Reversible Covalent and Supramolecular Functionalization of Water-Soluble Gold(I) Complexes.

The ligation of gold(I) metalloamphiphiles with biomolecules is reported, using water-soluble Au-I-N-alkynyl substituted maleimide complexes. For this purpose, two different polar ligands were applied: 1) a neutral, dendritic tetraethylene glycol-functionalized phosphane and 2) a charged, sulfonated N-heterocyclic carbene (NHC). The retro Diels-Alder reaction of a furan-protected maleimide gold(I) complex, followed by cycloaddition with a diene-functionalized biotin under mild conditions leads to a novel gold(I) metalloamphiphile. The strong streptavidin-biotin binding affinity in buffered aqueous solution of the resulting biotin alkynyl gold(I) phosphane conjugate remains intact. The cytotoxicity of the biotinylated gold(I) complex against a T47D human breast cancer cell line is higher than for cisplatin.