Control of peptide conformation by the Thorpe-Ingold effect (C alpha-tetrasubstitution).
The preferred conformations of peptides heavily based on the currently extensively exploited achiral and chiral alpha-amino acids with a quaternary alpha-carbon atom, as determined by conformational energy computations, crystal-state (x-ray diffraction) analyses, and solution ((1)H-NMR and spectroscopic) investigations, are reviewed. It is concluded that 3(10)/alpha-helical structures and the fully extended (C(5)) conformation are preferentially adopted by peptide sequences characterized by this family of amino acids, depending upon overall bulkiness and nature (e.g., whether acyclic or C(alpha) (i) <--> C(alpha) (i) cyclized) of their side chains. The intriguing relationship between alpha-carbon chirality and bend/helix handedness is also illustrated. gamma-Bends and semiextended conformations are rarely observed. Formation of beta-sheet structures is prevented.
Toniolo
C
C
Department of Organic Chemistry, University of Padova, Institute of Biomolecular Chemistry, CNR, 35131 Padova, Italy. claudio.toniolo@unipd.it
Crisma
M
M
Formaggio
F
F
Peggion
C
C
D000596:Amino Acids / Q000737:chemistry*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D010455:Peptides / Q000737:chemistry*; D010456:Peptides, Cyclic / Q000737:chemistry; D011487:Protein Conformation; D017433:Protein Structure, Secondary
D000596:Amino Acids; D010455:Peptides; D010456:Peptides, Cyclic