[18F]fluoro-β-fluormethylene-m-tyrosine analogs, potential PET agents for presynaptic dopamine terminals: synthesis and spectroscopic characterization

18F-labeled (E)-β-fluoromethylene-DL-m-tyrosine (FMMT) was prepared by the direct reaction of FMMT with [18F]acetylhypofluorite (AcOF) resulting in three product isomers. Extensive 1H, 13C and 19F-NMR spectroscopic analysis identified these products to be 2-fluoro, 6-fluoro-FMMT and 2,6-difluoro-FMMT. The HPLC isolated radiochemical EOB yields of these products were 22, 25 and 14%, respectively, based on starting [18F]AcOF. The specific activity at the end of a synthesis time of an hour was ca 200 mCi/mmol. With the possible advantage of ''metabolic trapping'' in dopamine nerve terminals via covalent binding to MAO and reduced metabolite formation, [18F]F-FMMT may potentially be the optimal PET tracer for CNS dopamine nerve terminals. (author)