Synthesis of specifically tritium‐labelled oxytocin and lysine‐vasopressin with high specific activity

Highly tritium‐labelled oxytocin and lysine‐vasopressin have been synthesized. L‐tyrosine‐3‐ 3 H was prepared from L‐3‐iodotyrosine and tritium gas in methanolic potassium hydroxide with palladium on active carbon as a catalyst. The tritiated oxytocin and lysine‐vasopressin were obtained from the tritiated tyrosine and the heptapeptides of oxytocin and lysine‐vasopressin, respectively, by the p‐nitrophenyl ester method. The peptides had a high degree of purity and the specific radioactivity was 2.9 C/mmole or 5.9 μC/IU for oxytocin and 1.9 C/mmole or 6.5 μC/IU for lysine‐vasopressin. The high radioactivity of the peptides permits extensive studies of their properties in vivo. The stability of the tritium label is discussed.