High molar activity of [11C]TCH346 via [11C]methyl triflate using the “wet” [11C]CO2 reduction method

[11C]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.) [11C]methyl triflate. An i.v. injectable solution of n.c.a. [11C]TCH346 containing 4040±1550 MBq (n=6) containing a molar activity between 40 and 5700 GBq/μmol and a radiochemical purity of >99% was obtained within 30 min (after EOB) by irradiation of nitrogen gas containing 0.5% oxygen with 16.5 MeV protons at 45 μA for 30 min. The alkylation reagent [11C]methyl triflate was prepared via on-line conversion of [11C]methyl iodide. For the formation of [11C]methyl iodide, [11C]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 [11C]TCH346 could be improved from 40 up to nearly 5700 GBq/μmol during the optimisation of the synthesis using the same stock solution of lithium aluminium hydride solution in tetrahydrofuran.