National Center for Biomolecular Research, Faculty of Science and Central European Institute of Technology-CEITEC, Masaryk University, Kamenice 5/A4, CZ-62500 Brno, Czech Republic.
Inorg Chem. 2012 Feb 6;51(3):1371-9. doi: 10.1021/ic201595e. Epub 2012 Jan 19.
Two novel Pt(IV) complexes of aromatic cytokinins with possible antitumor properties were prepared by reaction of selected aminopurines with K(2)PtCl(6). The structures of both complexes, 9-[6-(benzylamino)purine] pentachloroplatinate (IV) and 9-[6-(furfurylamino)purine] pentachloroplatinate (IV), were characterized in detail by using two-dimensional NMR spectroscopy ((1)H, (13)C, (15)N, and (195)Pt) in solution and CP/MAS NMR techniques in the solid state. We report for the first time the X-ray structure of a nucleobase adenine derivative coordinated to Pt(IV) via the N9 atom. The protonation equilibria for the complexes in solution were characterized by using NMR spectroscopy (isotropic chemical shifts and indirect nuclear spin-spin coupling constants) and the structural conclusions drawn from the NMR analysis are supported by relativistic density-functional theory (DFT) calculations. Because of the presence of the Pt atom, hybrid GGA functionals and scalar-relativistic and spin-orbit corrections were employed for both the DFT calculations of the molecular structure and particularly for the NMR chemical shifts. In particular, the populations of the N7-protonated and neutral forms of the complexes in solution were characterized by correlating the experimental and the DFT-calculated NMR chemical shifts. In contrast to the chemical exchange process involving the N7-H group, the hydrogen atom at N3 was determined to be unexpectedly rigid, probably because of the presence of the stabilizing intramolecular interaction N3-H···Cl. The described methodology combining the NMR spectroscopy and relativistic DFT calculations can be employed for characterizing the tautomeric and protonation equilibria in a large family of transition-metal-modified purine bases.
两种具有潜在抗肿瘤特性的芳香族细胞激动素的新型 Pt(IV) 配合物是通过选择的氨基嘌呤与 K(2)PtCl(6) 反应制备的。两种配合物，9-[6-(苄基氨基)嘌呤]五氯合铂(IV)和 9-[6-(糠基氨基)嘌呤]五氯合铂(IV)的结构均通过二维 NMR 光谱（溶液中的 (1)H、(13)C、(15)N 和 (195)Pt）和固态 CP/MAS NMR 技术进行了详细表征。我们首次报道了通过 N9 原子与 Pt(IV) 配位的碱基腺嘌呤衍生物的 X 射线结构。通过 NMR 光谱（各向同性化学位移和间接核自旋-自旋耦合常数）和 NMR 分析得出的结构结论来表征配合物在溶液中的质子化平衡，从 NMR 分析得出的结构结论得到了相对论密度泛函理论（DFT）计算的支持。由于 Pt 原子的存在，混合 GGA 泛函和标量相对论和自旋轨道修正都用于分子结构的 DFT 计算，特别是对于 NMR 化学位移。特别是，通过关联实验和 DFT 计算的 NMR 化学位移，确定了溶液中配合物的 N7-质子化和中性形式的分布。与涉及 N7-H 基团的化学交换过程相反，N3 上的氢原子被确定为出乎意料的刚性，这可能是由于存在稳定的分子内相互作用 N3-H···Cl。这种结合 NMR 光谱和相对论 DFT 计算的方法可用于表征大量过渡金属修饰的嘌呤碱基的互变异构和质子化平衡。
