Stereodifferentiation of 3-hydroxyisobutyric- and 3-aminoisobutyric acid in human urine by enantioselective multidimensional capillary gas chromatography-mass spectrometry

The chiral metabolites 3-hydroxyisobutyric acid (HIBA) and 3-aminoisobutyri c acid (AIBA) are intermediates in the pathways of L-valine and thymine and play an important role in the diagnosis of the very rare inherited metabol ic diseases 3-hydroxyisobutyric aciduria (McKusick 236975) and methylmaloni c semialdehyde dehydrogenase deficiency (McKusick 603178-MSDD). Until now o nly a few approaches have been made in enantioselective analysis of HIBA an d AIBA and for that reason very little information is available on enantiom eric ratios of these metabolites in man. This paper reports on the simultan eous stereodifferentiation of HIBA and AIBA in human urine as corresponding N(O)-methoxycarbonyl methyl esters by derivatization with methyl chlorofor mate (MCF) using enantioselective multidimensional gas chromatography-mass spectrometry (enantio-MDGC/MS) with heptakis-(2,3-di-O-methyl-6-Q-tert.-but yl-dimethylsilyl)-beta-cyclodextrin as the chiral stationary phase. During this investigation urine samples from different patients and healthy contro ls were analyzed in order to reveal characteristic enantiomeric patterns of these metabolites. A trend of dominating R-HIBA excretion in the control u rine samples investigated was observed. An excretion of more than 80% S-HIB A was found in the urines of two patients with ketonemic vomiting. There ar e some clues indicating a possible renal reabsorbtion of S-HIBA similar to those of S-AIBA. Furthermore, there was a significant Ending with regard to the enantiomeric of AIBA in a patient with MSDD - a markly increased excre tion of the S-enantiomer in contrast to the other samples. Using the enanti omeric ratios of AIBA, a previously investigated case of benign methylmalon ic aciduria (bMMA) could be excluded from the diagnosis of MSDD. (C) 2000 E lsevier Science B.V. All rights reserved.