Synthesis and evaluation of a (3R,6S,9S)-2-oxo-1-azabicyclo[4.3.0]nonane scaffold as a mimic of Xaa-trans-Pro in poly-L-proline type II helix conformation

We describe the development of a small-molecule mimic of Xaa-trans-Pro dipeptide in poly-L-proline type II helix conformation, based upon a (3R,6S,9S)-2-oxo-1-azabicyclo[4.3.0]nonane core structure. Stereoselective synthesis of the mimic from L-pyroglutamic acid is achieved in twelve linear steps and 9.9% yield. Configurational and conformational analyses are conducted using a combination of ¹H NMR spectroscopy, X-ray crystallography and circular dichroism spectroscopy; and evaluation of the mimic as a promising surrogate dipeptide, in a protein–protein interaction between the SH3 domain of human Fyn kinase (Fyn SH3) and peptidomimetics of its biological ligand, are conducted by ¹H-¹⁵N HSQC NMR titration experiments.