Characterization of diaminouracil metabolites of caffeine in human urine.
A major caffeine metabolite (A1) has been isolated from human urine by a combination of solvent extraction, reverse phase high-pressure liquid chromatography, and silica gel open column chromatography. The chromatographic and spectral properties of A1 are identical with an authentic sample of 5-acetylamino-6-amino-3-methyluracil. A stable isotope-labeling study, in which [2-14C]caffeine in a 1:1 mixture of unlabeled caffeine and [1,3-15N-8-13C] caffeine was administered to subjects, demonstrated that the C-8 carbon of caffeine was lost during the biotransformation to A1. Thus, the acetyl group in A1 does not originate from caffeine. The 1:1 ratio of the mass spectral ions for A1 isolated from the stable isotope study and the specific activity of A1 support caffeine as the principal source of A1. A related metabolite (A2) was too labile for complete purification and structural identification. The chromatographic and mass spectral properties of the degradation product of A2 were identical with those of A1.
D001711:Biotransformation; D002110:Caffeine / Q000652:urine*; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D002855:Chromatography, Thin Layer; D004586:Electrophoresis; D006801:Humans
D002110:Caffeine