Aryl triflates and [11C]/(13C)carbon monoxide in the synthesis of 11C-/13C-amides

Palladium(0)-mediated carbonylation reactions using aryl triflates, amines, and a low concentration of [C-11]carbon monoxide were used in the syntheses of 13 C-11-labeled amides. Lithium bromide was used as an additive to facilitate the reaction. The C-11-labeled products were obtained with decay-corrected radiochemical yields in the range of 2-63%. The radiochemical purity of the final products exceeded 98%. As an example, a reaction starting with 1.79 GBq [C-11]carbon monoxide gave 0.38 GBq of LC-purified N-isopropyl-4-nitro-[C-11]benzamide within 27 min from the start of the carbonylation reaction (54% decay-corrected radiochemical yield). The specific radioactivity of this compound was 191 GBq/mumol, 35 min after the end of a 10 muAh bombardment. N-Benzylisoquinoline-1-(C-13)carboxamide was prepared and analyzed by NMR for confirmation of the labeling position. The triflates 16, 20, 21, and 22 were synthesized from the corresponding alcohols and trifluoromethanesulfonic anhydride. The reference compounds 30a and 30b were prepared from the corresponding carboxylic acids and benzylamine. The other nine reference compounds 32a to 32i were synthesized from the respective acid chlorides and amines. The presented report shows that the sometimes more easily obtainable aryl triflates can be a useful alternative to the commonly used aryl halides in palladium(0)-mediated synthesis of C-11/C-13-amides.