Synthesis of Sugar β-Amino Acid Containing Homooligomeric Cyclic Peptides

The synthesis of new cyclic peptides built from D-mannose-derived “anomeric” β3,3-aminoacids has been carried out using a solution-phase coupling methodology. Tetramers and hexamers in which the peptide backbone includes the anomeric carbon of the sugar are obtained and show perfect symmetry by nmr clearly indicating the occurrence of rapid interchanging conformers in solution. The lowest energy conformers obtained by molecular modelling suggest a bowl shape for the peptide backbone in which intramolecular hydrogen bonds between NH and CO of the amide group but also unusual hydrogen bonds involving the sugar ring oxygen could exist.