Improved Stability and Practicality for Synthesis of 4-Borono-2-[(18)F]fluoro-l-phenylalanine by Combination of [(18)O]O(2) Single-Use and [(18)F]CH(3)COOF Labeling Agents

PURPOSE: 4-Borono-2-[(18)F]fluoro-l-phenylalanine ([(18)F]FBPA) synthesized with [(18)F]F(2), produced using the (18)O(p, n)(18)F reaction, has been reported for increasing radioactivity. However, a dedicated system and complex procedure is required to reuse the costly [(18)O]O(2) gas; also, the use of [(18)F]F(2) as a labeling agent reduces the labeling rate and radiochemical purity. We developed a stable and practical method for [(18)F]FBPA synthesis by combining [(18)F]F(2), produced using a [(18)O]O(2) single-use system, and a [(18)F]CH(3)COOF labeling agent. METHODS: The produced [(18)F]F(2) was optimized, and then [(18)F]FBPA was synthesized. For passivation of the target box, 0.5% F(2) was pre-irradiated in argon. Gaseous products were discarded; the target box was filled with [(18)O]O(2) gas, and then irradiated (first irradiation). Then, the [(18)O]O(2) gas was discarded, 0.05–0.08% F(2) in argon was fed into the target box, and it was again irradiated (second irradiation). The [(18)F]F(2) obtained after this was passed through a CH(3)COONa column, converting it into the [(18)F]CH(3)COOF labeling agent, which was then used for [(18)F]FBPA synthesis. RESULTS: The mean amount of as-obtained [(18)F]F(2) was 55.0 ± 3.3 GBq and that of as-obtained [(18)F]CH(3)COOF was 21.6 ± 1.4 GBq after the bombardment. The radioactivity and the radiochemical yield based on [(18)F]F(2) of [(18)F]FBPA were 4.72 ± 0.34 GBq and 12.2 ± 0.1%, respectively. The radiochemical purity and molar activity were 99.3 ± 0.1% and 231 ± 22 GBq/mmol, respectively. CONCLUSION: We developed a method for [(18)F]FBPA production, which is more stable and practical compared with the method using [(18)O]O(2) gas-recycling and [(18)F]F(2) labeling agent.