3-, 6- and 7-hydroxyoctanoic acids are metabolites of medium-chain triglycerides and excreted in urine as glucuronides

J Mass Spectrom. 1996 Jun;31(6):633-8. doi: 10.1002/(SICI)1096-9888(199606)31:6<633::AID-JMS332>3.0.CO;2-L.


Three new metabolites of medium-chain fatty acid oxidation, 3-, 6- and 7-hydroxyoctanoyl beta-D-glucuronide, were identified in the urine of six infants who were fed a diet enriched in medium-chain triglycerides (MCT). Glucuronides were extracted from the urine by organic solvent extraction with ethyl acetate and by solid-phase extraction on Sep-Pak C18 cartridges. The compounds of interest were also purified from the organic solvent extract by preparative one-dimensional thin-layer chromatography. Cleavage of the glucuronides was achieved by either alkaline hydrolysis or enzymatic hydrolysis with beta-D-glucuronidase. The analyses of the trimethylsilylated derivatives were performed both by gas chromatography with flame ionization detection (GC/FID) and by gas chromatography/mass spectrometry (GC/MS). The structure of the hydroxyoctanoic acids was proved by comparison of their mass spectra with those of reference substances. Authentic 6-hydroxyoctanoic acid was synthesized. The presence of 6-hydroxyoctanoyl glucuronide shows that in addition to beta-oxidation, omega-oxidation and (omega-1)-hydroxylation, medium-chain fatty acids can be oxidized at the omega-2 position. The conjugation of medium-chain hydroxy-monocarboxylic acids with glucuronic acid has not been described in humans before.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Caprylates / urine*
  • Chromatography, Thin Layer
  • Diet
  • Flame Ionization
  • Gas Chromatography-Mass Spectrometry
  • Glucuronates / urine
  • Humans
  • Hydrolysis
  • Infant
  • Oxidation-Reduction
  • Triglycerides / urine*


  • Caprylates
  • Glucuronates
  • Triglycerides
  • 7-hydroxyoctanoic acid
  • 6-hydroxyoctanoic acid
  • 3-hydroxyoctanoic acid