Overview of Peptoids and Peptoid Libraries

• The Promise of Peptides as Drug Candidates
• Advantages of Peptoids vs. Peptides
• Peptoid Synthesis
• Generation of Peptoid Libraries
• Affinity Enhancement of Peptoid Ligands and Drug Candidates
• Custom Peptoid Assay Development

For nearly 20 years, peptides have been considered a promising class of drugs that possess distinct advantages over small molecule and biologic drugs. Compared to small molecule drugs, peptides can exhibit better efficacy, higher specificity, and lower toxicity. Compared to protein-based biologic pharmaceuticals, peptides are relatively inexpensive to produce and can easily be synthesized to exacting standards of purity and reproducibility between batches. Moreover, their chemistry and small size allows peptides to assume conformations that can mimic portions of full-length proteins or small molecules.

In practice, most peptide drug candidates have not lived up to the promise. Their susceptiblity to proteolytic cleavage, relatively short half-life in the body, and low oral and tissue bioavailability, make peptides less-than-ideal drug candidates. These challenges have hampered the translation of peptide drug candidates into therapeutics.

To overcome these inherent drawbacks, some researchers have investigated the potential for using peptide mimetics instead.  Some of the most promising peptidomimetic compounds are peptoids.

Peptoids are polymers of N-substituted amino acids that mimic many of the properties of peptides, but with distinct advantages. Peptoids have longer half-lives due to their  resistance to proteolysis; they also permeate cell membranes much better than peptides, resulting in greater bioavailability. Peptoids also have a much greater conformational freedom compared to a peptide of similar length, allowing a greater number of possible conformations, which can enhance sensitivity.

Like peptides, peptoids can be synthesized using commercially available amines.  Polystyrene beads with primary amine groups on their surface react with chloroacetic acid in the presence of N,N'-diisopropylcarbodiimide (DIC) to produce a chloromethyl intermediate. Peptoid monomers (primary amines) can then acylate the chloromethyl group by nucleophilic SN2 displacement. As with peptides, synthesis is step-wise, adding only one residue in the peptoid chain in each round of acylation. Additional peptoid residues can then be added to the chain in subsequent rounds using these same reactions.

Raybiotech can synthesize single peptoids using our stock of primary amines or specific amines specified by the customer. The purity of the peptoid ranges from 85% to 95%; mass spectrometry data will be provided.

Peptoid libraries can be created by the conventional split-and-pool method on polystyrene beads. Depending on the number of different primary amine monomers and the number of residues used, combinatorial synthesis can generate oligopeptoid population diversities of 10⁵ to 10¹⁰ or even greater.
Let RayBiotech build a custom combinatorial peptoid library for screening against your protein of interest. You specify the primary amines and library diversity.

Screening of peptoid libraries can help identify high-affinity ligands for the protein or other molecules of interest. Beads with the combinatorial peptoid library are placed in ELISA plate wells and incubated with cell lysates, which serves to block non-specific binding, followed by incubation with the molecule of interest.  Then an antibody specific for  the molecule of interest is used to tag the bound target protein, and a secondary (anti-Fc) antibody labeled with a fluorescent tag provides the signals for detection. Bead slurries are then examined under a microscope. Beads with significant affinity, as indicated by a strong fluorescent signal, can then be isolated and the sequence of peptoids on each bead is determined by Edman degradation.

RayBiotech will screen, identify, and sequence specific peptoid ligands to your target protein. We can use our in-house peptoid library or your own custom library.

After high-affinity candidates are identified by screening, the affinity can be further enhanced. Once the sequences of candidate peptoids are determined, a second combinatorial peptoid library is constructed by introducing a specific monomer amine at each residue position in the peptoid chain.  A second round of screening is then performed on the permutated library to identify peptoids with even higher affinity for the target.

For certain target proteins, we can develop a cell-based secondary assay to validate the activity of your peptoid ligand. Contact a technical support representative for more details.

 Back to Peptoid Services.