Ligand-exchange chromatography of amino acid enantiomers and its application to the biotransformation of DL-aspartic acid byPseudomonas dacunhae

Enantioselective ligand exchange in modern separation techniques

As a follow-up to a series of review articles on enantioselective ligand exchange chromatography, the present contribution critically evaluates achievements in this area of active and successful research which have been reported in the scientific since 1992. Also discussed is enantioselective ligand exchange in electromigration techniques which have developed especially fruitfully during the last decade.

Analysis of the enzymatic racemization of D-aspartic acid to L-aspartic acid by the on-line coupling of a solid-phase extraction column and a ligand-exchange high-performance liquid chromatography column

D-Aspartic acid can be enzymatically biotransformed with D-amino acid oxidase and aminotransferase to L-aspartic acid. The reaction was surveyed at three temperatures and a period of 3 days, however, L-aspartic acid can be produced only at the reaction temperature 90 degrees C. However, the separation of D-aspartic acid and L-aspartic acid by ligand-exchange chromatography showed matrix interference. Therefore, the column-switching technique by coupling a solid-phase extraction (SPE) column to the analytical ligand-exchange HPLC column was used to eliminate the matrix effect. The pretreatment of reaction samples with the SPE column was considered as a combination of size-exclusion chromatography and ion-pair chromatography. The ion-pair reagent was 0.005 M sodium 1-octanesulfonate aqueous solution adjusted to pH 2.2. Part of the first eluted peak from the SPE column was then switched through the ligand-exchange column and analyzed with a 0.25 mM Cu2+ aqueous mobile phase of pH 3.6. The quantitative analysis of D- and L-aspartic acids was performed by the standard addition method. Overall, the separation and analysis of D- and L-aspartic acids in the enzymic solution was convenient, fast, and successful with the developed on-line LC-LC column-coupling and column-switching system.