title: Preferred conformations of peptides containing tert-leucine, a sterically demanding, lipophilic alpha-amino acid with a quaternary side-chain Cbeta atom.
abstract: Terminally protected homopeptides of tert-leucine, from the dimer to the hexamer, co-oligopeptides of tert-leucine in combination with alpha-aminoisobutyric acid or glycine residues up to the hexamer level, and simple dipeptides representing known scaffolds for catalysts in asymmetric organic reactions were prepared by solution methods and fully characterized. The results of conformation analysis, performed by use of FT-IR absorption, NMR, CD, and X-ray diffraction techniques, indicate that this hydrophobic alpha-amino acid with tetrasubstitution at the Cbeta atom is structurally versatile. We show that it prefers extended or semiextended conformations, but can also be accommodated in folded structures, provided that these are biased by the presence of helicogenic residues. The current large-scale production of Tle, combined with its conformational preferences unravelled in this work, should make this bulky, hydrophobic, Calpha-trisubstituted alpha-amino acid a regular building block of any strategy seeking to tailor peptides with improved catalytic and pharmacological properties.
authors.affiliation: Institute of Biomolecular Chemistry, CNR, and Department of Chemistry, University of Padova, via Marzolo 1, 35131 Padova, Italy. fernando.formaggio@unipd.it
authors.forename: Fernando
authors.initials: F
authors.lastname: Formaggio
authors.forename: Chiara
authors.initials: C
authors.lastname: Baldini
authors.forename: Vittorio
authors.initials: V
authors.lastname: Moretto
authors.forename: Marco
authors.initials: M
authors.lastname: Crisma
authors.forename: Bernard
authors.initials: B
authors.lastname: Kaptein
authors.forename: Quirinus B
authors.initials: QB
authors.lastname: Broxterman
authors.forename: Claudio
authors.initials: C
authors.lastname: Toniolo
mesh_terms: D057927:Hydrophobic and Hydrophilic Interactions; D007930:Leucine / Q000031:analogs & derivatives; D008958:Models, Molecular; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry*; D017434:Protein Structure, Tertiary; D013057:Spectrum Analysis; D014633:Valine / Q000031:analogs & derivatives* / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D010455:Peptides; C089871:2-amino-3,3-dimethylbutanoic acid; D007930:Leucine; D014633:Valine