title: The chemistry of dinuclear analogues of the anticancer drug cisplatin. A DFT/CDM study.
abstract: The mechanism of the formation of dinuclear platinum(II) mu-hydroxo complexes from cisplatin hydrolysis products, their interconversion, decomposition, and reactions with biomolecules has been explored using a combined DFT/CDM approach. All activation barriers for the formation of [cis-{Pt(NH(3))(2)(X)}-(mu-OH)-cis-{Pt(NH(3))(2)(Y)}](n)()(+) (X, Y = Cl, OH(2), OH) via nucleophilic attack of a hydroxo complex on an aqua complex are lower than the activation barriers for cisplatin hydrolysis. Considering therapeutic Pt(II) concentrations in tumors, however, only the reaction between two molecules of cis-[Pt(NH(3))(2)(OH(2))(OH)](+) (E) yielding [cis-{Pt(NH(3))(2)(OH(2))}-(mu-OH)-cis-{Pt(NH(3))(2)(OH)}](2+) (5) remains kinetically superior to cisplatin hydrolysis. 5 is strongly stabilized by intramolecular hydrogen bonding between the terminal aqua and hydroxo ligands, resulting in an unusually high pK(a) of 5 and a low pK(a) of its conjugate acid. Unimolecular cyclization of 5 yields the dimers [cis-{Pt(NH(3))(2)}(mu-OH)](2)(2+) (7a with antiperiplanar OH groups and 7b with synperiplanar OH groups). The electronic structure of several diplatinum(II) complexes has been analyzed to clarify whether there are metal-metal interactions. The overall reactivity to guanine (Gua) and dimethyl sulfide (Met, representing the thioether functional group of methionine) increases in the order 5 < 7a approximately 7b < mononuclear complexes, whereas the kinetic selectivity to Gua relative to Met increases in the order 7a approximately 5 < 7b approximately monocationic mononuclear complexes < dicationic mononuclear complex. The results of this work (i) help assess whether dinuclear metabolites play a role in cisplatin chemotherapy, (ii) elucidate the toxicity and pharmacological inactivity of [cis-{Pt(NH(3))(2)}(mu-OH)](2)(2+), and (iii) suggest future investigations of dinuclear anticancer complexes that contain one mu-hydroxo ligand.
authors.affiliation: ETH Zurich, USI Campus, Computational Science, D-CHAB, 6900 Lugano, Switzerland. metal-in-medicine@phys.chem.ethz.ch
authors.forename: Dirk V
authors.initials: DV
authors.lastname: Deubel
mesh_terms: D000970:Antineoplastic Agents / Q000737:chemistry; D002945:Cisplatin / Q000031:analogs & derivatives* / Q000737:chemistry*; D006147:Guanine / Q000737:chemistry; D006860:Hydrogen Bonding; D006868:Hydrolysis; D008958:Models, Molecular; D010984:Platinum / Q000737:chemistry; D013440:Sulfides / Q000737:chemistry; D013816:Thermodynamics
chemical_list: D000970:Antineoplastic Agents; D013440:Sulfides; D010984:Platinum; D006147:Guanine; D002945:Cisplatin; C004784:dimethyl sulfide