Synthesis of radiobrominated m-tyrosine

Synthesis of 4-[18F]fluoro-L-m-tyrosine: a model analog for the in vivo assessment of central dopaminergic function

4-[18F]Fluoro-L-m-tyrosine (6), a new analog of L-dopa for probing the presynaptic dopaminergic system by positron emission tomography has been synthesized in good radiochemical yields via the regioselective fluorodemercuration of the 4-mercurio derivatives 4a and 4b with 18F-labeled acetylhypofluorite. The chemical, radiochemical and enantiomeric purities were determined to be greater than 99%. The key step in the synthesis of the precursors 4 was the mercuration of the protected L-m-tyrosine 3. The position of mercuration on the aromatic ring was gleaned from the 13C-NMR spectral data. The non-radiolabeled counterpart of 6 was also synthesized. Structural analyses of all these compounds were carried out by 1H-, 13C-, 19F-NMR and mass spectroscopy.

Synthesis of radiofluorinated analogs of m-tyrosine as potential L-dopa tracers via direct reaction with acetylhypofluorite

The direct electrophilic radiofluorination of m-tyrosine using [18F]acetylhypofluorite was investigated. Results showed that this reaction was both rapid and efficient with recovered decay corrected yield of 71% radiofluorinated m-tyrosines based on starting [18F]acetylhypofluorite. Specific activity of the product obtained in this study was 100-200 mCi/mmol although 1-5 Ci/mmol are easily achievable with our improved production of [18F]AcOF. Three positional isomers were found and identified by 19F-NMR to be 2-, 4-, 6-fluoro-m-tyrosine with a distribution of 36:11:52, respectively. This measured distribution allowed the assignment of the radio-HPLC peaks. Biological studies are currently underway in our laboratory using these fluoro-m-tyrosines to determine which isomer would be most suited for the evaluation of the dopamine system by positron tomography.