[en] No-carrier-added (nca) L-[11C-methyl]methionine was prepared via the very fast S-alkylation of L-homocysteine adsorbed on AI203/KF with [11C]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 µg). With this new technique, L-[11C-methyl]methionine was ready for injection within 10 min from [11C]CO2 with a specific activity ranging around 37 + 5.6 GBq (1 +/- 0.15 Ci)//tmol EOB. Through this procedure L-[11C-methyl]methionine can be prepared without preparative HPLC purification, This is an important simplification for the fast routine production of one of the most widely used radiopharmaceutical compounds for PET.
Centre de Recherches du Cyclotron - CRC
Fonds de la Recherche Scientifique (Communauté française de Belgique) - F.R.S.-FNRS