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@INPROCEEDINGS{Humpert:1026496,
      author       = {Humpert, Swen and Menges, Tobias and Keuthen, Yannick and
                      Zlatopolskiy, Boris and Neumaier, Bernd},
      title        = {{E}valuation of tetramethylammonium salts in
                      minimalist-like {SNA}r radiofluorinations},
      reportid     = {FZJ-2024-03440},
      year         = {2023},
      abstract     = {Objective: Tetraalkylammonium salts like Et 4NX or Bu4NX
                      repre-sent valuable alternatives to conventional K2 CO3
                      /K2.2.2., enablingpreprocessing of [ 18 F]fluoride without
                      azeotropic drying. Additionally,the selection of appropriate
                      counter ions like bicarbonate or triflateallow the
                      adjustment of the basic strength in the reaction medium,
                      e,g.,for radiolabeling of sensitive substrates or
                      Cu-mediated 18 F-fluorin-ation. Recently, NMe4 HCO 3 was
                      reported to improve the yield in SNArradiofluorination
                      reactions if added to azeotropically dried [ 18F]KF·K2.2.2.
                      The enhanced reactivity was attributed to in situ
                      formationof strongly nucleophilic [ 18 F]Me4 NF [1]. Herein,
                      we describe theazeotropic drying-free preparation of [ 18
                      F]Me4NF and evaluation of itsreactivity in SNAr 18
                      F-fluorinations compared to widely applied [18 F]Et
                      4NF.Methods: Aqueous [ 18 F]fluoride was loaded onto a QMA
                      cartridgeand the resin was washed with anhydrous MeOH. [18
                      F]F– was elutedwith a solution of the respective salt (18
                      µmol) in MeOH. Evaporationof MeOH directly afforded
                      anhydrous [ 18 F]R4 NF/X (R = Me, Et; X = OTf,HCO3 ) salts.
                      The latter were comparatively evaluated using a series
                      of(hetero)aromatic substrates containing various leaving
                      groups (-F, -Cl,-Br, -I, Me3 N-+, -NO2 , -OTf, DABCO-onium,
                      sulfonium and iodonium).Suboptimal reaction conditions (7
                      µmol of precursor, DMF, 100 °C,10 min) were intentionally
                      used to obtain significant differences inradiochemical
                      conversions (RCCs) even for highly reactive
                      precursors.Results: Minimalist preprocessing of [
                      18F]fluoride furnished therespective anhydrous [ 18F]NR4 F/X
                      in radiochemical yields of $>95\%within$ only 5 min. With
                      two exceptions concerning isotopic exchangeon heteroarenes
                      (entries 5 and 6), the RCCs for labeling of the
                      modelsubstrates were consistently higher for [ 18F]Me4NF/X
                      in comparison tothe corresponding [ 18 F]Et4 NF/X salt. On
                      average the absolute differenceamounted to $19\%$ (or a 3.5
                      fold relative increase, respectively). The lessreactive
                      DABCO precursors 16 and 17 furnished exclusively the
                      SN2ring-opening products. With regard to the counter ion,
                      less basicconditions appeared to be preferable, since 9 vs.
                      2 precursors gavehigher RCCs with triflate vs. bicarbonate
                      counter ion. The counter ionhad no impact on
                      radiofluorination of precursors bearing trimethy-lammonium
                      and DABCO-ammonium leaving groups.Conclusions: [ 18
                      F]Me4NF/X can be rapidly prepared by minimalistpreprocessing
                      and is considerably more reactive than commonly used[ 18
                      F]TEAF. In particular, [ 18 F]Me4NF/OTf is a promising
                      radiofluorina-tion agent, which afforded high RCCs for a
                      broad scope of radiolabelingprecursors.ReferenceLee et al.,
                      J. Org. Chem. 2021, 86, 14121–14130.},
      month         = {May},
      date          = {2023-05-22},
      organization  = {25th International Symposium on
                       Radiopharmaceutical Sciences, Honolulu
                       (USA), 22 May 2023 - 26 May 2023},
      subtyp        = {After Call},
      cin          = {INM-5},
      cid          = {I:(DE-Juel1)INM-5-20090406},
      pnm          = {5253 - Neuroimaging (POF4-525)},
      pid          = {G:(DE-HGF)POF4-5253},
      typ          = {PUB:(DE-HGF)6},
      doi          = {10.34734/FZJ-2024-03440},
      url          = {https://juser.fz-juelich.de/record/1026496},
}