Synthesis of L‐[5‐¹¹C]ornithine

No‐carrier‐added L‐[5‐¹¹C]ornithine was synthesized in 25–40% radiochemical yield in a synthesis time of 50 min (EOB) and a specific activity >2.1 Ci/umol by the displacement reaction of potassium [¹¹C]cyanide with the functionally protected y‐bromohomoserine followed by selective reduction of the [¹¹C]nitrile with cobalt chloride‐sodium borohydride complex, deprotection with 6M HCl(aq), and purification by HPLC. During the course of these studies it was found that cyanide ion is generated from acetonitrile in the presence of potassium hydroxide and kryptofix 222.