Pt II coordination to N1 of 9-methylguanine: Why it facilitates binding of additional metal ions to the purine ring

Barbara Müller, Wei Zheng Shen, Pablo J. Sanz Miguel, Francisca M. Albertí, Tushar Van Der Wijst, Marc Noguera, Luis Rodríguez-Santiago, Mariona Sodupe, Bernhard Lippert

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Abstract

The preparation and X-ray crystal structure analysis of {trans-[Pt(MeNH 2) 2(9-MeG-N1) 2]}·{3 K 2[Pt(CN) 4]}·6 H 2O (3 a) (with 9-MeG being the anion of 9-methylguanine, 9-MeGH) are reported. The title compound was obtained by treating [Pt(dien)(9-MeGH-N7)] 2+ (1; dien=diethylenetriamine) with trans-[Pt(MeNH 2) 2(H 2O) 2] 2+ at pH 9.6, 60 °C, and subsequent removal of the [(dien)Pt II] entities by treatment with an excess amount of KCN, which converts the latter to [Pt(CN) 4] 2-. Cocrystallization of K 2[Pt(CN) 4] with trans-[Pt(MeNH 2) 2(9-MeG-N1) 2] is a consequence of the increase in basicity of the guanine ligand following its deprotonation and Pt coordination at N1. This increase in basicity is reflected in the pK a values of trans-[Pt(MeNH 2) 2(9-MeGH-N1) 2] 2+ (4.4±0.1 and 3.3±0.4). The crystal structure of 3 a reveals rare (N7,O6 chelate) and unconventional (N2,C2,N3) binding patterns of K + to the guaninato ligands. DFT calculations confirm that K + binding to the sugar edge of guanine for a N1-platinated guanine anion is a realistic option, thus ruling against a simple packing effect in the solid-state structure of 3 a. The linkage isomer of 3 a, trans-[Pt(MeNH 2) 2(9-MeG-N7) 2] (6 a) has likewise been isolated, and its acid-base properties determined. Compound 6 a is more basic than 3 a by more than 4 log units. Binding of metal entities to the N7 positions of 9-MeG in 3 a has been studied in detail for [(NH 3) 3Pt II], trans-[(NH 3) 2Pt II], and [(en)Pd II] (en=ethylenediamine) by using 1H NMR spectroscopy. Without exception, binding of the second metal takes place at N7, but formation of a molecular guanine square with trans-[(Me 2NH 2)Pt II] cross-linking N1 positions and trans-[(NH 3) 2Pt II] cross-linking N7 positions could not be confirmed unambiguously, despite the fact that calculations are fully consistent with its existence. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Original languageEnglish
Pages (from-to)9970-9983
JournalChemistry - A European Journal
Volume17
Issue number36
DOIs
Publication statusPublished - 29 Aug 2011

Keywords

  • bioinorganic chemistry
  • guanine
  • nucleobases
  • platinum
  • transition metals

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