Organomediated Cleavage of Benzoyl Group Enables an Efficient Synthesis of 1-(6-nitropyridin-2-yl)thiourea and Its Application for Developing 18F-Labeled PET Tracers.

A novel organomediated cleavage of benzoyl group using ethane-1,2-diamine and acetic acid under neutral condition enables an efficient synthesis of 1-(6-nitropyridin-2-yl)thiourea, which previously has been challenging to prepare by conventional methods. The successful synthesis of 1-(6-nitropyridin-2-yl)thiourea as a synthon permits development of a variety of 18F labeled heterocycles as PET imaging ligands such as N-(pyridin-2-yl)thiazol-2-amine derivatives. The utility of this synthon is demonstrated with the synthesis of a 18F-labeled PET tracer for studying prion disease. In vitro autoradiography using this PET tracer on sagittal rat brain slices showed highest accumulation of radioactivity in the hippocampus, cortex, and striatum, in accordance with reported immunostaining of PrPc in rat brain.