title: The preparation of a carbon-11 labelled neurohormone--[11C]melatonin.
abstract: Melatonin, a hormone of the pineal gland, has been labelled with the positron-emitting radionuclide, carbon-11 (t1/2 = 20.4 min), for study in vivo by positron emission tomography. Thus a novel labelling agent, [11C]acetyl chloride, was prepared by the carbonation of methylmagnesium bromide with cyclotron-produced [11C]carbon dioxide followed by treatment with phthaloyl dichloride. Acylation of 5-methoxytryptamine then affords [11C]melatonin, which is purified by HPLC and formulated for intravenous injection. The preparation requires 35 min from the end of radionuclide production. It provides [11C]melatonin in 13% radiochemical yield (decay-corrected from 11CO2) and in high specific activity. Radiochemical and chemical purity were demonstrated by HPLC and TLC. The validity of the radiosynthesis was also confirmed by a parallel synthesis of [13C]melatonin and examination of the product by 13C-NMR spectroscopy and mass spectrometry.
authors.affiliation: MRC Cyclotron Unit, Hammersmith Hospital, London, U.K.
authors.forename: D
authors.initials: D
authors.lastname: Le Bars
authors.forename: S K
authors.initials: SK
authors.lastname: Luthra
authors.forename: V W
authors.initials: VW
authors.lastname: Pike
authors.forename: C L
authors.initials: CL
authors.lastname: Duc
mesh_terms: D002245:Carbon Dioxide; D002247:Carbon Isotopes; D002851:Chromatography, High Pressure Liquid; D007553:Isotope Labeling / Q000379:methods; D008550:Melatonin / Q000302:isolation & purification
chemical_list: D002247:Carbon Isotopes; D002245:Carbon Dioxide; D008550:Melatonin