A simple loop method for the automated preparation of [11C]raclopride from [11C]methyl triflate

A simple automated preparation of [11C]raclopride by reaction of [11C]methyl triflate with demethylraclopride triflate is described. The conventional bubbling of [11C]methyl triflate into the precursor solution was compared with two alternative methods which used a commercially available C18 cartridge (on-column method) or an empty PTFE tube (loop method) as support for the precursor solution. The influence of several solvents was assessed for all three methods. The on-column method showed excellent trapping efficiencies of [11C]methyl triflate but gave the lowest radiochemical yields. The loop method proved to be a simplified alternative to the bubbling method, giving comparable radiochemical yields with less precursor and offering an easy way to transfer the reaction mixture into an HPLC column. By the simple-loop method [11C]raclopride could be prepared in over 40% radiochemical yields (decay-corrected and based on [11C]methyl triflate).