Target identification of a macrocyclic hexaoxazole G-quadruplex ligand using post-target-binding visualization

Chem Commun (Camb). 2020 Nov 4;56(85):12905-12908. doi: 10.1039/d0cc04957c. Epub 2020 Oct 8.


Macrocyclic hexaoxazoles (6OTDs) are G-quadruplex (G4) ligands, and some derivatives, such as L2H2-6OTD (1a) bearing two aminobutyl side chains, show cytotoxicity towards cancer cells. To identify the cellular target of 1a, we employed a post-target-binding strategy utilizing click reaction (Huisgen cyclization) between the azide-conjugated ligand L2H2-6OTD-Az (1b) and the cell-permeable dye CO-1 bearing a strained alkyne moiety and the BODIPY fluorophore under Cu-free conditions. We confirmed that introduction of the small azide group did not alter the physical or biological properties, including anti-cancer activity, of 1a, and we also demonstrated bias-free localization of CO-1. The post-binding visualization strategy suggested that L2H2-6OTD (1a) colocalized with RNA G4 in living cells.

MeSH terms

  • Binding Sites
  • Cell Line, Tumor
  • G-Quadruplexes
  • Humans
  • Ligands
  • Macrocyclic Compounds / chemistry*
  • Molecular Structure
  • Oxazoles / chemistry*


  • Ligands
  • Macrocyclic Compounds
  • Oxazoles