Exchange reactions between albumin-Au(I)-PEt₃ complex and Me₃PAuCl or iPr₃PAuCl: ³¹P NMR spectroscopic studies

The AlbSAuPEt₃ complex was prepared in vitro by reacting AlbSH with auranofin.§ It is shown that the Et₃PAu⁺ entity is liable to exchange in the presence of Me₃PAuX and iPr ₃PAuX (X = Cl^- or AtgS^-; AtgS^- = tetraacetyl thioglucose). ³¹P NMR spectroscopy was used to follow these exchange reactions. Either Me₃PAu⁺ or iPr ₃PAu⁺ replaces Et₃PAu⁺ from the AlbSAuPEt₃ complex. Since the iPr₃P ligand is bulkier (reflected by its bigger Tollman cone angle), it is surprising that it replaces Et₃PAu⁺ almost equally as well as Me₃PAu ⁺. It is also demonstrated that Et₃PAu⁺ bound to the weak binding sites of albumin (primarily histidines) can be transferred to the stronger binding site which is AlbSAuPEt₃ to form the bis complex AlbS(AuPEt₃)₂. The transfer of Et ₃PAu⁺ between protein species is relevant to mechanism by which gold may be transferred between proteins in vivo.