Efficient radiosynthesis of carbon-11 labelled uncharged Thioflavin T derivatives using [ 11C]methyl triflate for β -amyloid imaging in Alzheimer's Disease with PET

The synthesis of carbon-11 amino function labelled uncharged Thioflavin T derivatives is known to be performed by reaction of the demethyl-precursors with [ 11C]methyl iodide but the labelling yields are only mediocre. The use of [ 11C]methyl triflate improved the radiochemical yield of three potential β -amyloid imaging PET-radiotracers significantly. Performance of the labelling reaction by reacting the corresponding precursor molecules with [ 11C]methyl triflate for 1 min at 80 °C led to radiochemical yields of 44±10% ( n = 5 ) for [ 11C]6-Me-BTA-1, 68±4% ( n = 10 ) for [ 11C]BTA-1 and 58±2% ( n = 5 ) for [ 11C]6-OH-BTA-1 with respect to [ 11C]methyl triflate. In production runs (60 min, 50 μA) up to 6500 MBq (mean: 4000±1900 MBq) of [ 11C]6-Me-BTA-1, 7900 MBq (mean: 6000±1000 MBq) of [ 11C]BTA-1 and 7100 MBq (mean: 6300±600 MBq) of [ 11C]6-OH-BTA-1 could be obtained ready for intravenous injection. The radiochemical purity was >95% with specific activities in the range of 80–120 GBq/μmol (EOS) within a total synthesis time of less than 40 min after EOB.