Radiochemical and NMR spectroscopic investigation of the solvent effect on the electrophilic elemental fluorination of L-DOPA: synthesis of [18F]5-fluoro-L-DOPA

Differences in reactivity and selectivity of fluorine in the electrophilic fluorination of 3,4-dihydroxy phenyl-L-alanine (L-DOPA) in different solvents have been exploited to produce mCi quantities of [18F]5-fluoro-L-DOPA. Proton and 13C NMR spectroscopy have been used to show that, while the orientation of electrophilic fluorination of L-DOPA in weak acids (trifluoroacetic acid, 10% trifluoroacetic acid in glacial acetic acid and formic acid) is influenced by the electron donating OH groups on the ring, the orientation of electrophilic fluorination of L-DOPA in strong acids (HF and HF/BF3) is mainly influenced by the side-chain.