Facile and improved synthesis of [11C]Me‐QNB

¹¹C]Me‐QNB is a muscarinic acetylcholinergic receptor antagonist that has been used for the assessment of myocardial muscarinic receptors density in different cardiovascular pathologies. In the current technical note, we report a facile, highly efficient and fully automated method for the preparation of this radiotracer. The radiosynthesis was performed by reaction of ¹¹C]CH₃I with the desmethylated precursor (QNB) at room temperature using the captive solvent method. Excellent radiochemical yield (91.1 ± 2.4%, decay‐corrected) and radiochemical purity (>99.5%), and good specific activity (137 ± 5 GBq/µmol) were obtained when the purification was performed by reverse phase HPLC in overall synthesis time <31 min. Purification using solid‐phase extraction offered lower radiochemical yield (27.6 ± 3.1%, decay‐corrected) and radiochemical purity (>95%) but higher specific activity (244 ± 18 GBq/µmol) in shorter reaction times (<21 min). These results, especially concerning radiochemical yield, significantly improve those previously reported in which the reaction was performed in a vial and the purification step was based on ionic chromatography.