Novel conformationally restricted glycoamino acids from glyco-α-aminonitriles as potent turn mimics in peptide synthesis

Our previously described glycoaminocyanation procedure using Ti(OiPr)4 and TMSiCN has been applied to introduce amino acid and peptide moieties on a monosaccharide. Selective reduction using NaNH4–CoCl2 and Pd(C), respectively, is described. Restricted conformation of the new glycoamino acids favours intramolecular cyclisation to give the corresponding oxopiperazine 5a–b and 12a–b. The target acyclic compound I was obtained when the peptide derivative was displaced from the complex using KCN. Hydrolysis of the glycospirohydantoin 18 to give the glycoamino acid II is also described.