Precursor synthesis and radiolabelling of the dopamine D2 receptor ligand [11C]raclopride from [11C]methyl triflate

Desmethyl-raclopride was synthesized via a straightforward, three-step synthetic approach and used for the preparation of [C-11]raclopride from [C-11]methy] triflate. Conditions for the radiolabelling were optimized to obtain a simple and reproducible procedure suitable for automation. [C-11]Raclopride was prepared with an average radiochemical yield of 55-65% (decay corrected, based on starting [C-11]methyl triflate) in a total synthesis time (including purification and formulation of product) of 35 min. The radiolabelling procedure used significantly less precursor, avoided the use of DMSO, and was shorter compared to the standard radiolabelling procedure with [C-11]methyl iodide.