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Facile [¹¹C]PIB synthesis using an on-cartridge methylation and purification showed higher specific activity than conventional method using loop and HPLC purification

Yong-Seok Lee, Jae Min Jeong^*,Yong-Hyun Cho, Jae-Hyung Lee, Hong-Jae Lee

Jin-Eui Kim, Yun-Sang Lee, Keon-Wook Kang,

PET center, Department of Nuclear Medicine, Seoul National University Hospital, Seoul, Korea

Purpose: [¹¹C]PIB synthesis has been performed by a loop-methylation and HPLC purification in our lab. However, this method is time-consuming and requires complicated systems. Thus, we developed an on-cartridge method which simplified the synthetic procedure and reduced time greatly by removing HPLC purification step. We compared 6 different cartridges (C18, tC18, tC18 environmental, alumina, HLB, CM) and evaluated the [¹¹C]PIB production yields and specific activities.

Materials and Methods: The cartridges were prewashed with 5 mL EtOH amd purged with nitrogen gas. Precursor (1 mg 6-OH-BTA-0, ABX, Germany) in 100 µL of cyclohexanone was loaded each cartridge. [¹¹C]MeOTf was synthesized by using TRACERlab FXC Pro (GEMS, Sweden) and was transferred into the cartridge by blowing with helium gas for 3 min at room temperature. To remove byproducts and impurities, cartridges were washed out by 20 mL of 30 % EtOH in 0.5 M NaH₂PO₄ solution (pH 4.5) and 10 mL of distilled water. And then, [¹¹C]PIB was eluted by 5 mL of 30 % EtOH in 0.5 M NaH₂PO₄ into the collecting vial containing 10 mL saline.

Results: Among the 6 cartridges, only tC18 environmental cartridge could remove impurities and byproducts from [¹¹C]PIB completely and showed higher specific activity than traditional HPLC purification method. This method took only 8 ~ 9 min from methylation to formulation. For the tC18 environmental cartridge and conventional HPLC loop methods, the radiochemical yields (EOS) were 12.3 2.2% and 13.9 4.4%, respectively, and the specific activities were 420.6 20.4 GBq/µmol (n=3) and 78.7 39.7 GBq/µmol (n=41), respectively.

Conclusion: We successfully developed a facile on-cartridge methylation method for [¹¹C]PIB synthesis which enabled the procedure more simple and rapid, and showed higher specific activity than HPLC purification method.