Synthesis of [11C]- and (13C)-Cyanogen Bromide, Useful Electrophilic Labelling Precursors.

Abstract

A fast and simple route to the synthesis of {[}C-11]- and (C-13)-cyanogen bromide has been developed. Hydrogen {[}C-11]cyanide was produced on-line from {[}C-11] carbon dioxide and reacted with bromide in triethyleneglycol dimethyl ether to give a 70-80% decay-corrected radiochemical yield of {[}C-11]cyanogen bromide in 9-11 min, counted from the end of the bombardment. In a typical run, starting from 20.5 GBq (550 mCi) {[}C-11]carbon dioxide, 10.1 GBq (274 mCi) {[}C-11]cyanogen bromide were obtained. The {[}C-11]cyanogen bromide was transferred to a reaction vessel in a stream of nitrogen gas and used in the synthesis of phenyl {[}C-11]cyanate (1a), 4-nitrophenyl {[}C-11]cyanate (1b), 2,4-dinitrophenyl {[}C-11]cyanate (1c), diethyl{[}C-11]cyanamide (2a), phenyl{[}C-11]cyanamide (2b), diphenyl{[}C-11]cyanamide (2c), 1-({[}C-11]cyano)-4-(dimethylamino)pyridinium bromide (2d), and benzyl {[}C-11]thiocyanate (3a). Compounds 1-3 were obtained with radiochemical yields of 54-98% in 13-27 min counted from {[}C-11]cyanogen bromide. Phenyl {[}C-11]thiocyanate (3b), was obtained in a 12% radiochemical yield. Using the procedure for benzyl {[}C-11]thiocyanate (3a), benzyl (C-13)thiocyanate was obtained in 71 % yield.