Crystal and molecular structures of asymmetric cis- and trans-platinum(II/IV) compounds and their reactions with DNA fragments

The asymmetrically substituted platinum(II) complexes cis-Pt(NH3)(c-C6H11NH2)Cl-2 and trans-Pt(NH3)(c-C6H11NH2)Cl-2 have been synthesized and their crystal structures have been determined. Crystals of cis-Pt(NH3)(c-C6H11NH2)Cl-2 (1) are orthorhombic, space group Pbca (no. 61) with a = 10.1994(12), b = 10.494(2), c = 18.826(2) Angstrom, Z = 8. The structure refinement converged to R1 = 0.0518 and wR2 = 0.1143. Crystals of trans-Pt(NH3)(c-C6H11NH2)Cl-2 (2) are monoclinic, space group P2(1)/c (no. 14) with a = 12.141(3), b = 6.0965(9), c = 19.864(3) Angstrom, beta = 118.71(2)degrees, Z = 4. The structure refinement converged to R1 = 0.0711 and wR2 = 0.1846. In addition, the Pt(IV) analogues with axial hydroxide ligands have been synthesized. Also the corresponding bis(carboxylato)platinum(IV) compound of formula trans,cis,cis-Pt(NH3)(c-C6H11NH2)Cl-2(OOCCH3)(2) has been obtained by conversion of the hydroxide with acetic anhydride. Reactions of these platinum complexes with 9-methylhypoxanthine and guanosine-5'-monophosphate (5'-GMP) have been studied in significant detail. The course of the reactions was followed by NMR spectroscopy, and H-1 and Pt-195 techniques were used to identify the formation of the products. It was found that the Pt(II) compounds easily react with the bases at the N7 position, whereas the Pt(IV) compounds react very slowly (for trans,cis,cis-Pt(NH3)(c-C6H11NH2)Cl-2(OOCCH3)(2)) or not at all (for trans, trans, trans-Pt(NH3)(c-C6H11NH2)Cl-2(OH)(2)), Only in the presence of glutathione does a reaction of the latter with 5'-GMP takes place. In this case a major product was found to be the reduced trans-Pt(II) complex with one molecule of 5'-GMP and one molecule of S-bonded glutathione.