[ 11 C]TCH346, a compound acting on the glycolytic enzyme, glycerol-aldehyde-3-phosphate dehydrogenase, was produced under optimised conditions by methylation of the desmethyl compound with no-carrier added (n.c.a.) [ 11 C]methyl triflate. An i.v. injectable solution of n.c.a. [ 11 C]TCH346 containing 4040±1550MBq (n=6) containing a molar activity between 40 and 5700GBq/μmol and a radiochemical purity of >99% was obtained within 30min (after EOB) by irradiation of nitrogen gas containing 0.5% oxygen with 16.5MeV protons at 45μA for 30min. The alkylation reagent [ 11 C]methyl triflate was prepared via on-line conversion of [ 11 C]methyl iodide. For the formation of [ 11 C]methyl iodide, [ 11 C]carbon dioxide from the target chamber was reduced by a lithium aluminium hydride solution, and the methanol obtained on-line was converted using triphenylphosphine diiodide. The molar activity of [ 11 C]TCH346 could be improved from 40 up to nearly 5700GBq/μmol during the optimisation of the synthesis using the same stock solution of lithium aluminium hydride solution in tetrahydrofuran.