Synthesis of [(11)C]Am80 via Novel Pd(0)-Mediated Rapid [(11)C]Carbonylation Using Arylboronate and [(11)C]Carbon Monoxide.

(11)C-labeled methylbenzoates [(11)C]4a-d were synthesized using Pd(0)-mediated rapid cross-coupling reactions employing [(11)C]carbon monoxide and arylboronic acid neopentyl glycol esters 3a-d under atmospheric pressure in methanol-dimethylformamide (MeOH-DMF), in radiochemical yields of 12 ± 5-26 ± 13% (decay-corrected based on [(11)C]O). The reaction conditions were highly favorable for the synthesis of [(11)C]Am80 ([(11)C]2) and [(11)C]methyl 4-((5,5,8,8-tetramethyl-5,6,7,8-tetrahydronaphthalen-2-yl)carbamoyl)benzoate ([(11)C]2-Me) using 4-(5,5-dimethyl-1,3,2-dioxaborinan-2-yl)-N-(5,5,8,8-tetramethyl-5,6,7,8-tetrahydronaphthalen-2-yl)benzamide (5), both of which produced a decay-corrected radiochemical yield (RCY) of 26 ± 13%, with >99% radiochemical purity and an average specific radioactivity of 44 GBq/μmol. The yields of [(11)C]4a, [(11)C]2-Me, and [(11)C]2 were improved by the use of a 2-fold excess of the solvents and reagents under the same conditions to give respective yields of 66 ± 8, 65 ± 7, and 48 ± 2%.