Direct fixation of [C-11]-CO2 by amines: formation of [C-11-carbonyl]-methylcarbamates

[C-11-Carbonyl]-methylcarbamates can be synthesised directly from [C-11]-CO2 and primary or secondary amines in a one-pot, two-step reaction. The use of either diazabicyclo[5.4.0] undec-7-ene (DBU) or 2-tert-butylimino-2-diethylamino-1,3-dimethyl-perhydro-1,3,2-diazaphosphorine (BEMP) enables efficient trapping of [C-11]-CO2 in small volumes of DMF as [C-11]-carbamate salts. Subsequent reaction with a variety of methylating agents rapidly generates the desired [C-11-carbonyl]-methylcarbamates in high radiochemical yields. The usefulness of the method is illustrated by the efficient radiosynthesis of a kappa opioid receptor imaging radiotracer, useful in positron emission tomography (PET).