Abstract
Although d,l-amino acids are symmetrical molecules, l-isomers are generally dominant in living organisms. However, it has been found that some d-amino acids also have biological functions. A new method for simultaneously analyzing d,l-amino acids in biological samples is required to allow unknown functions of d-amino acids to be investigated. d-Amino acids in urine are currently receiving increasing amounts of attention, particularly for screening for chronic kidney diseases. However, simultaneously analyzing d,l-amino acids in human urine is challenging because of interfering unknown compounds in urine. In this study, the axially chiral derivatizing agent (R)-4-nitrophenyl-N-[2-(diethylamino)-6,6-dimethyl-[1,1-biphenyl]-2-yl] carbamate hydrochloride was used to allow enantiomers of amino acids in human urine to be simultaneously determined by liquid chromatography electrospray ionization tandem mass spectrometry. The optimized method gave good linearities, precision results, and recoveries for 18 proteinogenic amino acids and their enantiomers and glycine. The chiral-switching method using (S)-4-nitrophenyl-N-[2-(diethylamino)-6, 6-dimethyl-[1,1-biphenyl]-2-yl]carbamate hydrochloride confirmed the expected concentrations of 32 of the 37 analytes. The method was successfully used to determine the concentrations of d-serine, d-alanine, d-asparagine, d-allothreonine, d-lysine, and the d-isomers of 10 other amino acids in five human volunteer urine samples.
Highlights
Amino acids play important roles in the body, as the building blocks of proteins and as intermediates in metabolic systems
We developed a method for simultaneously determining d,l-amino acids using the chiral derivatizing agent (R)-biphenyl]-2-yl]carbamate hydrochloride (BiAC)
The presence of some d-amino acids in human urine can indicate kidney diseases, so it is important to develop a method for simultaneously determining chiral amino acids in urine with good sensitivity, throughput, and selectivity
Summary
Amino acids play important roles in the body, as the building blocks of proteins and as intermediates in metabolic systems. D,l-amino acids, a pair of enantiomers, are symmetrical molecules, stereospecific biological reactions accurately control the stereostructures of amino acids, and l-isomers of amino acids are dominant in natural systems. D-isomers are minor enantiomers that have previously been thought not to have biological functions. In the last couple of decades, it has been found that d-amino acids do have biological functions. D-serine (Ser) [1,2,3,4] and d-aspartate (Asp) [5,6,7,8] have biological functions in the brain and nervous system that have been investigated intensively. D-amino acids in blood have recently been investigated as potential biomarkers [9] D-serine (Ser) [1,2,3,4] and d-aspartate (Asp) [5,6,7,8] have biological functions in the brain and nervous system that have been investigated intensively. d-amino acids in blood have recently been investigated as potential biomarkers [9]
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