Tritium labeled prostacyclin sodium salt

Crystalline [11β‐ 3 H]prostacyclin (PGI 2 ) sodium salt (5) was prepared from prostaglandin D 2 (PGD 2 ) methyl ester ( 1 ). Reduction of PGD 2 methyl ester with sodium borotritide afforded [11β‐ 3 H]prostaglandin F 2 α (PGF 2 α) methyl ester ( 2a ) in 57% radiochemical yield. [11β‐ 3 H]PGF 2 α methyl ester was converted via (5R, 6R)‐ and (5S, 6S)‐5‐iodo‐[11β‐ 3 H]prostaglandin I 1 methyl ester ( 3 ) to [11β‐ 3 H]‐prostacyclin methyl ester ( 4 ). Carefully controlled hydrolysis of 4 produced crystalline [11β‐ 3 H]PGI 2 sodium salt which was shown to be >95% pure by means of high performance liquid chromatographic (HPLC) analysis. The overall yield from [11β‐ 3 H]PGF 2 α methyl ester to [11β‐ 3 H]PGI 2 sodium salt was 53%. [11β‐ 3 H]PGI 2 sodium salt with a specific activity of 502 μCi/mg has only limited radiochemical stability. Its radiochemical purity declined 15% after three weeks of storage at −20°C in the crystalline state.