Folding of peptides characterized by c3Val, a highly constrained analogue of valine.
Using a combined chemical/chiral chromatographic approach we synthesized an N-protected derivative of (R)-c(3)Val, a severely conformationally restricted C(alpha)-tetrasubstituted alpha-amino acid characterized by a C(beta,beta)-dimethylated cyclopropane system. A set of terminally protected derivatives and model peptides (to the heptamer level), containing one or two (R)-c(3)Val residues in combination with either Aib or Gly residues, was prepared by solution methods. A detailed solution and crystal-state conformational investigation, based on Fourier transform infrared (FTIR) absorption, (1)H-NMR, and x-ray diffraction techniques, performed in comparison with a similar study on related derivatives and peptides rich in (alphaMe)Val, the prototype of C(alpha)-tetrasubstituted alpha-amino acids of this subfamily, allowed us to conclude the following: (a) c(3)Val is a good beta-bend and helix former, although less efficient than (alphaMe)Val. (b) The relationship between alpha-carbon chirality and screw sense of the folded structure formed is the same as that of (alphaMe)Val, i.e., the (R)-enantiomer has a strong left-handed bias. (c) c(3)Val seems more prone than (alphaMe)Val to fold into a gamma-bend conformation. The conformational propensities of C(beta,beta)-disubstituted Ac(3)c residues are also discussed in comparison with those of the parent cyclopropane residue.
Peggion
Cristina
C
Institute of Biomolecular Chemistry, CNR, Department of Organic Chemistry, University of Padova, 35131 Padova, Italy.
Formaggio
Fernando
F
Crisma
Marco
M
Toniolo
Claudio
C
Jiménez
Ana I
AI
Cativiela
Carlos
C
Kaptein
Bernard
B
Broxterman
Quirinus B
QB
Saviano
Michele
M
Benedetti
Ettore
E
D018360:Crystallography, X-Ray; D008958:Models, Molecular; D008968:Molecular Conformation; D009842:Oligopeptides / Q000138:chemical synthesis / Q000737:chemistry; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism*; D011487:Protein Conformation; D017510:Protein Folding; D014633:Valine / Q000031:analogs & derivatives* / Q000737:chemistry*; D014961:X-Ray Diffraction
D009842:Oligopeptides; D010455:Peptides; D014633:Valine