Improved syntheses of the PET radioligands, [11C]FLB 457, [11C]MDL 100907 and [11C]β-CIT-FE, by the use of [11C]methyl triflate

The highly reactive labelling agent, [11C]methyl triflate, was used to synthesise three recently developed PET radioligands. The labelling reactions were 11C-methylations of phenols for the preparations of the D2 receptor radioligand, [11C]FLB 457, and the 5-HT2A receptor radioligand, [11C]MDL 100907, and 11C-methylation of a carboxylic acid for the preparation of the dopamine transporter radioligand, [11C]β-CIT-FE. The synthesis of the 5-HT1A receptor radioligand, [O-methyl-11C]WAY-100635, was used to establish general reaction conditions for the methylation of phenols with [11C]methyl triflate. Compared to the previous use of [11C]methyl iodide in these radiosyntheses, [11C]methyl triflate demanded less precursor, allowed faster reactions and improved radiochemical yields. Normal-phase HPLC was used to speed up product purifications (except for [11C]β-CIT-FE). Hence, preparation times were shorter, resulting in radioligands with higher specific radioactivity. © 1998 John Wiley & Sons, Ltd.