1H NMR spectra of methylcitric acid in urine.

Abstract

Methylcitric acid (3-carboxy-3-hydroxy-2-methyl-pentanedioic acid; MCA) is elevated in body fluids of patients with propionic acidaemia (PA; McKusick: 232000, 232050), methylmalonic aciduria (MMA; McKusick: 251000, 251120) and multiple carboxylase deficiency (McKusick: 253260, 253270). MCA molecule has two stereogenic centers so that it can occur in the form of four stereoisomers. Only two stereoisomers of MCA, (2S, 3S) and (2R, 3S), were found in human urine. They have different spectra and can be easily distinguished. We performed measurements of 1H, 13C NMR and gs-HMQC (gradient-selected Heteronuclear Multiple Quantum Coherence) on the samples of unprocessed urine of 6 patients suffering from propionic acidaemia and methylmalonic aciduria and identified the protons of MCA diastereoisomers, 3-hydroxypropionic acid and methylmalonic acid. Having used NMR spectroscopy to identify stereoisomers of MCA in urine, we can conclude that this technique gives the possibility of analysing MCA diastereoisomers in body fluids.