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

By variation of reaction parameters iodination of 3-(9,10-didehydro-6-methyl-8 alpha-ergolinyl)-1,1-diethylurea (lisuride) was performed with the radiohalogen [I-123]iodine (t(1/2) = 13.3 h). For comparative experiments and stability studies the beta(-)emitting radioisotope [I-131]iodine (t(1/2) = 8.04 d) was also used. Reaction occurs at the activated position 2 of the molecule, thus leading to [I-123]3-(9,10-didehydro-2-iodo-6-methyl-8 alpha-ergolinyl)-1, 1-diethylurea ([I-123]2-iodo-lisuride, [I-123]ILIS) Or the analogous [I-131]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-tett-achloro-3 alpha,6 alpha-diphenylglycouril) fixed on the glass wall of the reaction vial prior to iodination, After optimization of reaction parameters [I-123]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/mu mol (120-200 Ci/mu mol) corresponding to 50-85% of the theoretical value.