A novel peptide conformation: First unequivocal observation of the oxy‐analog of a β‐bend

The x‐ray diffraction analysis of the N‐benzyloxycarbonyl homo‐tripeptide from α‐amino‐isobutyric acid has shown the occurrence of an incipient 310‐helix characterized by one type‐III (or type‐III′) β‐bend followed by one oxy‐analog of the same type of β‐bend. This represents the first unequivocal observation of the latter conformation, where the O—H group of the COOH moiety present at the C‐terminus of the peptide main chain plays the role of the hydrogen‐bonding donor. These results have been compared with those of the same peptide in its monohydrate form and of its methyl ester derivative, the x‐ray diffraction structures of which are also described here.