Abstract
With the exception of glycine, α-amino acids are optically active, and two optical isomers (L- and D-) of each amino acid can be formed. Recent developments of analytical techniques have revealed that several free D-amino acids such as D-aspartate, D-serine and D-alanine exist in many kinds of organism including human and have biologically important roles. D-Aspartate regulates reproductive activity in animals and humans. D-Serine serves as a co-agonist of the N-methyl-D-aspartate receptor, which mediates glutamatergic neurotransmission. D-Alanine plays a role like osmolyte in crustaceans and mollusks. In this protocol, we describe a method for analysis of L- and D-amino acids using ultra-performance liquid chromatography (UPLC). To analyze D- and L-amino acids, the enantiomers are initially converted into diastereomers (diastereomers are stereoisomers that are not related as object and mirror image and are not enantiomers) using pre-column derivatization with o-phthaldialdehyde plus N-acylated cysteine (N-acethyl-L-cysteine or N-tert-butyloxycarbonyl-L-cysteine). The resultant derivatives are fluorescent diastereomers. This is followed by separation of the resultant fluorescent isoindol derivatives on an octadecylsilyl stationary phase using UPLC, and the fluorescence is detected by a fluorescence detector included in UPLC system. Using this method, 16 kinds of D-amino acid can be analyzed.
Materials and Reagents
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Representative data
Instability of the column temperature negatively affects reproducibility of separation of two neighboring peaks (for example, peaks of D-histidine and L-histidine in the case of OPA-NAC derivatization). We recommend that you keep the column temperature at 30 °C accurately.
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Acknowledgments
In this method, we have modified Aswad’s and Hashimoto’s methods for the derivatization of amino acids using OPA and chiral thiols (NAC and NBC). In addition, this work was supported by a grant for Promotion of Basic Research Activities for Innovate Bioscience from the Bio-oriented Technology Research Advancement Institution (BRAIN) and JSPS KAKENHI Grant Number 2402734.
References
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