High-yield automated synthesis of [18F]fluoroazomycin arabinoside ([18F]FAZA) for hypoxia-specific tumor imaging

The aim of this study was to develop an efficient fully automated synthesis method to achieve a high radiochemical yield of [18F]FAZA with a small amount of precursor. A small cartridge containing 25 mg of the QMA resin was prepared and evaluated to obtain [18F]F− in a small quantity of base (K2CO3), which might allow the use of a small amount of precursor. The labeling and hydrolyzing conditions for [18F]FAZA synthesis were also investigated manually. No-carrier-added [18F]F− was trapped on the small QMA cartridge and eluted with a mixture of Krytofix 222 (2.26 mg, 6.0 μmol) and K2CO3 (0.69 mg, 5.0 μmol) in 70% MeCN (0.4 mL). The automated synthesis of [18F]FAZA was optimally performed with a modified NIRS original synthesis system for clinical use, by labeling 2.5 mg (5.2 μmol) of the precursor in DMSO (0.4 mL) at 120 °C for 10 min, and then by hydrolyzing the 18F-labeled intermediate with 0.1 M NaOH (0.5 mL) at room temperature for 3 min. Using the above condition, the [18F]FAZA injection was obtained with a high radiochemical yield of 52.4±5.3% (decay-corrected, n=8) within 50.5±1.5 min.