4.2.3. Radiolabeling of 18F-FPABZA (3a) and 18F-FNABZA (3b)

Aqueous ¹⁸F-HF was produced by SCANDITRONIX cyclotron using ¹⁸O (p,n) ¹⁸F reaction and kindly provided by Taipei Veterans General Hospital (Taipei, Taiwan). ¹⁸F-HF was loaded into a Plus QMA Sep-Pak cartridge (Waters) pre-conditioned with 10 mL of 0.5 M K₂CO₃ and 10 mL of ddH₂O. The radioactivity-trapped QMA cartridge was eluted with 0.8 mL of eluent (15 mg of kryptofix 2.2.2 and 3 mg of K₂CO₃ in acetonitrile/H₂O = 4/1, v/v). The solvent was evaporated to dryness at 110 °C. To the reaction vial, 1 mL of anhydrous acetonitrile was added as azeotrope to remove residual water. The precursor (2a or 2b, 7.5 mg) dissolved in anhydrous dimethylformamide (1 mL) was added to the vial. The reaction mixture was reacted at 140 °C for 30 min. After cooling, the mixture was loaded into a Plus C18 Sep-Pak cartridge (Waters) pre-conditioned with 10 mL of methanol and 10 mL of ddH₂O. The cartridge was sequentially eluted with 80 mL of ddH₂O, 8 mL of 30% ethanol, and 3 mL of absolute ethanol. The collected final elution was evaporated to dryness and then re-dissolved in 5% ethanol, 5% tween 80, and 2% BSA in normal saline. The solution was filtered by a 0.22 μm filter to give the final product (¹⁸F-FPABZA or ¹⁸F-FNABZA).