Radiosynthesis of NCA [carbonyl-11C]6-fluoromelatonin

A method is described for the preparation of [carbonyl-11C]6-fluoromelatonin for intravenous injection and potential study of the melatonin system in vivo by positron emission tomography. The preparation is based on the acetylation of 6-fluoro-5-methoxytryptamine with NCA [1-11C]acetyl chloride (itself prepared from cyclotron-produced [11C]carbon dioxide) and purification by HPLC. It gives chemically and radiochemically pure [carbonyl-11C]6-fluoromelatonin in 35% radiochemical yield (from [11C]CO2, decay-corrected) within 35 min from the end of radionuclide production and with high specific activity e.g. 1.6 GBq/mumol (43 mCi/mumol) at the end of synthesis from 1.1 GBq (30 mCi) of [11C]carbon dioxide.