The three dimensional molecular structure of the adduct formed between the anticancer drug cisplatin and a DNA dinucleotide d(pGpG) has been determined by x-ray diffraction analysis at 1.37 Å resolution and refined to a final R-factor of 0.11. This structure, solved by using data from a previously reported crystal form in the space group C2221, resembles that found in the space group P2, 2, 2 (Sherman, et al” Science, 230, 412-417, 1985; ibid, J. Amer. Chem. Soc. 110, 7368-7381, 1988). In both structures, four crystallographically independent cis- [Pt(NH3)2 (d(pGpG))] molecules aggregate into a tetrameric cluster that is stabilized by a large number of intermolecular hydrogen bonds and base-base stacking interactions. In each molecule, the platinum atom is coordinated to the N7 atoms of two guanine bases arranged in a head-to-head orientation, resulting in a large dihedral angle between the guanines. Intermolecular guanine-guanine base pairings between different intrastrand crosslinked molecules are used extensively in the crystal lattice.
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