EFFECTS OF ASYMMETRY AND BULKY SUBSTITUENTS IN AMINE LIGANDS OF CIS-DI(AMINE)DICHLOROPLATINUM COMPLEXES ON THE STRUCTURE OF ADDUCTS FORMED WITH ADJACENT GUANINES IN NUCLEIC-ACIDS

Platinum adducts obtained from the reaction of 3'-O,5'-O-phosphodiguanosine, r(GpG), with the asymmetric complexes cis-[PtCl2L(L')] (L = NH3; L' = alkylamine such as NH2Me, NHMe2 and NHEt2; LL' = N,N-dimethylethylenediamine) have been structurally characterized by H-1 NMR techniques. Two different adducts, in which platinum co-ordinates to the N7 sites of both guanines, were obtained as geometrical isomers, one with the NH3 group cis to the 5' base and the other with the alkylamine cis to it. Apparently, the structures of these platinum adducts, cis-[PtL(L')(GpG-N7,N7)]+, are similar to that of the known cis-[Pt(NH3)2(GpG-N7,N7)]+, i.e. with an anti-anti configuration and with the N conformer of the sugar as the 5' residue. However, the asymmetric character of the non-leaving group induces a slight but significant deviation in the relative orientation of the two guanines which increases with increasing bulkiness of the alkylamine group.