Heterogeneous H‑Bonding in a Foldamer Helix

Structural
characterization of new α/γ-peptide foldamers
containing the cyclically constrained γ-amino acid I is described. Crystallographic and 2D NMR analysis shows that γ
residue I promotes the formation of a 12/10-helical secondary
structure in α/γ-peptides. This helix contains two different
types of internal H-bond, and the data show that the 12-atom CO­(i) → H–N­(i+3) H-bond is more
favorable than the 10-atom CO­(i) →
H–N­(i–1) H-bond. Several foldamer helices
featuring topologically distinct H-bonds have been discovered, but
our findings are the first to show that such H-bonds may differ in
their favorability.