Synthesis of the labeled D1 receptor antagonist SCH 23390 using [11C] carbon dioxide

A new synthesis is described for the production of the positron emitting radiopharmaceutical R-(+)-7-chloro-8-hydroxy-2,3,4,5-tetrahydro-3-N-[11C]methyl-1-phenyl-1H- 3-benzazepine (SCH 23390, 2a). This novel method involves reductive carboxylation, in which [11C]CO2 is reacted with the trimethylsilyl derivative of the desmethyl compound (SCH 24518, 1a) followed by treatment with lithium aluminum hydride, to afford no carrier added 11C-labeled SCH 23390. The procedure gave chemically and radiochemically pure 11C-labeled SCH 23390 in 53-72% radiochemical yield with an unoptimized specific activity of 40 Ci/mmol within 45-50 min from the end of bombardment.