Towards the chiral metabolomics: Liquid chromatography–mass spectrometry based dl-amino acid analysis after labeling with a new chiral reagent, (S)-2,5-dioxopyrrolidin-1-yl-1-(4,6-dimethoxy-1,3,5-triazin-2-yl)pyrrolidine-2-carboxylate, and the application to saliva of healthy volunteers

• Published in: Analytica chimica acta Vol. 875; pp. 73 - 82
• Main Authors: Mochizuki, Toshiki, Takayama, Takahiro, Todoroki, Kenichiro, Inoue, Koichi, Min, Jun Zhe, Toyo’oka, Toshimasa
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 22.05.2015
• Subjects: Adult; Amino acids; Amino Acids - analysis; Chiral derivatization reagent; Chiral metabolomics; Chromatography, High Pressure Liquid - methods; Dicarboxylic Acids - chemistry; Female; Humans; Indicators and Reagents - chemistry; Male; Mass spectrometry; Metabolomics - methods; Pyrrolidines - chemistry; Reproducibility of Results; Reversed-phase chromatography; Saliva - chemistry; Saliva analysis; Spectrometry, Mass, Electrospray Ionization - methods; Stereoisomerism; Tandem Mass Spectrometry - methods; Young Adult; Amino acids; Saliva analysis; Chiral derivatization reagent; Reversed-phase chromatography; Mass spectrometry; Chiral metabolomics
• ISSN: 0003-2670; 1873-4324
• DOI: 10.1016/j.aca.2015.02.054

[Display omitted] •A novel chiral labeling reagent was synthesized.•Analysis of dl-amino acids was performed by UPLC–ESI-MS/MS.•Efficient enantioseparation and detection of dl-amino acids were performed.•dl-Amino acid in saliva was successfully determined under mild conditions. A novel triazine-type chiral derivatization reagent, i.e., (S)-2,5-dioxopyrrolidin-1-yl-1-(4,6-dimethoxy-1,3,5-triazin-2-yl) pyrrolidine-2-carboxylate (DMT-(S)-Pro-OSu), was developed for the highly sensitive and selective detection of chiral amines and amino acids by UPLC–MS/MS analysis. The enantiomers of amino acids were easily labeled with the reagents at room temperature within 40min in an alkaline medium containing triethylamine. The diastereomers derived from proteolytic amino acids, except serine, were well separated under isocratic elution conditions by reversed-phase chromatography using an ODS column (Rs=1.2–9.0). dl-Serine was separated by use of an ADME column which has relatively higher polar surface than the conventional ODS column. The characteristic product ions, i.e., m/z 195.3 and m/z 209.3, were detected from all the diastereomers by the collision-induced dissociation of the protonated molecule. A highly sensitive detection on the amol–fmol level was obtained from the selected reaction monitoring (SRM) chromatogram. The chiral amines (e.g., adrenaline and noradrenaline) labeled with DMT-(S)-Pro-OSu were also well separated and sensitively detected by the present procedure. The method using DMT-(S)-Pro-OSu was used for the determination of dl-amino acids in the human saliva from healthy volunteers. Various l-amino acids were identified in the saliva. Furthermore, d-alanine (d-Ala) and d-proline (d-Pro) were also detected in relatively high concentrations (>5%). The ratio was higher in male saliva than in female saliva. However, the difference in the ratio of d-Ala for one day was not very high and the effect of foods and beverage seemed to be negligible. Based on the results using l-Ala-d3, the d-Ala in saliva seemed to be produced due to the racemization with some enzymes such as racemase. The racemization reaction was reversible, i.e., d-Ala-d3 was also racemized to l-Ala-d3 in saliva. Thus, care should be taken during the analysis of dl-amino acids in saliva. The present method using DMT-(S)-Pro-OSu may be applicable for the determination of chiral amine metabolomics, because the resulting derivatives produce the same product ions without relation to the compounds and show highly sensitive detection in the SRM mode of MS/MS. Consequently, DMT-(S)-Pro-OSu seems to be a useful chiral derivatization reagent for the determination of amines and amino acids in biological samples.