L-[Methyl-(11C)]-methionine of high enantiomeric purity production via online-11C-methylation of L-homocysteine thiolactone hydrochloride

Abstract

L-[methyl-(11C)]-methionine ([11C]MET), labelled with carbon-11 (T1/2 = 20 min), is the most commonly used amino acid radiotracer for PET diagnostics of brain tumors. The production of [11C]MET via on-line 11C-methylation of L-homocysteine thiolactone hydrochloride (lactone) on C18 solid-phase extraction cartridge creates a problem of insufficient enantiomeric purity (content of L-isomer) of the product. The results of a systematic study of the influence of reaction parameters (lactone/base and the EtOH/H20 ratios, time of 11C-methylation) on the content of L-isomer in the preparation are presented. The developed method of on-line [11C]MET synthesis allows to obtain a product with a sufficiently high radiochemical yield (75 +/- 3%, n = 100, based on [11C]CH3I) and reliably high content of L-isomer (93.7 +/- 0.5%) satisfying the requirements of clinical applications. [11C] MET synthesis was performed on a fully automated module designed by the Institute of Human Brain (IHB RAS).