Efficient Copper-Mediated Radiosynthesis of 6-[18F]Fluoro-L-DOPA ([18F]FDOPA) in a Microreactor

Objectives: The diagnostic radiopharmaceutical 6-[18F]Fluoro-L-DOPA ([18F]FDOPA) is a versatile positron emission tomography (PET) tracer used to image dopaminergic dysfunction in Parkinson’s disease, brain tumors, and neuroendocrine disorders. Despite its broad clinical applications, [18F]FDOPA production remains challenging. The electron-rich aromatic structure has traditionally necessitated electrophilic [18F]F2 labeling, resulting in low molar activity and potentially increasing the risk of pharmacological effects. Copper-mediated radiofluorination of organoboron precursors using nucleophilic [18F]fluoride provides a promising alternative but remains constrained by lengthy preparation time and high precursor consumption. Here, we developed a microscale copper-mediated radiosynthesis of [18F]FDOPA using a chip-based microreactor. Methods: A comprehensive set of reaction parameters, including type and amount of phase-transfer catalyst and base, solvent and additive composition, precursor and copper reagent quantity, concentration of deprotectant, and reaction temperature and time, was systematically evaluated using high-throughput microscale experiments. The optimized protocol was performed in a 10 μL reaction volume, followed by deprotection and purification using analytical radio-high-performance liquid chromatography (HPLC). Results: Starting from 0.03–1.54 GBq of [18F]fluoride, the optimized protocol afforded 0.02–0.83 GBq of [18F]FDOPA in a 25 min manually-operated synthesis (n = 16), corresponding to a radiochemical yield of 65 ± 2% and activity yield of 56 ± 2%. In contrast, a literature report of the conventionally-performed synthesis had a >4-fold longer preparation time and afforded 2.44 ± 0.70 GBq of product from 35–63 GBq starting activity, with an RCY of 10 ± 2% and activity yield of 5 ± 1%. Molar activity of the microscale synthesis was high (76–621 GBq μmol−1), and the product exhibited excellent radiochemical purity (>99%) and enantiomeric purity (100%). Conclusions: This microscale approach enables rapid, high-yield, and source-efficient production of [18F]FDOPA at quantities relevant for preclinical applications and supports further development toward future clinical translation.