Preferred Conformation of Peptides Rich in Ac(8)c, a Medium-ring Alicyclic C-alpha,C-alpha-disubstituted Glycine
JOURNAL OF PEPTIDE SCIENCE(1996)
摘要
A complete series of terminally blocked, monodispersed homo-oligopeptides (to the pentamer level) from the sterically demanding, medium-ring alicyclic C-alpha,C-alpha-disubstituted glycine 1-aminocyclooctane-1-carboxylic acid (Ac(8)c), and two Ala/Ac(8)c tripeptides, were synthesized by solution methods and fully characterized. The preferred conformation of all the oligopeptides was determined in deuterochloroform solution by IR absorption and H-1-NMR. The molecular structures of the amino acid derivative Z-Ac(8)c-OH, the dipeptide pBrBz-(Ac(8)c)(2)-OH and the tripeptide pBrBz-(Ac(8)c)(3)-OtBu were assessed in the crystal state by X-ray diffraction. Conformational energy computations were performed on the monopeptide Ac-Ac(8)c-NHMe. Taken together, the results obtained strongly support the view that the Ac(8)c residue is an effective beta-turn and helix former. A comparison is also made with the conformational preferences of alpha-aminoisobutyric acid, the prototype of C-alpha,C-alpha-disubstituted glycines, and of the other members of the family of 1-aminocycloalkane-1-carboxylic acids (Ac(n)c, with n = 3, 5-7) investigated so far. The implications for the use of the Ac(8)c residue in peptide conformational design are considered.
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关键词
beta-bend,cyclic amino acid,3(10)-helix,peptide conformation,X-ray diffraction
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