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The syntheses of [PtCl(2)(amp)] (amp = 2-pyridylmethylamine) and enantiomerically pure [PtCl(2)(R-pea)] and [PtCl(2)(S-pea)] (pea = 1-(2-pyridyl)ethylamine) and the crystal structure of [PtCl(2)(R-pea)] are reported. The reactions of [PtCl(2)(amp)] and of the enantiomers of [PtCl(2)(pea)] with d(GpG) and with a 52-base-pair oligonucleotide were investigated. Each of the reactions with d(GpG) resulted in the formation of three platinated bifunctional d(GpG) species in a ratio of 1:2:1. These species were shown to be a pair of isomers, one of which exists as a pair of slowly interconverting rotamers that can be separated by HPLC but reequilibrate after 5 days at 37 degrees C. The pyridyl moieties of the pyridylalkylamine ligands are constrained to lie in the coordination plane, and as a consequence, the rotation about the Pt-N7 bond of the adjacent guanine is highly restricted. 2D NMR investigations were carried out on the isomer of [Ptd(GpG)(amp)] that did not form separable rotamers and identified it as the isomer having the pyridine adjacent to the 5'-guanine of the d(GpG). The reaction of each of the three [PtCl(2)(py-R)] complexes (py-R = amp or pea) with a 52-base-pair oligonucleotide resulted in the formation of the same three bifunctional d(GpG) adducts in approximately the same ratios as the reactions with d(GpG), indicating that negligible stereoselectivity results from interactions between the complexes and duplex DNA.

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The crystal structure of [PtCl 2 (cis-1,3-chxn)] (cis-1,3-chxn = (cis-cyclohexane-1,3-diamine)) as the dimethyformamide solvate is reported. When [PtCl 2 (cis-1,3-chxn)] binds to d(GpG), two isomers are formed that are readily separated by HPLC. Both the HPLC and GFAAS studies of the products show that the isomers form in a 1 : 1 ratio. Competition experiments involving d(GpG) and the aquated and nonaquated forms of [PtCl 2 (cis-1,3-chxn)] and [PtCl 2 (NH 3 ) 2 ] showed that the slower binding of the former complex was due to slower aquation and not steric bulk. 1D and 2D NMR studies of the [Ptd(GpG)(cis-1,3-chxn)] isomers showed that both the dinucleotide and the diamine were highly fluxional, even at low temperatures, and this prevented formation of strong cross peaks in the NOESY and ROESY spectra and hence identification of the isomers. [PtCl 2 (cis-1,3-chxn)] was reacted with a 52-mer oligonucleotide having six GpG binding sites and the products were enzymatically digested and separated by HPLC. The two [Ptd(GpG)(cis-1,3-chxn)] stereoisomers were the only significant platinated products, again forming in a 1 : 1 ratio although it had been anticipated that stereoselectivity would be observed in the reaction with the 52-mer because of the potential for steric interactions with the cis-1,3-chxn ligand. Molecular modelling revealed that the observed lack of stereoselectivity was due to the ability of the cis-1,3-chxn ligand to adopt a continuum of conformations that allow it to avoid severe steric clashes with the DNA. † Electronic supplementary information (ESI) available: figures showing HPLC chromatograms and NMR spectra. See