2-14C-1-(2'-deoxy-beta-D-ribofuranosyl)-5-ethyluracil: synthesis and biotransformation in rats

With 14C-urea as the starting material, 2-14C-1-(2'-deoxy-beta-D-ribofuranosyl)-5-ethyluracil [2-14C-beta-5-ethyl-2'-deoxyuridine] was synthesized for metabolic studies. After intravenous administration in rats, the radioactivity disappeared in the blood within 72 hr, being eliminated primarily in the urine (97%). The major elimination took place in the first 24 hr (92%). Little radioactivity was detected in the organs and tissues after 3 days. Approximately 50% of the urine radioactivity probably was due to an unidentified conjugate, 30% was due to Metabolite II, and 20% was unchanged drug. Metabolite II was identified as 5-ethyluracil by mass and 1H-NMR spectra and by comparison with an authentic sample.