Platinum(II) complexes catalyze reactions between platinum(IV) complexes and 9-methylxanthine‡

Abstract

Reactions between 9-methylxanthine (9-mxan) and platinum(IV) complexes having ammine, organic amine and chloro ligands are speeded up dramatically by additions of small amounts of the analogous platinum(II) complex. Complexes studied include cis-dichlorodiammineplatinum(II) {cis-[Pt(NH₃)₂Cl₂] 1a}, cis-tetrachlorodiammineplatinum(IV) {cis-[Pt(NH₃)₂Cl₄] 1b}, cis-dichloroammine(cyclohexylamine)platinum(II) {cis-[Pt(NH₃)(cha)Cl₂] 2a}, cis-tetrachloroammine(cyclohexylamine)platinum(IV) {cis-[Pt(NH₃)(cha)Cl₄] 2b}, chloro(diethylenetriamine)platinum(II) chloride {[Pt(dien)Cl]Cl 3a} and mer-trichloro(diethylenetriamine)platinum(IV) chloride {mer-[Pt(dien)Cl₃]Cl 3b}. For a 10∶90 molar ratio of 1a∶1b, the half-life for platinum(IV)–9-mxan product formation is approximately 3 h whereas t_½ for pure 1b–9-mxan product formation is greater than 90 h, indicating a 30 times rate enhancement upon addition of 10% of the platinum(II) complex. For the 2a∶2b pair, an eight-fold rate enhancement is observed over that for pure 2b–9-mxan. This behavior may be related to the chloride bridging mechanism first elucidated for platinum-(II) and -(IV) complexes. Since known platinum-(II) and -(IV) antitumor drugs target nucleobases of DNA to effect cell death in malignant cells, the reactions discussed may shed light on platinum antitumor compound reaction mechanisms.