Radiochemical synthesis of [123I]2-iodo-lisuride for dopamine D2-receptor studies

By variation of reaction parameters iodination of 3-(9-10-didehydro-6-methyl-8α-ergolinyl)-1,1-diethylurea (lusuride) was performed with the radiohalogen [123I]iodine (t(1(2)) = 13.3 h). For comparative experiments and stability studies the β--emitting radioisotope [131I]iodine (t(1(2)) = 8.04 d) was also used. Reaction occurs at the activated position 2 of the molecule, thus leading to [123I]3-(9,10-didehydro-2-iodo-6-methyl-8α-ergolinyl)-1,1- diethylurea([123I]2-iodo-lisuride, [123I]ILIS) or the analogous [131I]iodine-labeled compound, respectively. Electrophilic radioactive species were generated by oxidation of no-carrier-added (n.c.a.) iodide with IODOGEN (1,3,4,6-tetrachloro-3α,6α-diphenylglycouril) fixed on the glass wall of the reaction vial prior to iodination. After optimization of reaction parameters [123I]2-iodo-lisuride after HPLC-purification was obtained with radiochemical yields of 70 ± 5% and a radiochemical purity of >97%. In n.c.a. syntheses, specific activities of the product were in the range between 4440 and 7400 GBq/μmol (120-200 Ci/μmol) corresponding to 50-85% of the theoretical value.