title: Stereochemistry of peptides containing 1-aminocycloheptane-1-carboxylic acid (Ac7c).
abstract: The crystal structures of four peptides incorporating 1-aminocycloheptane-1-carboxylic acid (Ac7c) are described. Boc-Aib-Ac7c-NHMe and Boc-Pro-Ac7c-Ala-OMe adopt beta-turn conformations stabilized by an intramolecular 4----1 hydrogen bond, the former folding into a type-I/III beta-turn and the latter into a type-II beta-turn. In the dipeptide esters, Boc-Aib-Ac7c-OMe and Boc-Pro-Ac7c-OMe, the Ac7c and Aib residues adopt helical conformations, while the Pro residue remains semi-extended in both the molecules of Boc-Pro-Ac7c-OMe found in the asymmetric unit. The cycloheptane ring of Ac7c residues adopts a twist-chair conformation in all the peptides studied. 1H-NMR studies in CDCl3 and (CD3)2SO and IR studies in CDCl3 suggest that Boc-Aib-Ac7c-NHMe and Boc-Pro-Ac7c-Ala-OMe maintain the beta-turn conformations in solution.
authors.affiliation: Department of Organic Chemistry, University of Padova, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Valle
authors.forename: M
authors.initials: M
authors.lastname: Crisma
authors.forename: C
authors.initials: C
authors.lastname: Toniolo
authors.lastname: Sudhanand
authors.forename: R B
authors.initials: RB
authors.lastname: Rao
authors.forename: M
authors.initials: M
authors.lastname: Sukumar
authors.forename: P
authors.initials: P
authors.lastname: Balaram
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry; D000598:Amino Acids, Cyclic; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000737:chemistry*; D011487:Protein Conformation; D013055:Spectrophotometry, Infrared; D013237:Stereoisomerism; D014961:X-Ray Diffraction
chemical_list: D000596:Amino Acids; D000598:Amino Acids, Cyclic; D009842:Oligopeptides; C014965:1-aminocycloheptanecarboxylic acid