Synthesis of [2- ^<14>C,5- ^3H]Cytosine using Bromine and Tritium Gas-III

A study for improving the yield in the synthesis of ［2-14C，5-3H］cytosine was made using a preferable condition for the reaction between ［2-14C，5-Br］ cytosine and tritium gas. Using ［2-14C］ cytosine as the starting material, 29% of radioactive cytosine was recovered after bromination and tritiation. Tritium labeled in the product obtained was determined to 86%. Thus, the degree of double labeling was calculated as 70% on the basis of the radioactive content of the starting cytosine (81%).