Simultaneous tritium labelling of two potent 5-HT4 ligands.

Two potent and selective 5-HT(4) ligands, [(3)H]-5-[(N-propylpiperidin-4-yl)methoxy]-1,2,3,4-tetrahydrobenzo[h][1,6] naphthyridine (1a) and [(3)H]-1-methyl-5-[(N-propylpiperidin-4-yl)methoxy]pyrrolo[1,2-a]thieno[2,3-e]pyrazine (2a) were radiolabelled with tritium. Radioactive labelling was achieved by simultaneous tritium reduction of a mixture of both propargylic precursors (1c-2c). The two tritiated ligands thus obtained were radiochemically pure and possessed high radioactive specific activities. These tritiated 5-HT(4) ligands will allow for binding characterization as an essential tool for their further development.