An improved method for synthesis and purification of 125 I or 131 I labeled carrier‐free 5‐iodo‐2′‐deoxyuridine

Consistently high yields (up to 95%) of carrier‐free 5‐iodo‐2′‐deoxyuridine‐ 125 I (or 131 I) can be obtained by iodination of 2′‐deoxyuridine at varying concentrations of radioactive NaI (1–10 mCi), as long as the molarity of deoxyuridine in the reaction mixture is kept at or above 10 −2 M. At lower deoxyuridine molarities the reaction yield is significantly reduced. Several different purification procedures (Biogel P‐2 400 mesh or Sephadex G‐10 column chromatography, paper chromatography with water‐saturated ethyl acetate or water‐saturated butanol) are described. The two column chromatography systems yield iododeoxyuridine of > 95% chemical and radiochemical purity. The two paper chromatography systems are somewhat more involved, but yield 125 I or 131 I labeled 5‐iodo‐2′‐deoxyuridine of > 99% chemical and radiochemical purity.