High yield synthesis of 6-[18F]fluoro-L-dopa by regioselective fluorination of protected L-dopa with [18F]acetylhypofluorite.

Regioselective fluorination of a completely protected phosgene derivative of 3,4-dihydroxy-phenyl-L-alanine (5-(benzyl-3',4'-carbonate)-oxazolidine-2,5-dione) with gaseous 18F-labeled acetylhypofluorite and [18F]F2 in acetonitrile is described. Fluorination with [18F]acetylhypofluorite yields 6-[18F]fluoro-L-dopa with 95% radiochemical purity; fluorination of the same substrate with [18F]F2 yields a mixture of all three structural isomers in a ratio of 70:16:14 for 6-, 5-, and 2-fluoro compounds. Radiochemical yield, relative to [18F] acetylhypofluorite, measured at the end of the synthesis, is (21 +/- 4)% (N = 8). The synthesis requires approximately 40 min (50 min if HPLC was done) and yields the final radiopharmaceutical in a two-step procedure. The specific activity of the final product was approximately 763 mCi/mmol at the end of a 40-min synthesis when 30-min irradiation was used.