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 monofunctional cisplatin model compounds, [PtCl(NH3 )(3)] Cl and [PtCl(dien)] Cl, to Guanosine-5'-triphosphate (5'GTP) is described. For comparison also the binding of [PtCl(Nn(3))(3)]Cl to d( TpG) has been studied. It is shown that in all cases the platinum tria m(m)ine binds to guanine-N7. The conformations of the sugar rings have been determined using high-resolution NMR techniques. The relative am ount of the N conformer of the sugar ring of 5'GTP increases upon plat ination. Only minor differences were observed between the 5'GTP adduct s of [PtCl(NH3)(3)] Cl and [PtCl(dien)] Cl. The conformational equilib rium of the sugar rings of d(TpG), however, barely shows any change up on platination. For both cases the conformation is assumed to result f rom the interaction between the negatively charged (tri)phosphate grou p and the positively charged platinum group. This interaction causes a strain in the 5'GTP adducts resulting in the observed change in the c onformational equilibrium of the sugar ring. In the case of d(TpG) suc h a strain is not found, which is ascribed to the lower charge on the phosphate group.