An oxazol-5(4H)-one from bezyloxycarbonyl-(Aib)4-OH

Benzyl N-[8-(4,4-dimethyl-5-oxo-4,5-dihydrooxazol-2-yl)-2,5,5,8-tetramethyl-3,6-dioxo-4,7-diazanon-2-yl]carbamate, C24H34N4O6, an oxazol-5(4H)-one from N-alpha-benzyloxycarbonyl-(Aib)(4)-OH (Aib = alpha-aminoisobutyryl) represents the longest peptide oxazolone so far characterized by X-ray diffraction. The overall geometry of the oxazolone ring compares well with literature data. The Aib(1) and Aib(2) residues are folded into a type III beta-bend, while the conformation adopted by Aib(3), preceding the oxazolone moiety, is semi-extended. The disposition of the oxazolone ring relative to the preceding residue is stabilized by C-H ... N and C-H ... O intramolecular interactions.