Automated one‐step radiosynthesis of the CB 1 receptor imaging agent [ 18 F]MK‐9470

The fluorine‐18‐labeled positron emission tomography (PET) radiotracer [ 18 F]MK‐9470 is a selective, high affinity inverse agonist that has been used to image the cannabinoid receptor type 1 in human brain in healthy and disease states. This report describes a simplified, one‐step [ 18 F]radiofluorination approach using a GE TRACERlab FX FN module for the routine production of this tracer. The one‐step synthesis, by [ 18 F]fluoride displacement of a primary tosylate precursor, gives a six‐fold increase in yield over the previous two‐step method employing O ‐alkylation of a phenol precursor with 1,2‐[ 18 F]fluorobromoethane. The average radiochemical yield of [ 18 F]MK‐9470 using the one‐step method was 30.3 ± 11.7% ( n  = 12), with specific activity in excess of 6 Ci/µmol and radiochemical purity of 97.2 ± 1.5% ( n  = 12), in less than 60 min. This simplified, high yielding, automated process was validated for routine GMP production of [ 18 F]MK‐9470 for clinical studies.