title: NMR and X-ray structural characterization of a cisplatin analogue able to slow down the Pt-N7 rotation of a coordinated guanine base by a billion-fold times: 2,2'-bipiperidine(dimethylmalonato)platinum(II) complex.
abstract: The synthesis and the NMR and X-ray structural characterization of a cisplatin analogue designed to reduce the Pt-N7 rotation of a coordinated guanine base by a billion times are reported. The [Pt(dmm){(+/-)-bip}] (dmm=dimethylmalonato; bip=2,2'-bipiperidine) complex crystallizes in the C2/m space group, which contemplates a mirror plane bisecting the bip and dmm ligands. Because the bip moiety (R, R or S, S configuration at the 2,2'-carbon atoms) does not have planes of symmetry, the requirements of the crystal symmetry are satisfied by a statistical disorder made of bip molecules of R, R or S, S configurations alternating at the same crystallographic site. Such an unexpected arrangement has been permitted by a "quasi planarity" of the bip ligand [maximum deviation from the mean plane through the C and N atoms of 0.2927(9) A], which allows bip molecules of different chiralities to fit in the same space. The bip array of heavy atoms is overlaid, from both sides, by a layer of "quasi axial" (C)H and (N)H atoms (six per side). Those on one side are hydrogen-bonded to the dmm oxygen atoms of another complex molecule joined in a pair. The distance between the average platinum coordination planes is as short as 3.498(1) A, comparable to those found in crystals of the [PtCl 2(bipy)] complex (bipy=2,2'-bipyridine) and of graphite, in which, however, all atoms of each unit are rigorously coplanar and there are no out-of-plane hydrogen atoms. The NMR data show a net chemical shift separation between geminal methylene protons, with the "quasi axial" protons being always at higher field with respect to the "quasi equatorial" ones. This is in accordance with a rigid bip ligand frame and the inability of the bip methylene protons adjacent to the coordinated nitrogen to rotate away from a cis-G base (G=guanine) during G rotation around the Pt-N7 bond.
authors.affiliation: Dipartimento Farmaco-Chimico, Università di Bari, Bari, Italy.
authors.forename: Francesco P
authors.initials: FP
authors.lastname: Intini
authors.forename: Renzo
authors.initials: R
authors.lastname: Cini
authors.forename: Gabriella
authors.initials: G
authors.lastname: Tamasi
authors.forename: Michael B
authors.initials: MB
authors.lastname: Hursthouse
authors.forename: Giovanni
authors.initials: G
authors.lastname: Natile
mesh_terms: D002945:Cisplatin / Q000031:analogs & derivatives*; D018360:Crystallography, X-Ray; D004247:DNA / Q000737:chemistry; D006147:Guanine / Q000737:chemistry*; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D009584:Nitrogen / Q000737:chemistry*; D009944:Organoplatinum Compounds / Q000737:chemistry*; D010984:Platinum / Q000737:chemistry*; D012399:Rotation; D013237:Stereoisomerism
chemical_list: C530186:2,2'-bipiperidine(dimethylmalonato)platinum(II); D008024:Ligands; D009944:Organoplatinum Compounds; D010984:Platinum; D006147:Guanine; D004247:DNA; D009584:Nitrogen; D002945:Cisplatin