New method for routine production of L‐[methyl‐11C]methionine: in loop synthesis

A fast, clean and reproducible method for the manufacture of the radiotracer L‐[methyl‐11C]methionine is reported. The reaction at room temperature of the non‐radioactive precursor L‐homocysteine (1 mg solution in ethanol/water 50/50) with [11C]CH3I in an HPLC loop led to the formation of the desired radiotracer with a high radiochemical yield (38.4±4.1% end of synthesis) in a short production time (12 min). Radiochemical purity of the final radiotracer was 99.9±0.05%. Specific activities in the range 11–45 GBq/µmol were obtained. The presence of the undesired enantiomer (D‐[methyl‐11C]methionine) was not detected in any of the cases.