Isomer formation in the binding of [PtCl2(cis-cyclohexane-1,3-diamine)] to oligonucleotides and the X-ray crystal structure of [PtCl2(cis-cyclohexane-1,3-diamine)]·dimethylformamide†
作者:S. Tsuey Cham、Connie I. Diakos、Leanne T. Ellis、Ronald R. Fenton、Vivienne P. Munk、Barbara A. Messerle、Trevor W. Hambley
DOI:10.1039/b104502b
日期:——
The crystal structure of [PtCl2(cis-1,3-chxn)] (cis-1,3-chxn = (cis-cyclohexane-1,3-diamine)) as the dimethyformamide solvate is reported. When [PtCl2(cis-1,3-chxn)] binds to d(GpG), two isomers are formed that are readily separated by HPLC. Both the HPLC and GFAAS studies of the products show that the isomers form in a 1 ∶ 1 ratio. Competition experiments involving d(GpG) and the aquated and nonaquated forms of [PtCl2(cis-1,3-chxn)] and [PtCl2(NH3)2] showed that the slower binding of the former complex was due to slower aquation and not steric bulk. 1D and 2D NMR studies of the [Ptd(GpG)(cis-1,3-chxn)] isomers showed that both the dinucleotide and the diamine were highly fluxional, even at low temperatures, and this prevented formation of strong cross peaks in the NOESY and ROESY spectra and hence identification of the isomers. [PtCl2(cis-1,3-chxn)] was reacted with a 52-mer oligonucleotide having six GpG binding sites and the products were enzymatically digested and separated by HPLC. The two [Ptd(GpG)(cis-1,3-chxn)] stereoisomers were the only significant platinated products, again forming in a 1 ∶ 1 ratio although it had been anticipated that stereoselectivity would be observed in the reaction with the 52-mer because of the potential for steric interactions with the cis-1,3-chxn ligand. Molecular modelling revealed that the observed lack of stereoselectivity was due to the ability of the cis-1,3-chxn ligand to adopt a continuum of conformations that allow it to avoid severe steric clashes with the DNA.
报告了[PtCl2(cis-1,3-chxn)](cis-1,3-chxn = (cis-cyclohexane-1,3-diamine))二甲基甲酰胺溶液的晶体结构。当[PtCl2(cis-1,3-chxn)]与 d(GpG)结合时,会形成两种异构体,并很容易通过 HPLC 分离出来。对产物进行的 HPLC 和 GFAAS 研究表明,这两种异构体的形成比例为 1 ∶ 1。涉及 d(GpG)和[PtCl2(cis-1,3-chxn)]及[PtCl2(NH3)2]的含水和非含水形式的竞争实验表明,前一种复合物的结合速度较慢是由于含水速度较慢,而不是由于立体体积。对[Ptd(GpG)(cis-1,3-chxn)]异构体进行的一维和二维核磁共振研究表明,即使在低温下,二核苷酸和二胺都具有很强的通性,这阻碍了在 NOESY 和 ROESY 光谱中形成强交叉峰,从而无法识别异构体。[PtCl2(顺式-1,3-chxn)]与具有六个 GpG 结合位点的 52 聚合寡核苷酸反应,产物经酶消化后通过高效液相色谱分离。两种[Ptd(GpG)(cis-1,3-chxn)]立体异构体是唯一重要的板化产物,同样以 1 ∶ 1 的比例形成,尽管由于与顺式-1,3-chxn 配体可能发生立体相互作用,预计在与 52-mer 反应中会观察到立体选择性。分子模型显示,之所以观察到缺乏立体选择性,是因为顺式-1,3-chxn 配体能够采用连续的构象,从而避免与 DNA 发生严重的立体冲突。