COMBINED NMR AND MOLECULAR MECHANICS STUDY OF THE ISOMERS FORMED IN THE REACTION OF DICHLORO(1,4-DIAZACYCLOHEPTANE)PLATINUM(II) WITH THE DINUCLEOTIDE D(GPG)

The reaction of [Pt(hpip)Cl-2] (hpip = homopiperazine = 1,4-diazacyclo heptane) with d(GpG) yields two apparently isomeric products, separabl e by HPLC. These have been characterized by a combination of 2D NMR an d molecular mechanics modeling. NOESY correlations between the H8 prot ons show that both products are head-to-head isomers, and NOESY correl ations between the d(GpG) dinucleotide and the diamine ligand show tha t the difference between the isomers lies in the orientation of the tw o and three carbon chains of the hpip ligand with respect to the heads (H8 protons) of the guanine bases. Molecular mechanics calculations y ield total energies that are consistent with the observation of the tw o isomers in approximately equal amounts.