Conformational changes in d (TpG) and 5′GTP induced by monofunctional binding of [PtCl(NH3)3]Cl and [PtCl(dien)] are small

The binding of the monofunctioal cisplatin model compounds PtCl(NH₃)Cl and PtCl(dien)]Cl, to Guanosine-5′-triphosphate (5′GTP) is described. For comparison also the binding of PtCl(NH₃)₃]Cl to d(TpG) has been studied. It is shown that in all cases the platinum triam(m)ine binds to guanine-N7. The conformations of the sugar rings have been determined using high-resolution NMR techniques. The relative amount of the N conformer of the sugar ring of 5′GTP increases upon platination. Only minor differences were observed between the 5′GTP adducts of PtCl(NH₃)₃]Cl and PtCl(dien)]Cl. The conformational equilibrium of the sugar rings of d(TpG), however, barely shows any change upon platination. For both cases the conformation is assumed to result from the interaction between the negatively charged (tri)phosphate group and the positively charged platinum group. This interaction causes a strain in the 5′GTP adducts resulting in the observed change in the conformational equilibrium of the sugar ring. In the case of d(TpG) such a strain is not found, which is ascribed to the lower charge on the phosphate group.