Facile preparation of Pt-II-nucleobase monoadducts with trans geometry: structural characterization and kinetics for Cl- hydrolysis reactions of trans-[PtCl(NH3)(2)(L-N7)](n+) (L=9-methyladenine or 9-methylhypoxanthine)

The employment of trans-[PtCl(OH)(NH3)(2)]. H2O as the platinum source offe rs a convenient and efficient way to prepare 1:1 adducts with the model nuc leobases 9-methyladenine (9-MeAde) and 9-methylhypoxanthine (9-MeHypH). The resulting complexes, trans-[PtCl(NH3)(2)(9-MeAde-N7)]ClO4 and trans-[PtCl( NH3)(2)(9-MeHyp-N7)]. 2H(2)O, were structurally characterized by X-ray crys tallography. The crystal packing of both complexes is stabilized by a hydro gen-bonding network involving primarily NH, ligands and perchlorate oxygens in trans-[PtCl(NH3)(2)-(9-MeAde-N7)]ClO4, and NH3 ligands and the C(6)O gr oup of the nucleobase in trans-[PtCl(NH3)(2)(9-MeHyp-N7)]. 2H(2)O. Three hy drogen bonds to the oxo group in the latter compound suggest that the negat ive charge caused by N1H deprotonation of the nucleobase is partly located on the oxygen atom; this is supported by the slightly larger down-field shi ft of C(6) over C(2) in the C-13 spectrum. However, the anticipated lengthe ning of the C(6)-O(6) bond upon N1H deprotonation was not verified by X-ray results. Kinetics for the Cl- hydrolysis in basic aqueous solution were fo llowed by Pt-195 NMR and HPLC analysis, which showed the formation of only one product in both cases with a Pt-195 chemical shift typical for a PtN3O coordination sphere. The comparable kinetic data found by these two methods reveal that the watts molecule acts as the nucleophile in the hydrolysis r eactions and that it displaces the Cl- ligand more readily in the 9-methyla denine complex.