Pure and Applied Chemistry

Abstract: The products obtained by forcing the reaction with nucleosides (guanosine, Guo, and adenosine, Ado) of potential anticancer drugs for nongenomic targets [PtCl(O,O'‑acac)(L)] (L = dimethyl sulfoxide, DMSO; dimethyl sulfide, DMS), closely related to their very powerful organometallic analogues [Pt(O,O'-acac)(γ-acac)(L)], have been studied. [PtCl(O,O'-acac)(L)] and [Pt(O,O'-acac)(γ-acac)(L)] complexes were reported unreactive toward nucleobases. Aquo species [Pt(O,O'-acac)H₂O(L)]⁺, obtained from [PtCl(O,O'‑acac)(L)] by Ag⁺ driven coordinated Cl^– removal, gave access to [Pt(O,O'-acac)(L)(nucleoside)]⁺ ([Pt(O,O'-acac)(DMSO)(Guo)]⁺, [Pt(O,O'‑acac)(DMS)(Guo)]⁺, [Pt(O,O'-acac)(DMSO)(Ado)]⁺). The effect of the chelate oxygen donor acac (with respect to a chelate diammine), the role of the sulfur ligand (DMSO, DMS), and the influence of the purinic nucleoside itself on the coordinated Guo or Ado dynamic motions in [Pt(O,O'-acac)(L)(nucleoside)]⁺ complexes have been investigated by NMR spectroscopy. Interestingly, a slow rotation of nucleobase around the Pt–N(7) bond with formation of two rotamers was observed already at room temperature only in the case of [Pt(O,O'-acac)(DMSO)(Guo)]⁺. On the other hand, no hindered rotation at room temperature was detected in the analogous [Pt(O,O'-acac)(DMS)(Guo)]⁺ and [Pt(O,O'‑acac)(DMSO)(Ado)]⁺ complexes. Data suggest that rotation of the nucleoside in [Pt(O,O'-acac)(L)(nucleoside)]⁺ is very different with respect to the analogous [Pt(diammine)(L)(nucleoside)]²⁺ systems, due to specific interactions between the acac chelate ligand, the DMSO, and the nucleobase.