An updated synthesis of [11C]carfentanil for positron emission tomography (PET) imaging of the μ-opioid receptor

[C-11]Carfentanil ([C-11]CFN) is a selective radiotracer for in vivo positron emission tomography imaging studies of the -opioid system that, in our laboratories, is synthesized by methylation of the corresponding carboxylate precursor with [C-11]MeOTf, and purified using a C2 solid-phase extraction cartridge. Changes in the commercial availability of common C2 cartridges have necessitated future proofing the synthesis of [C-11]CFN to maintain reliable delivery of the radiotracer for clinical imaging studies. An updated synthesis of [C-11]CFN is reported that replaces a now obsolete purification cartridge with a new commercially available version and also substitutes the organic solvents used in traditional production methods with ethanol.