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).