SYNTHESIS OF [I-123] -METHYL-1-PHENYL-1,3,8-TRIAZASPIRO[4.5]DECAN-4-ONE - A POTENTIAL DOPAMINE-D-2 RECEPTOR RADIOLIGAND FOR SPECT

3]-8-[4-[2-(5-Iodothienyl)]-4-oxobutyl]-3-methyl-1 phenyl-1,3,8-triaza spiro[4.5]-decan-4-one ((1) under bar)) has been synthesized as a pote ntial ligand for dopamine D-2 receptors. This new compound proved to b e moderate in lipophilicity (log P = 3.14) and exhibited high affinity (Ki = 1.9 nM) for the dopamine D-2 receptor as well as good selectivi ty for D-2 versus serotonin 5HT(2) receptors (Ki 5HT(2)/D-2 = 16.7) in vitro. The corresponding radioligand, I-123-(1) under bar, was synthe sized from a thienyl tributylstannane precursor using oxidative iodode stannylation methods. The radiochemical yield was 64-808 EOS (n = 5) a nd the purified product was >99% radiochemically purity with a specifi c activity >3,500 mCi/mu mol(>129,500 MBq/mu mol).