FAST ROUTINE PRODUCTION OF L-[C-11-METHYL]METHIONINE WITH AL2O3/KF

No-carrier-added (nea) L-[C-11-methyl]methionine was prepared via the very fast S-alkylation of L-homocysteine adsorbed on Al2O3/KF with [C-11]iodomethane at room temperature in ethanol. The alkylation was realized with a radiochemical yield of 94 +/- 4% EOB (n = 20). More than 90% (n = 20) of the precursor L-homocysteine remained adsorbed on the solid support and was eliminated by a simple filtration. After reaction, neither racemization nor by-product were detected. The purification process was thus limited to a C18 Sep-Pak followed by an alumina Sep-Pak. The radiochemical purity measured on the final solution was shown to be > 99%. The only chemical contaminant was L-homocysteine (+/- 10 mu g). With this new technique, L-[C-11-methyl]methionine was ready for injection within 10 min from [C-11]CO2 with a specific activity ranging around 37 +/- 5.6 GBq (1 +/- 0.15 Ci)/mu mol EOB. Through this procedure L-[C-11-methyl]methionine can be prepared without preparative RPLC purification. This is an important simplification for the fast routine production of one of the most widely used radiopharmaceutical compounds for PET.