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Efficient tritiation of the translocator protein (18kDa) selective ligand DPA-714

Damont, Annelaure; Garcia-Argote, Sébastien; Buisson, David-Alexandre; Rousseau, Bernard; Dollé, Frédéric

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  <dc:creator>Damont, Annelaure</dc:creator>
  <dc:creator>Garcia-Argote, Sébastien</dc:creator>
  <dc:creator>Buisson, David-Alexandre</dc:creator>
  <dc:creator>Rousseau, Bernard</dc:creator>
  <dc:creator>Dollé, Frédéric</dc:creator>
  <dc:description>DPA-714 (N,N-diethyl-2-(2-(4-(2-fluoroethoxy)phenyl)-5,7-dimethylpyrazolo[1,5-a]pyrimidin-3-yl)acetamide) is a recently discovered fluorinated ligand of the translocator protein 18 kDa (TSPO). Labelled with the short-lived positron emitter fluorine-18, this structure is today the radioligand of reference for in vivo imaging of microglia activation and neuroinflammatory processes with positron emission tomography. In the present work, an isotopically tritium-labelled version was developed ([3H]DPA-714), in order to access high resolution in vitro and ex vivo microscopic autoradiography studies, repeated and long-lasting receptor binding studies and in vivo pharmacokinetic determination at late time points. Briefly, DPA-714 as reference, and its 3,5-dibrominated derivative as precursor for labelling, were both prepared from DPA-713 in nonoptimized 32% (two steps) and 10% (three steps) yields, respectively. Reductive debromination using deuterium gas and Pd/C as catalyst in methanol, performed at the micromolar scale, confirmed the regioselective introduction of two deuterium atoms at the meta positions of the phenyl ring. Tritiodebromination was analogously performed using no-carrier tritium gas. HPLC purification provided &gt;96% radiochemically pure [3H]DPA-714 (7 GBq) with a 2.1 TBq/mmol specific radioactivity. Interestingly, additional hydrogen-for-tritium exchanges were also observed at the 5-methyl and 7-methyl positions of the pyrazolo[1,5-a]pyrimidine, opening novel perspectives in the labelling of compounds featuring this heterocyclic core.</dc:description>
  <dc:source>J Labelled Comp Radiopharm. 58(1) 1-6 (2015)</dc:source>
  <dc:subject>isotopic labelling</dc:subject>
  <dc:subject>TSPO 18 kDa</dc:subject>
  <dc:subject>hydrogen-for-tritium exchange</dc:subject>
  <dc:title>Efficient tritiation of the translocator protein (18kDa) selective ligand DPA-714</dc:title>
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