Control of peptide conformation by the Thorpe-Ingold effect (C alpha-tetrasubstitution).

TLDR: The preferred conformations of peptides heavily based on the currently extensively exploited achiral and chiral α-amino acids with a quaternary α-carbon atom, as determined by conformational energy computations, crystal-state (x-ray diffraction) analyses, and solution (1H-NMR and spectroscopic) investigations, are reviewed in this paper.

Abstract: The preferred conformations of peptides heavily based on the currently extensively exploited achiral and chiral α-amino acids with a quaternary α-carbon atom, as determined by conformational energy computations, crystal-state (x-ray diffraction) analyses, and solution (1H-NMR and spectroscopic) investigations, are reviewed. It is concluded that 310/α-helical structures and the fully extended (C5) 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 ↔ C cyclized) of their side chains. The intriguing relationship between α-carbon chirality and bend/helix handedness is also illustrated. γ-Bends and semiextended conformations are rarely observed. Formation of β-sheet structures is prevented. © 2002 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 60: 396–419, 2001