One-step high-radiochemical-yield synthesis of [18F]FP-CIT using a protic solvent system

Sang Ju Lee, Seung Jun Oh, Dae Yoon Chi, Se Hun Kang, Hee Seup Kil, Jae Seung Kim, Dae Hyuk Moon
Nuclear Medicine and Biology 2007, 34 (4): 345-51
Although [18F] fluoropropylcarbomethoxyiodophenylnortropane (FP-CIT) is a promising radiopharmaceutical for dopamine transporter imaging, it has not been used for clinical studies because of low radiochemical yield. The purpose of our study was to develop a new radiochemistry method using a protic solvent system to obtain a high radiochemical yield of [18F]FP-CIT in single-step manual and automatic preparation procedures. [18F]F(-) was trapped on a QMA Sep-Pak cartridge or PS-HCO(3) cartridge and eluted with Cs2CO(3)/K222 buffer or TBAHCO3 respectively, or 8 microl of TBAOH was added directly to [18F]F(-)/H(2)(18)O solution in a reactor without using a cartridge. After drying, 18F] fluorination was performed with 2-6 mg of mesylate precursor, 100 microl of CH(3)CN and 500 microl of t-BuOH at 50-120 degrees C for 5-30 min, followed by high-performance liquid chromatography (HPLC) purification to obtain the final product. For comparison, the same procedure was performed with a tosylate precursor. Manual synthesis gave a decay-corrected radiochemical yield of 52.2+/-4.5%, and optimal synthesis conditions were as follows: TBAOH addition, 4 mg of precursor, 100 degrees C and 20 min of [18F] fluorination (n=3). We obtained low radiochemical yields of [18F]FP-CIT with carbonate elution systems such as Cs2CO(3) or TBAHCO3. We also developed an automatic synthesis method based on manual synthesis results. In automatic production, we obtained a decay-corrected radiochemical yield of 35.8+/-5.2% after HPLC purification, and we did not have any synthesis failures (n=14). Here, we describe our new method for the synthesis of [18F]FP-CIT using a protic solvent system. This method gave a high radiochemical yield with high reproducibility and might enable [18F]FP-CIT to be used clinically and commercially.

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