Synthesis of [11C]palmitic acid for PET imaging using a single molecular sieve 13X cartridge for reagent trapping, radiolabeling and selective purification

Introduction: Radiolabeled fatty acids are valuable metabolic tracers for PET imaging. Carbon-11 is widely used in clinical PET studies due to the prevalence of facile techniques enabling the incorporation of [C-11]CO2 and [C-11]CH3 into molecules and a short half-life (20.4 min) that translates into low patient dose. However, the short half-life considerably limits the time for radiosynthesis. Furthermore, the majority of the syntheses of [C-11]palmitic acid in common use employ high starting [C-11]CO2 activities and/or expensive equipment. Methods: [C-11]CO2 was trapped with greater than 99.99% efficiency by a three stage cartridge packed with molecular sieve 13X, 100-120 mesh. The labeling of n-pentadecylmagnesium bromide took place in 5 min in the cartridge, and the [C-11]palmitic acid product was selectively eluted in ethanol following alkaline and acidic washes of the column. Results: The system reliably produced more than 925 MBq (25 mCi) of [C-11]palmitic acid suitable for human use from 7.4 GBq (200 mCi) of [C-11]CO2 in 8 min from end-of-bombardment. Conclusions: We have exploited the properties of the inexpensive molecular sieve 13X to develop a miniature, disposable and leak tight "gas capture" system for the rapid labeling and purification of [C-11]fatty acids in good yield and >99% radiochemical purity. The rapidity of the synthesis and purification allows small [C-11]CO2 starting activities to be used, and with no requirement for expensive synthesis equipment or facilities, the system can be implemented in any radiopharmaceutical center. (C) 2015 Elsevier Inc. All rights reserved.