Authors: Noora Rajala, Salla Lahdenpohja, Olof Solin and Anna K. Kirjavainen
Radiopharmaceutical Chemistry Laboratory, Turku PET Centre, University of Turku, Turku, Finland
Background
Transition metal mediated 18F-fluorination have been widely studied and the most recently published approach is ruthenium-mediated 18F-deoxyfluorination.[1]
Aims
We applied Ru- mediated 18F-deoxyfluorination to produce a new cannabinoid subtype 1 specific radiotracer [18F]FPATPP ((3R,5R)-5-(3-[18F]fluorophenyl)-3-(((R)-1‑phenylethyl)amino)-1-(4-(trifluoromethyl)phenyl)pyrrolidin-2-one). Our aim was to optimise the synthesis conditions and we utilised solid phase extraction (SPE) or azeotropic distillation for [18F]fluoride activation.
Methods
Previously described Ru-mediated labelling method (Fig. 1) was followed[1]. In the SPE method, Ru-phenol complex was used to elute [18F]fluoride from an anion exchange cartridge. The subsequent reaction was conducted at 100°C to 160°C for 10 to 30 min. In the azeotropic distillation method, subsequent reaction was conducted at 160°C.
Results and Conclusion
The optimised conditions for the radiofluorination were 30 min in 160 °C by using SPE method for [18F]fluoride activation. At 100°C no reaction occurred. Increasing the temperature from 130°C to 160°C increased the radiochemical yield of [18F]FPATPP from 20 to 50% (based on HPLC analysis of crude reaction mixture).
References
1. Beyzavi MH et al. 18F-Deoxyfluorination of Phenols via Ru π-Complexes, ACS Cent. Sci. 2017;3(9):944-948.