The title achiral peptide N-benzyloxycarbonyl-α-aminoisobutyryl-α-aminoisobutyryl-α-aminoisobutyrylglycine tert-butyl ester or Z-Aib-Aib-Aib-Gly-OtBu (Aib is α-aminoisobutyric acid, Z is benzyloxycarbonyl, Gly is glycine and OtBu indicates the tert-butyl ester), C26H40N4O7, is partly hydrated (0.075H2O) and 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 protection group and at the C-terminus. There are two 4→1 intramolecular hydrogen bonds.
Keywords: 310-helices; Z-Aib-Aib-Aib-Gly-OtBu; achiral peptides; crystal structure; hydrogen bonding; peptaibol antibiotic peptides; tetrapeptides; α-aminoisobutyric acid.