Peptoid
Peptoids, or poly-N-substituted glycines, are a class of peptidomimetics whose side chains are appended to the nitrogen atom of the peptide backbone, rather than to the α-carbons (as they are in amino acids).
In peptoids the side chain is connected to the nitrogen of the peptide backbone, instead of the α-carbon as in peptides. Notably, peptoids lack the amide hydrogen which is responsible for many of the secondary structure elements in peptides and proteins. Peptoids were first invented by Reyna J. Simon, Paul Bartlett and Daniel V. Santi to mimic protein/peptide products to aid in the discovery of protease-stable small molecule drugs.
Following the sub-monomer protocol originally created by Ron Zuckermann, each residue is installed in two steps: acylation and displacement. In the acylation step a haloacetic acid, typically bromoacetic acid activated by diisopropylcarbodiimide reacts with the amine of the previous residue. In the displacement step (a classical SN2 reaction), an amine displaces the halide to form the N-substituted glycine residue. The submonomer approach allows the use of any commercially available or synthetically accessible amine with great potential for combinatorial chemistry.
Like D-Peptides and β peptides, peptoids are completely resistant to proteolysis, and are therefore advantageous for therapeutic applications where proteolysis is a major issue. Since secondary structure in peptoids does not involve hydrogen bonding, it is not typically denatured by solvent, temperature, or chemical denaturants such as urea (see details below).
Notably, since the amino portion of the amino acid results from the use of any amine, thousands of commercially available amines can be used to generate unprecedented chemical diversity at each position at costs far lower than would be required for similar peptides or peptidomimetics. To date, at least 230 different amines have been used as side chains in peptoids.
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