One‐pot radiosynthesis of [ 13 N]urea and [ 13 N]carbamate using no‐carrier‐added [ 13 N]NH 3

The aim of this study was to develop a practical labeling method of [ 13 N]ligands using no‐carrier‐added [ 13 N]NH 3 with high specific activity. [ 13 N]urea analogues [ 13 N]1a and [ 13 N]2a or [ 13 N]carbamate [ 13 N]3a were synthesized by reacting isocyanate 5a, carbamoyl chloride 6a or chloroformate 7a with [ 13 N]NH 3 . The precursors 5a–7a were prepared by treating amines 8a and 9a and alcohol 10a with triphosgene in situ . These reaction mixtures were not purified and were used directly for [ 13 N]ammonolysis, respectively. Using the one‐pot method, we synthesized [ 13 N]carbamazepine ([ 13 N]4), a putative positron emission tomography ligand for brain imaging. Copyright © 2009 John Wiley & Sons, Ltd.