Conformational flexibility within the chelate rings of [Pt(en)(CBDCA-O,O′)], an analogue of the antitumour drug carboplatin:: X-ray crystallographic and solid-state NMR studies

The X-ray crystal structure of [Pt(en)(CBDCA-O,O')] 1, an analogue of the anticancer drug carboplatin, shows that platinum has an approximate square-planar coordination. The crystals are orthorhombic with space group Pnma. The Pt-CBDCA chelate ring adopts a flattened-boat conformation, similar to that found for carboplatin, and the Pt-ethylenediamine chelate ring exhibits both delta and lambda conformations with equal populations. Ethylenediamine chelate ring inversion was observed by C-13 CP/MAS NMR spectroscopy The exchange rate and the activation free energy (Delta G double dagger) at 317 K were determined to be ca. 415 s(-1) and 62 kJ mol(-1), respectively. The CBDCA ligand appears to have a direct effect on the dynamics of the en ring. Conformational flexibility of the CBDCA ring is also discussed. Such dynamic processes within chelated platinum complexes could play a role in the biological recognition of anticancer complexes.