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 electrophore
sis (FZCE) method using cyclodextrin as chiral selector has been developed
and found to be suitable for this purpose. Phenylalanine, tyrosine, tryptop
han, and all of the 3-carboxyphenyl-substituted amino acids (m-carboxytyros
ine, m-carboxyphenylalanine, m-carboxyphenylglycine and m-carboxy-p-hydroxy
phenylglycine) separated well into their enantiomers and from other natural
ly 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 decarb
oxylase, L- and D-amino acid oxidases. The influence of various parameters
on the separation efficiency has been investigated and optimized. Theoretic
al plate numbers of up to 460 000 N . m(-1) have been obtained, and resolut
ions 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 po
ssibility of the racemisation of these compounds, and as a highly specific
and efficient technique for use in amino acid oxidase and decarboxylase ass
ay. (C) 1999 Elsevier Science B.V. All rights reserved.