Chiral separation of aromatic amino acids by capillary electrophoresis

3-Carboxyphenyl-substituted amino acids co-occurring with various types of other aromatic amino acids in plants have been investigated with respect to the chirality at the alpha-carbon atom. A free zone capillary electrophoresis (FZCE) method using cyclodextrin as chiral selector has been developed and found to be suitable for this purpose. Phenylalanine, tyrosine, tryptophan, and all of the 3-carboxyphenyl-substituted amino acids (m-carboxytyrosine, m-carboxyphenylalanine, m-carboxyphenylglycine and m-carboxy-p-hydroxyphenylglycine) separated well into their enantiomers and from other naturally occurring amino acids using the developed FZCE method. Identification of the separated enantiomers has been confirmed by use of authentic reference compounds, by spiking and use of stereospecific aromatic amino acid decarboxylase, L- and D-amino acid oxidases. The influence of various parameters on the separation efficiency has been investigated and optimized. Theoretical plate numbers of up to 460 000 N . m(-1) have been obtained, and resolutions between D- and L-forms in the range from 0.70 to 1.26 (SD<0.10, n=10) of the investigated compounds have been found. The method has been found to be efficient for the determination of the naturally occurring amounts of D- and L-forms of the four meta-carboxy substituted amino acids, with the possibility of the racemisation of these compounds, and as a highly specific and efficient technique for use in amino acid oxidase and decarboxylase assay. (C) 1999 Elsevier Science B.V. All rights reserved.