Automated GMP production and long-term experience in radiosynthesis of CB<sub>1</sub> tracer [<sup>18</sup> F]FMPEP-<i>d</i> <sub>2</sub>
Here, we describe the development of an in-house-built device for the fully automated multistep synthesis of the cannabinoid CB1 receptor imaging tracer (3R,5R)-5-(3-([18F]fluoromethoxy-d2)phenyl)-3-(((R)-1-phenylethyl)amino)-1-(4-(trifluoromethyl)phenyl)pyrrolidin-2-one ([18F]FMPEP-d2), following good manufacturing practices. The device is interfaced to a HPLC and a sterile filtration unit in a clean room hot cell. The synthesis involves the nucleophilic 18F-fluorination of an alkylating agent and its GC purification, the subsequent 18F-fluoroalkylation of a precursor molecule, the semipreparative HPLC purification of the 18F-fluoroalkylated product, and its formulation for injection. We have optimized the duration and temperature of the 18F-fluoroalkylation reaction and addressed the radiochemical stability of the formulated product. During the past 5 years (2013–2018), we have performed a total of 149 syntheses for clinical use with a 90% success rate. The activity yield of the formulated product has been 1.0 ± 0.4 GBq starting from 11 ± 2 GBq and the molar activity 600 ± 300 GBq/μmol at the end of synthesis.