Metabolism of the PET ligand [11C]SCH 23390. Identification of two radiolabelled metabolites with HPLC

¹¹C]SCH 23390 is a radioligand used for PET determination of the D₁-dopamine receptor in the living human brain. An HPLC procedure was developed for analysis of ¹¹C]SCH 23390 and its radiolabelled metabolites in plasma after injection of the radioligand into human subjects in realtion to PET studies. After i.v. injection ¹¹C]SCH 23390 rapidly declined from plasma, about 50 per cent of the radioligand remaining unchanged after 4 min and about 10 per cent after 40 min. The decline followed a biexponential time course. Two of the probable metabolites, the O-sulphate and the O-glucuronide of SCH 23390 were synthesized and characterized. Two radioactive substances in plasma co-migrated with these reference compounds.