title: Minor groove site coordination of adenine by platinum group metal ions: effects on basicity, base pairing, and electronic structure.
abstract: Dithioether- or diamine-tethered adenine derivatives react with Pt(II), Pd(II), and Rh(III) ions to give N3-coordinated complexes of the types [MCl(SSN)](+) (M = Pt or Pd), [RhCl(3)(SSN)], or [RhCl(3)(NNN)] (where SSN = 1-(N9-adenine)-3,6-dithia-heptane or 1-(N9-adenine)-4,7-dithia-octane; NNN = ethylenediamine-N,9-ethyladenine). Single-crystal X-ray analysis confirms the nature of the metal-nucleobase interaction and highlights a conserved intermolecular hydrogen-bonding motif for all the complexes, irrespective of the metal-ion geometry. Coordination significantly reduces the basicity of the adeninyl group, as indicated by a pK(a) value of -0.16 for [PtCl(N3-1-(N9-adenine)-3,6-dithia-heptane)]BF(4), compared to a pK(a) value of 4.2 for 9-ethyladenine. The site of proton binding, N1 or N7, could not be unambiguously assigned from the (1)H NMR data, because of the similar effect on the chemical shifts of the H2 and H8 protons. Density functional calculations at the BP-LACVP level suggest N1 as the site of protonation for this type of complex. This is in contrast to the N7-protonation reported for [Pt(dien)(N3-6,6',9-trimethyladenine)](2+), as reported elsewhere (Meiser et al., Chem.-Eur. J. 1997, 3, 388). However, further electronic structure calculations in the gas phase reveal that the preferred site for protonation for N3-bound complexes is conformationally dependent. N3 coordination was also found to reduce the extent of base pairing between adenine and thymine in dimethylsulfoxide for the self-complementary complex [PtCl(L3)](+) (L3 = 1-(N9-adenine)-3,6-dithia-9-(N1-thymine)nonane), compared to that for the uncomplexed ligand.
authors.affiliation: School of Natural Sciences: Chemistry, University of Newcastle upon Tyne, Newcastle upon Tyne, NE1 7RU, U.K.
authors.forename: David
authors.initials: D
authors.lastname: Amantia
authors.forename: Clayton
authors.initials: C
authors.lastname: Price
authors.forename: Michelle A
authors.initials: MA
authors.lastname: Shipman
authors.forename: Mark R J
authors.initials: MR
authors.lastname: Elsegood
authors.forename: William
authors.initials: W
authors.lastname: Clegg
authors.forename: Andrew
authors.initials: A
authors.lastname: Houlton
mesh_terms: D000225:Adenine / Q000031:analogs & derivatives* / Q000737:chemistry*; D001665:Binding Sites; D002614:Chelating Agents / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004563:Electrochemistry; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D015394:Molecular Structure; D009944:Organoplatinum Compounds / Q000737:chemistry*
chemical_list: D002614:Chelating Agents; D008024:Ligands; D009944:Organoplatinum Compounds; D000225:Adenine