No abstract

Herein, we present a novel synthetic strategy, to amino-acid-free peptide synthesis based on postpolymerization conversion, for chiral nonnatural polypeptides. Optically active poly-N-alkoxyamides were prepared by our asymmetric polymerization as precursors of polypeptides, and the reductive cleavage of N–O bonds using a SmI2–THF complex was carried out. The reaction proceeded smoothly with quantitative conversion to afford a nonnatural polypeptide. The resulting polypeptide adopted a one-handed stable helical structure in solution, which was established by circular dichroism (CD) and theoretical calculations using density functional theory (DFT). The simulated spectra by time-dependent (TD) DFT methods clearly indicated the validity of the proposed structure. The synthetic approach is a promising candidate for the synthesis of nonnatural polypeptides.

A methodology for producing dual structural systems of macromolecules, which involves flipping the unsymmetrical aromatic rings on the main chain is presented. Previously, we reported a non-natural polypeptide containing an aromatic ring on the peptide backbone, called a poly “arylopeptide”. Herein, we used 2,6-naphthalene rings as axially unsymmetrical spacers, which has two geometrical isomers, anti and syn, to create dual structural properties. The miniscule energy difference between the two geometrical isomers can be amplified by incorporating the 2,6-naphthylene units into the polypeptide backbone, which creates a thermodynamic driving force for the formation of two specific global structures (i.e., 31-helix or 41-helix) biased toward one side geometrical isomer depending on the side chain. Additionally, the 31-helix can be switched to the 41-helix upon addition of a small amount of additives, indicating a conformational conversion from an identical sequence. The developmental dual helical systems exploit basic molecular geometry and can serve as a design platform for synthetic polymers.

Asymmetric polymerization is a promising method for constructing sophisticated backbones that contain asymmetric carbons on the main chain. Herein, we report the precise design and synthesis of a novel polymer...