Folding of peptides characterized by c3Val,a highly constrained analogue of valine |
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Authors: | Peggion Cristina Formaggio Fernando Crisma Marco Toniolo Claudio Jiménez Ana I Cativiela Carlos Kaptein Bernard Broxterman Quirinus B Saviano Michele Benedetti Ettore |
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Institution: | Institute of Biomolecular Chemistry, CNR, Department of Organic Chemistry, University of Padova, 35131 Padova, Italy. |
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Abstract: | 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. |
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Keywords: | amino acid synthesis β‐bend conformational analysis cyclopropane amino acid 310‐helix ir absorption NMR peptide synthesis x‐ray diffraction Cα‐tetrasubstituted α‐amino acids |
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