Synthesis of [2‐ 14 C]‐1‐(2‐deoxy‐2‐fluoro‐β‐D‐arabinofuranosyl)‐5‐fluoro(chloro)uracil

The reaction of [2‐ 14 C]‐2,4‐bis‐O‐(trimethylsilyl)uracil ( 2 ) with 3‐O‐acetyl‐5‐O‐benzoyl‐2‐deoxy‐2‐fluro‐α‐D‐arabinofuranosyl bromide ( 3 ) yielded the 3‐O‐acetyl‐5‐O‐benzoyl nucleoside 4 which was hydrolyzed with methanolic ammonia to afford [2‐ 14 C]‐1‐(2‐deoxy‐2‐fluro‐β‐D‐arabinofuranosyl)uracil ( 5 ) in 55% radiochemical yield with a specific activity of 2 mCi/mmol (74 MBq/mmol). The reaction of 5 with molecular fluorine and chlorine in glacial acetic acid at 25°C afforded the 5‐fluoro‐ 6a and 5‐chloro‐ 6b analogues of [2‐ 14 C]‐1‐(2‐deoxy‐2‐fluoro‐β‐D‐arabinofuranosyl)uracil in 85.6 and 87.9% isolated radiochemical yield, respectively. Similar radiochemical yields were obtained when [2‐ 14 C]uracil having a specific activity of 12 mCi/mmol (444 MBq/mmol) was utilized.