organic compounds
A peptide is reported which is a left-handed helix with a right-handed conformation in the fourth residue, which is the only chiral residue. There are two 4→1 intramolecular hydrogen bonds. In the crystal structure, molecules are linked by hydrogen bonds along the c axis.
research papers
The achiral tetrapeptide Z-Aib-Aib-Aib-Gly-OtBu has two different conformations which together constitute the asymmetric unit. Both molecules form incipient 310-helices. They differ in the relative orientation of the N-terminal protecting group and at the C-terminus. There are two 4→1 intramolecular hydrogen bonds.