Cyclopenta[ d]isoxazoline β-Turn Mimics: Synthetic Approach, Turn Driving Force, Scope, and Limitations

ACS Omega. 2018 Oct 18;3(10):13551-13558. doi: 10.1021/acsomega.8b01670. eCollection 2018 Oct 31.

Abstract

Model β-turn inducers were prepared from constrained oxazanorbornene aminols. Taking advantage of the starting materials geometry, new diastereoisomeric compounds were synthesized, introducing different amino acidic residues. The products were spectroscopically characterized (VT and NMR titration). Temperature coefficients in dimethyl sulfoxide denote the existence of an intramolecular hydrogen bond. Chiroptical properties disclosed a β-turn arrangement of the synthesized compounds. The fused isoxazoline ring constraints the cyclopentane moiety, stabilizing a boatlike conformation that ensures the turn efficiency but limiting the accessibility to hindered amino acids.