Efficient preparation of 6-[18F]fluoroveratraldehyde, the precursor of the multi-step synthesis of [18F]FDOPA

As a clinically well established PET tracer, 6[F-18]fluoro-L-dopa is prepared by a multi-step synthesis if [F-18]fluoride is to be used for labelling. The [F-18] label is introduced in the first step, i.e. 6-[F-18]fluoroveratraldehyde is prepared first with yields reported in the literature ranging between 20 and 50%. To obtain higher over-all yields in the synthesis of 6-[F-18]fluoro-L-dopa, the F-18 incorporation in the first step was optimised by determining the yield dependencies on solvent, concentration of the precursor, temperature and time of the reaction. Thus, the product is formed with a yield of 89 +/- 2% (n = 15) when using 20 mg of 6-nitroveratraldehyde in 1 mL DMF at 140 degrees C within a reaction time of 10 min.