An efficient new method for the synthesis of 3-[18 F]fluoro-4-aminopyridine via Yamada-Curtius rearrangement.

4-Aminopyridine is a clinically approved drug to improve motor symptoms in multiple sclerosis. A fluorine-18-labeled derivative of this drug, 3-[18 F]fluoro-4-aminopyridine, is currently under investigation for positron emission tomography (PET) imaging of demyelination. Herein, the Yamada-Curtius reaction has been successfully applied for the preparation of this PET radioligand with a better radiochemical yield and improved specific activity. The overall radiochemical yield was 5 to 15% (n = 12, uncorrected) with a specific activity of 37 to 148 GBq/μmol (end of synthesis) in a 90 minute synthesis time. It is expected that this 1 pot Yamada-Curtius reaction can be used to prepare similar fluorine-18-labeled amino substituted heterocycles.