Evaluation and improvement of CuI‐mediated ¹¹C‐cyanation

Abstract

CuI‐mediated 11C‐cyanation was evaluated by synthesizing [11C]perampanel ([11C]5) as a model compound and compared with previous reports. To a DMF solution with 5′‐(2‐bromophenyl)‐1′‐phenyl‐[2,3′‐bipyridin]‐6′(1′H)‐one (4) and CuI, [11C]NH4CN in a stream of ammonia/nitrogen (5:95, v/v) gas was bubbled. Subsequently, the reaction mixture was heated at 180°C for 5 min. After HPLC purification, [11C]5 was obtained in 7.2 ± 1.0% (n = 4) non‐decay corrected radiochemical yield with >99% radiochemical purity and a molar activity of 98 ± 28 GBq/μmol. In vivo evaluations of [11C]5 were performed using small animals. PET scans to check the kinetics of [11C]5 in the whole body of mice suggested that [11C]5 spreads rapidly into the brain, heart, and lungs and then accumulates in the small intestine. To evaluate the performance of CuI‐mediated 11C‐cyanation reaction, bromobenzene (6a) was selected as the model compound; however, it failed. Therefore, optimization of the reaction conditions has been performed, and consequently, the addition of K2CO3 and prolonging the reaction time improved the radiochemical yield about double. With this improved method, CuI‐mediated 11C‐cyanation of various (hetero)aromatic bromides was performed to exhibit the tolerance of most functional groups and to provide 11C‐cyanated products in good to moderate radiochemical yields.