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

${}^{18}\text{F-labeled}\text{(}\text{E}\text{)-β-}\text{fluoromethylene}\text{-}\text{DL}\text{-m-}\text{tyrosine}$ (FMMT) was prepared by the direct reaction of FMMT with [¹⁸F]acetylhypofluorite (AcOF) resulting into three product isomers. Extensive ¹H, ¹³C and ¹⁹F-NMR spectroscopic analysis identify 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.