Chelator-accelerated one-pot 'click' labeling of small molecule tracers with 2-[¹⁸F]fluoroethyl azide

Molecules. 2013 May 10;18(5):5335-47. doi: 10.3390/molecules18055335.

Abstract

2-[¹⁸F]Fluoroethyl azide ([¹⁸F]FEA) can readily be obtained by nucleophilic substitution of 2-azidoethyl-4-toluenesulfonate with [¹⁸F]fluoride (half-life 110 min), and has become widely used as a reagent for 'click' labeling of PET tracers. However, distillation of [18F]FEA is typically required, which is time-consuming and unpractical for routine applications. In addition, copper(I)-catalyzed cycloaddition of [¹⁸F]FEA with non-activated alkynes, and with substrates containing labile functional groups, can be challenging. Herein, we report a highly efficient and practical ligand-accelerated one-pot/two-step method for 'click' labeling of small molecule tracers with [¹⁸F]FEA. The method exploits the ability of the copper(I) ligand bathophenanthrolinedisulfonate to accelerate the rate of the cycloaddition reaction. As a result, alkynes can be added directly to the crude reaction mixture containing [¹⁸F]FEA, and as cyclisation occurs almost immediately at room temperature, the reaction is tolerant to labile functional groups. The method was demonstrated by reacting [¹⁸F]FEA with a series of alkyne-functionalized 6-halopurines to give the corresponding triazoles in 55-76% analytical radiochemical yield.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Azides / chemistry*
  • Catalysis
  • Click Chemistry / methods*
  • Copper / chemistry*
  • Fluorine Radioisotopes / chemistry*
  • Hydrocarbons, Fluorinated / chemistry*
  • Isotope Labeling / methods*
  • Positron-Emission Tomography / methods

Substances

  • Azides
  • Fluorine Radioisotopes
  • Hydrocarbons, Fluorinated
  • Copper