β NO Turns and Helices Induced by β 2 ‐Aminoxy Peptides: Synthesis and Conformational Studies

Herein, we report an efficient route for the asymmetric synthesis of β 2 ‐aminoxy acids as well as experimental and theoretical studies of conformations of peptides composed of β 2 ‐aminoxy acids. The nine‐membered‐ring intramolecular hydrogen bonds, namely, β NO turns, are generated between adjacent residues in those peptides, in accordance with our computational results. The presence of two consecutive homochiral β NO turns leads to the formation of β NO helical structures in solution, although both helical (composed of two β NO turns of the same handedness) and reverse‐turn (composed of two β NO turns with opposite handedness) structures are of similar stability, as suggested by theoretical studies. Nevertheless, two slightly different conformations, with the same handedness, of β 2 ‐aminoxy monomers have been observed in the solid state and in solution according to our X‐ray and 2D NOESY studies. magnified image