METHYLATION OF AMIDE AND THIOL FUNCTIONS WITH [C-11] METHYL TRIFLATE,AS EXEMPLIFIED BY [C-11] NMSP, [C-11] FLUMAZENIL AND [C-11] METHIONINE

[C-11]Methyl triflate was compared with [C-11]methyl iodide as a label led precursor in the synthesis of PET radioligands through C-11-methyl ation of amide and thiol functions. [C-11]NMSP, [C-11]flumazenil and [ C-11]methionine were prepared in 50-75% radiochemical yields using sma ller amounts of precursors, shorter reaction times and lower reaction temperatures than previously used when these compounds were prepared f rom [C-11]methyl iodide. By minimizing the amount of base used in the synthesis of [C-11]methionine from [C-11]methyl triflate and L-homocys teine thiolactone in water a lower amount (1-2%) of D-[C-11]methionine was obtained. The results demonstrate that [C-11]methyl triflate is c ompatible with low concentrations of aqueous sodium hydroxide, which e nable its use in the preparation of PET radioligands through C-11-meth ylation of amide and thiol functions.