pH, SDS concentration, the molar ratio of Cu(II) to l-Val, the concentration of the chiral metal complex, and capillary temperature were investigated. The present method can also be used for assaying the enantiomeric excess of d-p-HPG.