Biologically active 11C-labeled amides using palladium-mediated reactions with aryl halides and [11C]carbon monoxide

Using [C-11]carbon monoxide in palladium-mediated synthesis, six amides were labeled with C-11. Phenyl and benzyl halides with halides as additional substituents were carbonylated and reacted with primary and secondary amines. Four of the selected amides were receptor ligands, one was a precursor to a receptor ligand, and one was a model compound. The C-11-labeled amides were obtained with good to almost quantitative radiochemical yields with specific activities up to 1000 GBq/mu mol. The radiochemical purity of the final products exceeded 98%. In one case, the corresponding C-13- substituted compound was produced to verify the position of the label. In a typical experiment starting with 5.0 GBq of [C-11]carbon monoxide, 2.2 GBq of LC-purified N-(2-aminoethyl)-4-chloro-[carbonyl-C-11]benzamide was obtained within 15 min from the start of the carbonylation reaction (74% decay-corrected radiochemical yield). The presented approach gives significant new possibilities for C-11-labeling and is seen to be valuable also for synthesis of C-13- and C-14-substituted compounds.