Synthesis of 18F-labelled 2-(4′-fluorophenyl)-1,3-benzothiazole and evaluation as amyloid imaging agent in comparison with [ 11C]PIB

2-(4′-[ 18F]Fluorophenyl)-1,3-benzothiazole was synthesized as derivative of [ 11C]PIB to overcome the limitations associated with the short half-life of the carbon-11 label and was biologically evaluated in comparison with PIB. 2-(4′-[ 18F]fluorophenyl)-1,3-benzothiazole was synthesized as a fluorine-18 labelled derivative of the Pittsburg Compound-B (PIB), which has known affinity for amyloid β and promising characteristics as tracer for in vivo visualisation of amyloid deposits in patients suffering from Alzheimer’s disease (AD). Both the nitro-precursor 2-(4′-nitrophenyl)-1,3-benzothiazole and the non-radioactive reference compound were synthesized using a 1-step synthesis pathway. Labelling was achieved by direct aromatic nucleophilic substitution of the nitro-precursor using [ 18F]fluoride by heating for 20 min at 150 °C and with a radiochemical yield of 38%. The reference compound showed high affinity for amyloid in an in vitro competition binding study using human AD brain homogenates ( K i = 9.0 nM) and fluorescence imaging of incubated transgenic APP mouse brain slices confirmed binding to amyloid plaques. A biodistribution study in normal mice showed a high brain uptake at 2 min pi (3.20% ID/g) followed by a fast washout (60 min pi: 0.21% ID/g). A dynamic μPET study was performed in a transgenic APP and normal WT mouse, but, similar to [ 11C]PIB, no difference was seen in tracer retention between both kind of mice. The new 18F-labelled 2-phenylbenzothiazole showed excellent preclinical characteristics comparable with those of the 11C-labelled PIB.