One pot synthesis of [18F]-Fluoroethylcholine

Objectives [F18]-fluoroethylcholine (FECH) is widely used as PET tracer for prostate cancer. Usually a two step synthesis with an intermediate cleaning step for the formed [18F]-fluorethyltosylate is used. A one pot synthesis was published by Pascali et al..The aim of this study was to optimize and develop an easy one pot synthesis combined with a cleaning procedure based on standard cartridges.

Methods FECH was prepared by a [18F]-fluorethylation of 2-dimethylaminoethanol (DMAE). [F18]Fluoride was produced by the ¹⁸O(p,n)¹⁸F nuclear reaction with a 11 MeV proton beam. The [18F]-fluoride was collected on an AG1X8 column and eluted with 0.4 mL potassium carbonate into the first reactor filled with 20 mg Kryptofix 2.2.2 (Merck) and 1.0 mL acetonitrile. The solvent was evaporated under a stream of helium at 90°C and reduced pressure. After addition of 15 mg ethylene glycol-1,2-ditosylate in 1.0 mL acetonitrile the reaction mixture was heated 6 min at 90°C, the solvents evaporated under a stream of helium at 90°C and reduced pressure. 0.3 mL DMAE were added and the reaction mixture was heated at 120°C for 4 minutes. The product mixture was diluted with 4.0 mL ethanol and the formed FECH was cleaned with an unconditioned t-C18 cartridge and collected on an also unconditioned CM cartridge. Both cartridges were washed with 4.0 mL ethanol. Then the CM cartridge was rinsed with 10 mL water and the final product was eluted with 10 mL saline solution (0.9 %), cleaned with a t-C18 and a C18 environmental cartridge (conditioned with 10 mL ethanol and 10 mL water) and finally sterile filtered.

Results The synthesis is finished after 35 min. Starting with 36 GBq [18F]-fluoride, the synthesis typically yielded 17 GBq (47 ± 5 %) [18F]-FECH (n.d.c.). The radiochemical purity was higher then 97%.

Conclusions The optimized reaction temperature and the use of the t-C18/C18 cartridges for the final cleaning step leads to a synthesis of FECH in a high yield