Enzymatic-chemical preparation of quinoxaline derivatives from L-amino acids for gas chromatographic-mass spectrometric analyses.
We report on an enzymatic-chemical method for the specific preparation of L-amino acid-derived quinoxalinols suitable for the sensitive estimation of 13C- or 2H-label enrichment by gas chromatography-mass spectrometry: Amino acid fractions are isolated from physiological fluids by ion-exchange chromatography. The compound of interest is converted to the corresponding 2-oxo acid by treatment with an L-amino acid dehydrogenase of the desired specificity. Reaction of the 2-oxo acid with o-phenylenediamine yields the quinoxaline derivative. Isotopic label enrichment is then determined by gas chromatographic-mass spectrometric analysis of the O-trimethylsilyl derivative using an ammonia-chemical ionization mode and selected ion monitoring of the quasi-molecular ions [MH]+ and [MH + n]+ (n = number of labeled positions). Details for application of various generally available L-amino acid dehydrogenases (L-ala DH, L-glu DH, L-leu DH, L-phe DH) are presented. The method was used, e.g., for serum analysis in in vivo studies on the decarboxylation rates of branched-chain L-[1-(13)C]-amino acids.
D000594:Amino Acid Oxidoreductases; D000596:Amino Acids / Q000032:analysis* / Q000097:blood / Q000302:isolation & purification; D002247:Carbon Isotopes; D002852:Chromatography, Ion Exchange / Q000379:methods; D003903:Deuterium; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D006801:Humans; D007202:Indicators and Reagents; D007553:Isotope Labeling; D010649:Phenylalanine / Q000097:blood; D011810:Quinoxalines; D012680:Sensitivity and Specificity
D000596:Amino Acids; D002247:Carbon Isotopes; D007202:Indicators and Reagents; D011810:Quinoxalines; D010649:Phenylalanine; D003903:Deuterium; D000594:Amino Acid Oxidoreductases