Conformational isomerism in cyclic peptoids and its specification

Most of the structural studies made on the secondary structure of peptoids describe their geometric attributes in terms of the classic Ramachandran plot (based on the local analysis of ω, ψ, χ, φ dihedral angles). However, little intuitive understanding is available from internal coordinates when st...

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Bibliographic Details
Published in:Organic & biomolecular chemistry 2017, Vol.15 (46), p.9932-9942
Main Authors: D'Amato, A, Schettini, R, Della Sala, G, Costabile, C, Tedesco, C, Izzo, I, De Riccardis, F
Format: Article
Language:English
Subjects:
Alcohols
Angles (geometry)
Asymmetric synthesis
Chemical synthesis
Chirality
Crystallography
Magnetic resonance spectroscopy
NMR
NMR spectroscopy
Nuclear magnetic resonance
Protein structure
Secondary structure
Stereochemistry
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Summary:Most of the structural studies made on the secondary structure of peptoids describe their geometric attributes in terms of the classic Ramachandran plot (based on the local analysis of ω, ψ, χ, φ dihedral angles). However, little intuitive understanding is available from internal coordinates when stereochemistry is involved. In this contribution we list all the conformationally stable cyclic peptoids reported up to the year 2017 and propose a simple method to define their geometric arrangement in terms of planar chirality. Evidence of conformational isomerism (due to the long average time of single bond rotation) and conformational chirality (induced by the absence of roto-reflection axes) in this promising class of synthetic macrocycles is provided by NMR spectroscopy (using Pirkle's alcohol as chiral solvating agent) and careful evaluation of X-ray crystallographic studies. The full understanding of the oligomeric macrocycles' structural properties and the clear framing of their conformational isomerism in a proper conceptual scheme is fundamental for future application of peptoids in asymmetric synthesis, chiral recognition and supramolecular chemistry.
ISSN:1477-0520
1477-0539
DOI:10.1039/c7ob02643a