Objective: The aim of this study was to establish a reliable and routine method for the preparation of 4-[10B]borono-2-[18F]fluoro-L-phenylalanine (L-[18F]FBPA) for boron neutron capture therapy-oriented diagnosis using positron emission tomography.
Methods: To produce L-[18F]FBPA by electrophilic fluorination of 4-[10B]borono-L-phenylalanine (L-BPA) with [18F]acetylhypofluorite ([18F]AcOF) via [18F]F2 derived from the 20Ne(d,α)18F nuclear reaction, several preparation parameters and characteristics of L-[18F]FBPA were investigated, including: pre-irradiation for [18F]F2 production, the carrier F2 content in the Ne target, L-BPA-to-F2 ratios, separation with high-performance liquid chromatography (HPLC) using 10 different eluents, enantiomeric purity, and residual trifluoroacetic acid used as the reaction solvent by gas chromatography-mass spectrometry.
Results: The activity yields and molar activities of L-[18F]FBPA (n = 38) were 1200 ± 160 MBq and 46-113 GBq/mmol, respectively, after deuteron-irradiation for 2 h. Two 5 min pre-irradiations prior to [18F]F2 production for 18F-labeling were preferable. For L-[18F]FBPA synthesis, 0.15-0.2% of carrier F2 in Ne and L-BPA-to-F2 ratios > 2 were preferable. HPLC separations with five of the 10 eluents provided injectable L-[18F]FBPA without any further formulation processing, which resulted in a synthesis time of 32 min. Among the five eluents, 1 mM phosphate-buffered saline was the eluent of choice. The L-[18F]FBPA injection was sterile and pyrogen-free, and contained very small amounts of D-enantiomer (< 0.1% of L-[18F]FBPA), L-BPA (< 1% of L-FBPA), and trifluoroacetic acid (< 0.5 ppm).
Conclusions: L-[18F]FBPA injection was reliably prepared by the electrophilic fluorination of L-BPA with [18F]AcOF followed by HPLC separation with 1 mM phosphate-buffered saline.
Keywords: BNCT; L-[18F]FBPA; PET; Quality control; [18F]F2 production.