High efficiency preparation of L-[S-methyl-11C]methionine by on-column [11C]methylation on C18 Sep-Pak

A novel approach to the synthesis of L-[S-methyl-¹¹C]methionine, (¹¹C]MET) is described which involves a commercial C18 Sep-Pak Plus as a solid-phase support material for the [¹¹C]methylation step. The present method, which uses [¹¹C]CH₃I produced by the classical LiAlH₄/HI route, supplies [¹¹C]MET ready for injection within 11 min from the end of bombardment (EOB) with a radiochemical yield, decay corrected at EOB, of 78% and a radiochemical purity at the end of synthesis (EOS) higher than 99%. The required setup is extremely simple and easy to automate and can be reset for a further synthesis within few minutes. Moreover, due to its versatility, the method can be utilized for the production of other radiopharmaceuticals requiring a simple [¹¹C]methylation.