Synthesis of two dopamine D4 receptor ligands:11C labelled chromeno[3,4-c]pyridin-5-ones

The synthesis of two 11C labelled chromeno[3,4-c]pyridin-5-ones for the visualisation of the dopamine D4 receptor subtype has been developed. The production entailed an O-methylation of the O-desmethyl precursor with [11C]iodomethane in the presence of tetrabutylammonium hydroxide. Subsequent purification by RP-HPLC and formulation by tracer enrichment on a C18 Sep Pak provided a solution which was suitable for human iv injection. Specific activity of the tracer averaged 37 GBq/μmol at EOS and the radiochemical yields were 65% (decay-corrected, based on [11C]CH3I). Total activity obtained was 5·6–7·4 GBq. The preparations have been demonstrated to be chemically and radiochemically pure by HPLC.