Automated synthesis of 18F-Fluorocholine with synthesis module TRACERLAB(fx)FDG

Objectives Our goal is to demonstrate the feasibility, with acceptable marking yields, of the synthesis of ¹⁸Fluorometilcholine, [¹⁸F]-FCH, on a commercial synthesis module, the Tracerlab_FXFDG (General Electric), and the subsequent optimization of the synthesis process.

Methods The synthesis of the [¹⁸F]-FCH experienced, consists of two steps: first one provides alkylating agent, Fluoromethyl-bromide(¹⁸F-FCH₂Br); second step consist in the alkylation of the tertiary amine, such as N,N-dimethylaminoethanol. The most difficult step is the formation of ¹⁸FCH₂Br, taking place by nucleophilic substitution of CH₂Br₂ with ¹⁸F previously anidrificated by two evaporation steps in presence of K2.2.2. in anhydrous acetonitrile. This intermediate is, in normal conditions, a gas, with a boiling point of 19°C, which makes it difficult to isolate for the next step. Purification is made through four silica gel Sep-Pak cartridges placed in series. The problems we had were due mainly to the reaction vessel size, which is affecting the first synthesis step. ¹⁸F-CH₂Br obtained passes trough a C18 cartridge, previously loaded with N,N-dimethylaminoethanol.

Results The production yield of ¹⁸F-CH₂Br starting with ¹⁸F is 35-40% and the yield for [¹⁸F]-FCH is 15-20%. The radiochemical purity, determined by HPLC, is ≥ 98%.

Conclusions Synthesis presents an acceptable yeald, and the entire process has been implemented on an commercial automatic synthesis module for regular productions.