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<p>“Peptoids” was proposed, over decades ago, as a term describing analogs of peptides that exhibit
better physicochemical and pharmacokinetic properties than peptides. Oligo-(N-substituted glycines)
(oligo-NSG) was previously proposed as a peptoid due to its high proteolytic resistance and membrane permeability. However, oligo-NSG is conformationally flexible and is difficult to achieve a
defined shape in water. This conformational flexibility is severely limiting biological application of
oligo-NSG. Here, we propose oligo-(N-substituted alanines) (oligo-NSA) as a new peptoid that
forms a defined shape in water. A synthetic method established in this study enabled the first isolation and conformational study of optically pure oligo-NSA. Computational simulations, crystallographic studies and spectroscopic analysis demonstrated the well-defined extended shape of oligo-NSA realized by backbone steric effects. The new class of peptoid achieves the constrained conformation without any assistance of N-substituents and serves as an ideal scaffold for displaying
functional groups in well-defined three-dimensional space, which leads to effective biomolecular
recognition.
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