Synthesis and radio-synthesis of prospective 2-nitroimidazole hypoxia PET tracers via thiazolidine ligation with 5-fluorodeoxyribose (FDR)

The first prospective fluorinated PET tracers for imaging hypoxia obtained via thiazolidine-ligation are reported. Three 1,2-thiol-amine linkers were combined with four different 2-nitroimidazole spacers via amide or urea bond formation. The resulting compounds were submitted to thiazolidine-ring-forming ligation reaction with the fluorinated carbohydrate L-5-fluoro-5-deoxy-ribose (FDR), affording the desired candidate PET tracers in variable yields. The same ligation reactions performed on L-ribose – a by-product of [18F]FDR radiosynthesis – under conditions mimicking a radiochemical production showed that the fluorinated adducts can be efficiently purified and isolated by HPLC. Finally, one of the prospective hypoxia tracers was successfully produced in radiolabelled form in 29.2% radiochemical yield from [18F]FDR.