title: Hybridization of long pyridine-dicarboxamide oligomers into multi-turn double helices: slow strand association and dissociation, solvent dependence, and solid state structures.
abstract: Oligoamides of 2,6-diaminopyridine and 2,6-pyridinedicarboxylic acid comprised of 5, 7, 9, 11, or 13 units and bearing 4-isobutoxychains on all pyridine rings and tert-butyl-carbamate terminal groups have been synthesized stepwise, along with an 11 mer having benzyl-carbamate terminal groups. The crystal structure of all five Boc-terminated compounds has been obtained and shows a highly regular and conserved double helical hybridization motif of up to 3 complete turns for the 13 mer. Four pyridine units span one helical turn and define a helix pitch of ca 7 A. Solution studies in CDCl(3) demonstrated that the Boc-terminated oligomers strongly hybridize in this solvent, and that K(dim) values increase with oligomer length. The K(dim) values are 31000 and 7 x 10(5) L mol(-1) for the 7 mer and the 9 mer, respectively, and are too high to be measured by NMR for the 11 mer and the 13 mer. Hybridization and dissociation kinetics at 2 mM proceed at decreasing rates upon increasing oligomer length. The rate was faster than minutes for the 7 mer, of the order of hours for the 9 mer, and days for the 11 mer and 13 mer. The same trend was observed in [D(5)]pyridine but with considerably lower K(dim) values and faster kinetics. The benzylcarbamate 11 mer was also found to hybridize into a double helix but with reduced K(dim) values and faster kinetics compared to its Boc-terminated analogue. Combined with previous studies, the results presented here frame a global understanding of the hybridization of these pyridinecarboxamide oligomers and provide useful guidelines for the design of other artificial double helices.
authors.affiliation: Université Victor Ségalen Bordeaux 2, EA 4138-Pharmacochimie, 146 rue Léo Saignat, 33076 Bordeaux Cedex, France.
authors.forename: Benoit
authors.initials: B
authors.lastname: Baptiste
authors.forename: Jiang
authors.initials: J
authors.lastname: Zhu
authors.forename: Debasish
authors.initials: D
authors.lastname: Haldar
authors.forename: Brice
authors.initials: B
authors.lastname: Kauffmann
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Léger
authors.forename: Ivan
authors.initials: I
authors.lastname: Huc
mesh_terms: D001704:Biopolymers / Q000737:chemistry*; D018360:Crystallography, X-Ray; D019281:Dimerization; D007700:Kinetics; D008958:Models, Molecular; D008968:Molecular Conformation; D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular; D011725:Pyridines / Q000737:chemistry*
chemical_list: D001704:Biopolymers; D011725:Pyridines