Synthesis and biological evaluation of [18F]fluorovinpocetine,a potential PET radioligand for TSPO imaging

Despite of various PET radioligands targeting the translocator protein TSPO 18-KDa are used for the investigations of neuroinflammatory conditions associated with neurological disorders, development of new TSPO radiotracers is still an active area of the researches with a major focus on the ¹⁸F-labelled radiotracers. Here, we report the radiochemical synthesis of ¹⁸F]vinpocetine, fluorinated analogue of previously reported TSPO radioligand, ¹¹C]vinpocetine. Radiolabeling was achieved by ¹⁸F]fluoroethylation of apovincaminic acid with ¹⁸F]fluoroethyl bromide. ¹⁸F]vinpocetine was obtained in quantities >2.7 GBq in RCY of 13% (non–decay corrected), and molar activity >60 GBq/µmol within 95 min synthesis time. Preliminary PET studies in a cynomolgus monkey and metabolite studies by HPLC demonstrated similar results by ¹⁸F]vinpocetine as for ¹¹C]vinpocetine, including high blood-brain barrier permeability, regional uptake pattern and fast washout from the NHP brain. These results demonstrate that ¹⁸F]fluorovinpocetine warrants further evaluation as an easier accessible alternative to ¹¹C]vinpocetine.