Crystal-state conformation of homo-oligomers of α-aminoisobutyric acid: Molecular and crystal structure of pBrBz-(Aib) 6 -OMe

A synthetic, terminally blocked homohexapeptide fromα-aminoisobutyric acid has been examined by single-crystal X-ray diffraction and the structure refined toR = 0.047. The compound is folded into almost two turns of a 310-helix, stabilized by four consecutive intramolecular N—H⋯·O=C H-bonds. An asymmetric covalent geometry for theα-aminoisobutyric acid residues, known to be responsible for the onset of the 310-helix in homopeptides from this Cα,α-dialkylatedα-aminoacid on the basis of a theoretrical conformational analysis, has been experimentally found also in this structure.