Successful application of a neutral organic base, 1,8-bis(tetramethylguanidino)naphthalene (TMGN), for the radiosynthesis of [11C]raclopride

[11C]Raclopride is one of the most popular PET tracers used in Parkinson's disease studies. We previously prepared [11C]raclopride with reasonable yields using NaOH as an inorganic base, but the reaction patterns fluctuated. In this study, we describe the successful application of a commercially available 'super basic' proton sponge, TMGN, as a base for the [11C]methylation step using [11C]CH3OTf. This novel TMGN method produced better radiochemical yields, as well as enhanced reproducibility and a reduction in side products. Under optimal conditions (1.2 equiv. of TMGN), the radiochemical yield was 14.4±0.2% (ndc, EOS, n=5) and the specific activity was 66.6±13.3 GBq/mmol (n=5).