The disclosure relates to compounds of the general formula I, wherein D is deuterium, R1 is selected from methyl, ethyl, n-propyl, n-butyl, iso-butyl； R2 is fluorine, [18F]fluorine or a leaving group, wherein leaving groups are selected from halogen, C1-C6-alkylsulfonyloxy, which is optionally substituted by fluorine, and arylsulfonyloxy, which is optionally substituted by hydrogen, methyl, halo and nitro； n and m are selected from 0 and 1 with the proviso that if n = 0, m must be 1, and if n = 1, m must be 0, and if R2 is fluorine, n must be 1 and m must be 0. The disclosure also relates to the [18F] labelled compounds and compositions comprising these compounds for use in PET imaging of CNS diseases, including Alzheimer&rsquo；s disease. The disclosure also relates to a method to synthesise these compounds and kits containing them.
