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Synthesis of 1,2-Azaborines and the Preparation of Their Protein Complexes with T4 Lysozyme Mutants
Published on: March 25, 2017
Aza-beta3-cyclohexapeptides: pseudopeptidic macrocycles with interesting conformational and configurational
Philippe Le Grel1, Arnaud Salaün, Michel Potel
1ICMV, UMR CNRS 6226, Université de Rennes I, 263 avenue du Général Leclerc 35042 Rennes Cedex, France. philippe.legrel@univ-rennes1.fr
Abstract:
Among pseudopeptidic foldamers, aza-beta3-peptides have the unique property to possess nitrogen stereocenters instead of carbon stereocenters. As the result of pyramidal inversion at N(alpha)-atoms along the backbone, they behave as a set of C8-based secondary structures in equilibrium. This structural modulation is exploited here to prepare 24-membered macrocycles with great efficiency. Both crystal structures and spectroscopic data establish that aza-beta3-cyclohexapeptides adopt a highly organized conformation where the relative configuration of chiral nitrogen atoms is alternated. This makes them an interesting scaffold as the stereocontrol occurs spontaneously through the cyclization. These compounds reveal an unprecedented slow pyramidal nitrogen inversion in macrocycles. Pyramidal ground state stabilization, hindered rotation, steric crowding, and H-bond cooperativity are proposed to participate in this striking phenomenon. The equilibrium between invertomers of aza-beta3-cyclohexapeptides is reminiscent of the interchange between the two chair forms of cyclohexane.
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