The non protonable reduced aza-peptide fragment

Article abstract of DOI:10.1016/S0040-4039(97)00410-3

The reduced aza-peptide fragment (C(α)-CH₂-NH-N(α)R-CO-NH-C(α)) is obtained by reduction of the semicarbazone moiety (C(α)-CH=N-N(α)R-CO-NH-C(α)) in an imino aza-peptide. It differs from the aminomethylene link (C(α)-CH₂-NH-C(α)HR-CO-NH-C(α)) found in the reduced peptides by the absence of protonation in water in the 2-12 pH range. The reduced aza-analogue of the Pro-Ala dipeptide has been studied in solution by ¹H-NMR and IR spectroscopy, and in the solid state by X-ray diffraction. Its structure is guile similar to that of the neutral reduced dipeptide analogue in solution.