title: Defect peptide chemistry: perturbations in the structure of a homopentapeptide induced by a guest residue interrupting side-chain regularity.
abstract: The fully blocked pentapeptide Tfa-(Deg)2-L-Abu-(Deg)2-OtBu (Tfa: triflouroacetyl; Deg: C alpha, alpha-diethylglycine; Otbu: tert-butoxy) adopts in the crystal state a regular, right-handed 3(10)-helical structure stabilized by three N--H...O=C intramolecular 1 < 4 (or C10) H bonds, as determined by an x-ray diffraction analysis. However, a Fourier transform ir absorption and 1H-nmr study strongly supports the view that in deuterochloroform solution the four Deg residues at both termini of the peptide main chain are involved in successive, fully extended C5 forms. A comparison with the stable, fully developed, multiple C5 conformation of Tfa-(Deg)5-OtBu indicates that incorporation of an Abu guest residue, interrupting the side-chain uniformity of the host (Deg)5 homopeptide, while altering only marginally the conformation in a solvent of low polarity, is responsible for a dramatic perturbation of the crystal-state structure.
authors.affiliation: CNR, Department of Chemistry, University of Naples Federico II, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Benedetti
authors.forename: C
authors.initials: C
authors.lastname: Pedone
authors.forename: V
authors.initials: V
authors.lastname: Pavone
authors.forename: B
authors.initials: B
authors.lastname: Di Blasio
authors.forename: M
authors.initials: M
authors.lastname: Saviano
authors.forename: R
authors.initials: R
authors.lastname: Fattorusso
authors.forename: M
authors.initials: M
authors.lastname: Crisma
authors.forename: F
authors.initials: F
authors.lastname: Formaggio
authors.forename: G M
authors.initials: GM
authors.lastname: Bonora
authors.forename: C
authors.initials: C
authors.lastname: Toniolo
mesh_terms: D000595:Amino Acid Sequence; D018360:Crystallography, X-Ray; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000737:chemistry*; D011487:Protein Conformation
chemical_list: D009842:Oligopeptides