An automated radiosynthesis of 2-[11C]thymidine using anhydrous [11C]urea derived from [11C]phosgene

2-[11C]Thymidine has been produced from [11C]methane via [11C]phosgene and [11C]urea. Anhydrous [11C]urea was prepared from [11C]phosgene by reaction with liquid ammonia. This novel approach avoids the problems associated with the synthesis of anhydrous [11C]urea from [11C]cyanide. A fully automated system based on a modular approach and under PLC control has been developed. The system provides 2-[11C]thymidine reliably and reproducibly for clinical PET studies. The radiosynthesis takes 45–50 min from [11C]methane and the average yield was 1.5–3.3 GBq (40–90 mCi). The specific radioactivity was typically in the range 29.6–51.8 GBq μmol−1 (0.8–1.4 Ci μmol−1) at EOS corresponding to 6–12 μg of stable thymidine. The radiochemical yield of 2-[11C]thymidine was ca. 14% from [11C]methane.