Peptoids are oligomers of N-substituted glycine units. N-substitution improves cell-permeability of peptoids and enhance their proteolytic stability over natural peptides. However, most peptoid ligands discovered so far possess moderate affinity towards their biological targets, which is linked to their conformational flexibility that causes substantial entropic loss during the peptoid-biomacromolecule binding process. One of the major cause of conformational flexibility of peptoids is the facile cis-trans isomerization of their tertiary amide bonds. In recent years, many investigators have shown that the incorporation of specific side chains with unique steric and stereoelectronic features can favorably shift the cis-trans equilibrium of peptoids towards one of the two isomeric forms. In this review, we have discussed the strategies developed over the years to control the cis-trans isomerization of peptoid amide bonds.
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