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 (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 - C-alpha cyclized) of their side chains.