H-bonding directed one-step synthesis of novel macrocyclic peptides from ε-aminoquinolinecarboxylic acid

Two macrocyclic peptides 1a and 1b were synthesized directly from ε-aminoquinolinecarboxylic acid 2a and 2b, respectively. The preorganization of the uncyclized intermediates mediated by hydrogen bonding assisted the cyclization. The structures of 1a and 1b were characterized by 1H and 13C NMR spectroscopy and MALDI-TOF MS analysis. Solid state structure of 1a was investigated by single crystal X-ray studies. Their aggregation behaviors in solution were studied by both variable concentration and temperature 1H NMR experiments.