Induction of Unexpected Left-Handed Helicity by an N-Terminal L-Amino Acid in an Otherwise Achiral Peptide Chain

Peptide helices containing L‐amino acids are typically right‐handed. Exceptions are peptide helices containing the achiral amino acids 2‐aminoisobutyric acid and glycine with a single chiral amino acid at the N terminus. These helices are left‐handed when the N‐terminal residue is a common tertiary proteinogenic amino acid, such as L‐valine (see picture, left), but right‐handed when the N‐terminal residue is the quaternary amino acid L‐α‐methylvaline (right).