Unique β-Turn Peptoid Structures and Their Application as Asymmetric Catalysts.

Peptoids, N-substituted glycine oligomers, represent an important class of peptidomimetics that can fold into three-dimensional structures in solution. Most of the folded peptoid structures, however, resemble helices, and this can limit their applications, specifically in asymmetric catalysis. In this work, for the first time, unique examples of pyrrolidine-based β-turn-like peptoids are described and characterized, both in the solid state, by single-crystal X-ray analysis, and in solution, by circular dichroism spectroscopy. Furthermore, their highly efficient and enantioselective catalytic activity for the production of γ-nitro aldehydes by asymmetric Michael reaction in water was demonstrated. The structural properties and DFT-D3 calculations of the new β-turn-like peptoids, as well as catalytic and spectroscopic studies on designed pyrrolidine-based helical peptoids, suggest that the β-turn structure plays a key role in the stereoselectivity of the catalytic reaction.