title: A topographically and conformationally constrained, spin-labeled, alpha-amino acid: crystallographic characterization in peptides.
abstract: 2,2,6,6-Tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid (TOAC) is a topographically and conformationally restricted, nitroxide containing, C(alpha)-tetrasubstituted alpha-amino acid. Here, we describe the molecular and crystal structures, as determined by X-ray diffraction analyses, of a TOAC terminally protected derivative, the cyclic dipeptide c(TOAC)(2).1,1,1,3,3,3-hexafluoropropan-2-ol (HFIP) solvate, and five TOAC-containing, terminally protected, linear peptides ranging in length from tetra- to hepta-peptides. Incipient and fully developed, regular or distorted 3(10)-helical structures are formed by the linear peptides. A detailed discussion on the average geometry and preferred conformation for the TOAC piperidine ring is also reported. The X-ray diffraction structure of an intramolecularly cyclized side product resulting from a C-activated TOAC residue has also been determined.
authors.affiliation: Department of Chemistry, Institute of Biomolecular Chemistry, CNR, University of Padova, 35131 Padova, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Crisma
authors.forename: J R
authors.initials: JR
authors.lastname: Deschamps
authors.forename: C
authors.initials: C
authors.lastname: George
authors.forename: J L
authors.initials: JL
authors.lastname: Flippen-Anderson
authors.forename: B
authors.initials: B
authors.lastname: Kaptein
authors.forename: Q B
authors.initials: QB
authors.lastname: Broxterman
authors.forename: A
authors.initials: A
authors.lastname: Moretto
authors.forename: S
authors.initials: S
authors.lastname: Oancea
authors.forename: M
authors.initials: M
authors.lastname: Jost
authors.forename: F
authors.initials: F
authors.lastname: Formaggio
authors.forename: C
authors.initials: C
authors.lastname: Toniolo
mesh_terms: D018360:Crystallography, X-Ray; D003497:Cyclic N-Oxides / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry*; D011487:Protein Conformation; D013113:Spin Labels
chemical_list: D003497:Cyclic N-Oxides; D010455:Peptides; D013113:Spin Labels; C037109:2,2,6,6-tetramethylpiperidine-N-oxide-4-amino-4-carboxylic acid