title: Synthesis and conformational studies of peptides containing TOAC, a spin-labelled C alpha, alpha-disubstituted glycine.
abstract: A variety of host L-alanine homo-peptides (to the pentamer) containing one or two spin-labelled TOAC (2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid) residues were synthesized by solution methods and fully characterized. The conformational features of the terminally blocked, doubly spin-labelled TOAC-(Ala)2-TOAC-Ala-pentapeptide were examined in the crystal state by X-ray diffraction and in solution using a combination of techniques (Fourier transform infrared, circular dichroism, cyclic voltammetry and electron spin resonance) in comparison with singly labelled shorter peptides. The 3(10)-helical structure of the pentapeptide, promoted by the two C alpha, alpha-disubstituted glycines under favourable experimental conditions, allows an interaction to take place between the two nitroxide TOAC side chains spaced by one turn of the helix. Taken together, these results suggest that TOAC is an excellent probe for exploring bends and helices in doubly labelled peptides.
authors.affiliation: Department of Organic Chemistry, University of Padova, Italy.
authors.forename: C
authors.initials: C
authors.lastname: Toniolo
authors.forename: E
authors.initials: E
authors.lastname: Valente
authors.forename: F
authors.initials: F
authors.lastname: Formaggio
authors.forename: M
authors.initials: M
authors.lastname: Crisma
authors.forename: G
authors.initials: G
authors.lastname: Pilloni
authors.forename: C
authors.initials: C
authors.lastname: Corvaja
authors.forename: A
authors.initials: A
authors.lastname: Toffoletti
authors.forename: G V
authors.initials: GV
authors.lastname: Martinez
authors.forename: M P
authors.initials: MP
authors.lastname: Hanson
authors.forename: G L
authors.initials: GL
authors.lastname: Millhauser
mesh_terms: D002942:Circular Dichroism; D018360:Crystallography, X-Ray; D003497:Cyclic N-Oxides / Q000737:chemistry*; D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D008958:Models, Molecular; D009842:Oligopeptides / Q000138:chemical synthesis* / Q000737:chemistry*; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D012996:Solutions; D013053:Spectrophotometry; D017550:Spectroscopy, Fourier Transform Infrared; D013113:Spin Labels
chemical_list: D003497:Cyclic N-Oxides; D009842:Oligopeptides; D012996:Solutions; D013113:Spin Labels; C037109:2,2,6,6-tetramethylpiperidine-N-oxide-4-amino-4-carboxylic acid