Isolation and identification of 5-acetylamino-6-formylamino-3-methyluracil as a major metabolite of caffeine in man.

An acetylated metabolite produced in man after po administration of caffeine was detected, isolated, and purified using suitable solvent extraction and chromatographic techniques. A set of UV, NMR, and mass spectral data identify it as 5-acetylamino-6-formylamino-3-methyluracil, a structure confirmed by chemical synthesis. This metabolite was shown to be unstable in the presence of dilute base and/or methanol, giving rise to a deformylated compound, 5-acetylamino-6-amino-3-methyluracil, which had recently been reported in the literature as a major metabolite of caffeine in man.