Copper‐Mediated Radiofluorination of Aryl Pinacolboronate Esters: A Straightforward Protocol by Using Pyridinium Sulfonates

Abstract

Radiofluorination of arylboronic acids pinacol esters (arylBPin) mediated by copper triflate pyridine complex is one of the more promising synthetic approaches for the direct introduction of nucleophilic [18F]fluoride into non‐activated arenes and heteroarenes. However, the application of this method to the production of positron emission tomography (PET) radiotracers in automated synthesizers remains a challenging task. The choice of phase‐transfer catalyst (PTC) and corresponding base used for the generation of reactive [18F]fluoride species has a profound impact on the efficiency of the 18F‐fluorination process. Herein we report the development of a simple procedure involving trapping of the aqueous [18F]fluoride on a weak anion‐exchange resin (WAX) and its release by elution with pyridinium sulfonate in dimethyl acetamide. Obtained reactive [18F]fluoride was used as‐is in a copper‐catalyzed fluorination reaction employing pyridinium salt as both PTC and base. High radiochemical conversion rates (RCCs) achieved for a series of simple arylBPin substrates and 4‐[18F]fluoro‐D,L‐phenylalanine demonstrate the efficiency of this novel 18F‐processing approach. Notably, the proposed method obviates conventional azeotropic drying steps, solvents evaporation and/or changeover and can be implemented on commercial automated synthesizers.