Synthesis and radiolabelling of 2 beta-carbomethoxy-3 beta-(3 '-iodo-4 '-isopropylphenyl) nortropane as a radioligand for the exploration of the serotonin transporter by SPET.

In order to develop a potential tool for SPET examination of the serotonin transporter (5-HTT) in the human brain, we report the synthesis and radiola belling of 2 beta-carbomethoxy-3 beta-(3'-iodo-4'-isopropylphenyl) nortropa ne (LBT-44). We also report ex vivo autoradiography performed in the rat br ain. The radiosynthesis of [I-125]LBT-44 was accomplished by iododestannyla tion of a trimethyltin precursor using [I-125]sodium iodide and peracetic a cid or choramine-T as oxidant. After purification by reverse phase HPLC, [I -125]LBT-44 was obtained in a radiochemical yield higher than 75% and a rad iochemical purity greater than 95%. Ex vivo autoradiographic studies reveal ed a marked accumulation of [[I-125]LBT-44 in brain areas rich in 5-HTT whe reas no accumulation was observed in the striatum, which is rich in dopamin e transporters. These results are in favour of specific binding of [I-125]L BT-44 to 5-HTT that is required for SPET exploration in human.