Isovalerylglucuronide, a new urinary metabolite in isovaleric acidemia. Identification problems due to rearrangement reactions.

Isovaleryl-beta-D-glucuronide, a new metabolite in the urine of patients with isovaleric acidemia, is described. Its gas chromatographic and mass spectrometric parameters are presented. In alkaline solution this glucuronide exhibited intramolecular rearrangements, resulting in isomers bearing the acyl moiety on C-2, C-3 and C-4. The isomers showed similar mass spectra but different positions on the gas chromatogram. In the index patient isovalerylglucuronide was a main metabolite, but the excretion was a transient phenomenon. Only traces of isovalerylglucuronide could also be detected in the urine of three other patients with isovaleric acidemia. The significance of this metabolite for the detoxication of isovalerate in isovaleric acidemia is discussed.