δ-Azaproline: A versatile tool to design pseudopeptides by its incorporation via Nε or Nδ atoms

Abstract δ-Azaproline, a bis-nitrogen proline, has been incorporated in pseudotripeptides of the type Xaa 1 -δazaPro-Xaa 3 . Peptide elongation via both nitrogen atoms has been explored by peptide coupling with glycine and/or alanine amino acids showing higher reactivity though an extra N δ atom compare to the native N e extremity. Carbonyls of some pseudopeptides have been converted into their thioanalogues. The conformational behavior of Gly-δazaPro-Gly tripeptide possessing thioamide linkages has been studied and compared with its carbonyl counterpart.