Article ID: 2019.002
The existence of D-amino acids in mammals has been increasingly reported, and clarified that D and L enantiomers have different biological functions, distributions and metabolic pathways. Some D-amino acids were also reported to have a correlation with diseases, and the screening of biomarkers based on quantitative enantioselective metabolomics is highly expected. However, the amounts of most D-amino acids, especially the metabolic-related chiral amino acids, are usually at trace levels in biological samples. Therefore, highly selective and sensitive analytical methods are essential for their accurate determination. In this focusing review, multi-dimensional high-performance liquid chromatographic (HPLC) systems for the precise determination of metabolic-related chiral amino acids are introduced with their application to biological samples. For the highly-sensitive determination, target amino acids were precolumn-derivatized with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F). The multi-dimensional HPLC systems were composed of a reversed-phase column in the 1st dimension and an enantioselective column in the 2nd dimension. By using these systems, various proteinogenic amino acids were clearly observed in the tissues and physiological fluids of rodents. The existence of metabolic-related chiral amino acids in various biological samples were also elucidated.