2-¹⁴C-1-(2′-deoxy-β-D-ribofuranosyl)-5-ethyluracil: Synthesis and biotransformation in rats

With ¹⁴C-urea as the starting material, 2-¹⁴C-1-(2′-deoxy-β-D-ribofuranosyl)-5-ethyluracil [2-¹⁴C-β-5-ethyl-2′-deoxyuridine] was synthesized for metabolic studies. After intravenous administration in rate, 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.