Synthesis of a radiotracer for studying σ receptors in vivo using PET: (+)‐N‐[¹¹C]‐benzyl‐N‐normetazocine (1S, 5S,9S‐(+)‐cis‐2‐[¹¹C]‐2′‐hydroxy‐5,9‐dimethyl‐6,7‐benzomorphan)

(+)‐N‐[¹¹C]‐Benzyl‐N‐normetazocine (1S,5S,9S‐(+)‐cis‐2‐[¹¹C]‐benzyl‐2′‐hydroxy‐5,9‐dimethyl‐6,7‐benzomorphan), a potent and selective ligand for the σ receptor, was prepared by N‐benzylation of (+)‐cis‐N‐normetazocine with [α‐¹¹C]‐benzyl iodide in ethanol using sodium hydrogen carbonate as the proton acceptor. The radiotracer was purified by semi‐preparative reverse‐phase HPLC. The average specific activity was 746 mCi/μmol calculated at end‐of‐synthesis (EOS). The average time of synthesis including formulation was 35 minutes.