Fully Automated Synthesis of Novel TSPO PET Imaging Ligand [F]Fluoroethyltemazepam.

Introduction: Benzodiazepines, including temazepam are described as TSPO antagonists. In fact, TSPO was initially described as a peripheral benzodiazepine receptor (PBR) with a secondary binding site for diazepam. TSPO is a potential imaging target of neuroinflammation because there is an amplification of the expression of this receptor.

Objectives: Herein, we developed a novel fluorinated benzodiazepine ligand, [F]Fluoroethyltemazepam ([F]F-FETEM), for positron emission tomography (PET) imaging of translocator protein (18 kDa).

Methods: [F]F-FETEM was radiolabelled with an automated synthesizer via a one-pot procedure. We conducted a [F]F-aliphatic nucleophilic substitution of a tosylated precursor followed by purification on C18 and Alumina N SPE cartridges. Quality control tests was also carried out.

Results: We obtained 2.0-3.0% decay-uncorrected radiochemical activity yield (3.7% decay-corrected) within the whole synthesis time about 33 min. The radiochemical purity of [F]F-FETEM was over 90% by TLC analysis.

Conclusions: This automated procedure may be used as basis for future production of [F]F-FETEM for preclinical PET imaging studies.