A very sensitive and specific method of 2-ketoacid determination in various biological fluids using gas chromatography chemical ionization mass spectrometry of O-trimethylsilyl-quinoxalinol derivatives is described. After derivatization with o-phenylenediamine in acidic medium and extraction, the 2-ketoacids, and the 2-ketovaleric acid used as internal standard, are silylated and resolved on a capillary column and their concentrations automatically determined by monitoring the m/z values corresponding to their respective protonated molecular ions, using ammonia as reactant gas. The detection limit is below 50 ng ml-1 of each 2-ketoacid. The recoveries of 2-ketoacids from urine and plasma were between 97 and 104%. Problems encountered with interfering substances were tested for and discussed. This method has been applied successfully to various metabolic disorders characterized by an accumulation of aliphatic 2-ketoacids. The metabolic interrelationship of branched chain 2-ketoacids and other compounds, especially pyruvate, is discussed.

Quantitation of 2‐ketoacids in biological fluids by gas chromatography chemical ionization mass spectrometry of O‐trimethylsily‐quinoxalinol derivatives

Cyclic derivatives for the selective chromatographic analysis of bifunctional compounds

Correlations between branched-chain amino acids and branched-chain α-keto acids in blood in maple syrup urine disease

The α-keto acids of branched-chain amino acids: Simplified derivatization for physiological samples and complete separation as quinoxalinols by packed column gas chromatography

A boy and a girl born to a consanguineous Tunisian couple are suffering from a slowly progressive nervous disorder. Initially they both had normal psychomotor development with acquisition of gait and speech. First symptoms in the boy were athetoid movements during the second year of life. He later lost all motor and language skills and developed muscular rigidity and intention tremor. At the age of five years, he was completely bedridden while he appeared mentally much less affected. His younger sister followed a similar course. The major specific abnormality detected was a strikingly elevated excretion of 2-oxoglutaric acid, which was identified by gas liquid chromatography, mass spectrometry, and enzymatic analysis. 2-oxoglutarate dehydrogenase activity in homogenates of cultured skin fibroblasts was reduced to about 25% of control values in both children. Although the pathogenetic mechanisms leading to brain damage remain obscure, the finding strongly suggest an autosomal recessive neurometabolic disease with predominant involvement of the extrapyramidal system.

A familial progressive neurodegenerative disease with 2-oxoglutaric aciduria.

In acidic media o-phenylenediamine and 2-oxoacids react to yield quinoxaline derivatives. On derivatization in pyridine with silylating reagents quinoxalinol-O-TMS ethers or O-TMS-ether-TMS-esters are formed exclusively as shown by gas chromatography infrared spectrometry and gas chromatography mass spectrometry. These derivatives have very favourable properties for gas chromatographic detection and quantitation of the parent 2-oxoacids. The mass spectra have characteristic fragments which facilitate easy identification. In addition, 'single ion monitoring' of all aliphatic 2-oxoacids can be performed with only three fragments at m/e 217,232 and 245. In some aspects the mass spectra resemble those of other heterocyclic compounds which contain an O-alkyl sidechain. The fragmentation mechanisms were deduced by low resolution mass spectrometry with and without deuteration, high resolution mass spectrometry and metastable ion evidence. A new type of rearrangement alpha-beta-elimination of ethylene or propylene from the aliphatic sidechain, is proposed for some O-TMS quinoxalinols.

Quinoxalinol derivatives of aliphatic 2‐oxocarboxylic acids. Infrared and mass spectra of the O‐trimethylsilylated compounds

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Quinoxalinol derivatives of aliphatic 2‐oxocarboxylic acids. Infrared and mass spectra of the O‐trimethylsilylated compounds