Using [ 11 C]carbon monoxide in palladium-mediated synthesis, six amides were labeled with 11 C. 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 11 C-labeled amides were obtained with good to almost quantitative radiochemical yields with specific activities up to 1000 GBq/μmol. The radiochemical purity of the final products exceeded 98%. In one case, the corresponding 13 C-substituted compound was produced to verify the position of the label. In a typical experiment starting with 5.0 GBq of [ 11 C]carbon monoxide, 2.2 GBq of LC-purified N -(2-aminoethyl)-4-chloro[carbonyl- 11 C]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 11 C-labeling and is seen to be valuable also for synthesis of 13 C- and 14 C-substituted compounds.
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Kihlberg et al. (1999) studied this question.