Synthesis of 3H‐ and 14C‐ketanserin

Ketanserin, 3-[2-[4-(4-fluorobenzoyl)-1-piperidinyl]ethyl]-2,4(1H,3H)-quinazol-inedione is a new serotonin S2-receptor blocking agent used in hypertension and related diseases. Pharmacokinetic studies required the synthesis of monolabelled 3H- and 14C-ketanserin tartrate. The tritium compound had the label placed at the fluorobenzoyl moiety, whereas for 14C-ketanserin the heterocyclic part of the quinazolinedione system was chosen. Receptor binding studies and application in radioimmunoassay necessitated the synthesis of a molecule at higher specific activity, hence a dilabelled molecule was constructed with tritium atoms placed at opposite positions in the molecule. The title compounds were obtained at specific activities of 169.5, 5.66 and 34900 mCi/mmol, respectively and with HPLC purities of > 98%.