Kinetic study of the reaction between an antitumor 15N labeled trans-platinum iminoether complex and GMP by [1H, 15N] HMQC NMR

Abstract

The kinetics and mechanism of binding of the ¹⁵N-labeled anticancer compound trans-[PtCl₂{E-HNC(OMe)Me}₂] (trans-EE) to guanosine 5′-monophosphate (5′-GMP) and the tripeptide glutathione (GSH) have been investigated by 2D [¹H, ¹⁵N] HMQC NMR spectroscopy. The different reaction products can easily be identified as crosspeaks in the 2D NMR spectra. The integrated peak intensities vs. time are used to obtain rate constants by a non-linear optimization procedure. The calculated rate constants (forward and back reaction) for hydrolysis of the first (k₁ and k₋₁) and second chloride (k₂ and k₋₂) are: k₁ = 2.1 × 10⁻⁴ s⁻¹, k₋₁ = 890 × 10⁻⁴ M⁻¹ s⁻¹; k₂ = 0.025 × 10⁻⁴ s⁻¹, and k₋₂ = 4.6 × 10⁻⁴ M⁻¹ s⁻¹ at 298 K. The corresponding literature values for the inactive trans-[PtCl₂(NH₃)₂] compound exhibit a large dispersion. The formation of the mono-chloro GMP adduct takes place via a bimolecular process involving the mono-chloro mono-aqua species and the entering nucleotide (k₃ = 2700 × 10⁻⁴ M⁻¹ s⁻¹), the concentration of this adduct reaches a maximum value after about 6 hours at 298 K. Subsequently, mono-aqua GMP (k₄ = 0.131 × 10⁻⁴ s⁻¹, k₋₄ = 10.0 × 10⁻⁴ M⁻¹ s⁻¹) and bifunctional GMP adducts (k₅ = 99.6 × 10⁻⁴ M⁻¹ s⁻¹) are formed in successive steps. Competition reactions of trans-EE with GSH and GMP show a clear preference for GSH adduct formation. Some of the reactions were run both with and without phosphate buffer to assess the degree of platinum–phosphate binding.