Crystal Structures of Aza-β³-peptides, A New Class of Foldamers Relying on a Framework of Hydrazinoturns

Crystals of aza-β³-peptides have been obtained. This gives the first opportunity for hydrazino peptides, in the sense of oligomers built exclusively with α-hydrazinoacetic units, to be observed in the solid state. The structures make it clear that the H-bond network developed by aza-β³-peptides differs radically from those of the corresponding β³-peptides but strongly resembles that of the α-aminoxy peptides. Our study contributes to the current interest in hydrazino peptides as an extension of the β-peptide concept.