Promotion of 11/9‐helical folding in α/β‐peptides containing β2‐homoalanine residue

The 11/9‐helix is one of nontraditional helices available to α/β‐peptides with alternating residue types. Several β‐amino acid residues are known to promote 11/9‐helical folding with two types of intramolecular hydrogen bonds. Both β2‐amino acids and β3‐amino acids are common acyclic β‐amino acids that can be regarded as homologs of α‐amino acids with the same side chain group. However, β2‐amimo acids have not been widely used as much as β3‐amino acids partly because β2‐residue is believed to be not as strong as β3‐residue in promoting a distinct conformation. Here we report 11/9‐helical folding of α/β‐peptides that consist of L‐α‐alanine and (S)‐β2‐homoalanine with residue alternation. In addition, circular dichroism study reveals that β2‐homoalanine promotes 11/9‐helical folding more strongly than β3‐homoalanine in polar protic solvent conditions.