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

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