Peptides play a significant and expanding role in drug discovery, and are a consistent source of inspiration due to their unique properties and diverse applications in the development of novel therapeutics. Highlighted below are some examples that illustrate the practical application of peptides.
- Biological Revelance: Peptides are essential components of many biological processes in the human body, and they often serve as signaling molecules, enzymes, and receptors.
- High Target Specificity: Peptides can be highly specific in their interactions with target proteins, which can be advantageous for therapeutic applications. This specificity can potentially reduce off-target effects, making peptides ideal for targeting specific disease mechanisms.
- Peptide-Based Vaccines: Peptides are used in the development of vaccines, particularly in cancer immunotherapy. Peptide-based vaccines can stimulate the immune system to recognize and target specific antigens associated with diseases like cancer.
- Drug Conjugates: Peptides can be used as components of drug conjugates, where they serve as targeting agents. This approach is particularly useful in targeted cancer therapy, where the peptide guides the drug to cancer cells while sparing healthy tissues.
However, peptides come with some limitations regarding their physicochemical properties. At Symeres, our experienced scientists are well equipped to overcome these drawbacks by synthesizing peptidomimetics. These compounds are designed to eliminate a peptide’s weak spots, while maintaining the structural features responsible for its biological activity.[1],[2] Two major classes of peptidomimetics that our chemists frequently work with are described below.
Amide isosteres
The amide functionality forms the backbone of peptides and is also often found in other early drug compounds. However, amide-rich compounds often show poor pharmacokinetic properties with respect to metabolic stability and permeability, making amide replacement desirable. At Symeres, we tackle this by applying the concept of bioisosteric replacements. These bioisosteres mimic the many specific properties of an amide group, e.g., size, rigidity, polarity, and H-bond acceptor/donor, but possess more favorable properties when it comes to, e.g., hydrolytic stability. For example, 1,4-disubstituted 1,2,3,-triazole can be used to replace a trans-amide bond, whereas 1,5-disubstituted 1,2,3,-triazoles are used to replace a cis-amide bond. Some more examples from our toolbox of amide isosteres can be found in the figure below[3].
Peptide cyclization
Macrocyclization of linear peptides is shown to be another effective way to overcome the shortcomings of peptide-based drug leads[1],[4]. For example, compounds aimed at targeting protein–protein interactions can benefit from decreased flexibility. Moreover, cyclization often also leads to improved proteolytic stability. In addition to the classical head-to-tail amide formation (lactamization), peptides can also be cyclized in side-chain-to-tail, head-to-side-chain, or side-chain-to-side-chain formations. Within Symeres, we have extensive experience in preparing such cyclic peptidomimetics via, e.g., copper-catalyzed azide–alkyne cycloaddition (CuAAC), ring-closing metathesis (RCM), disulfide formation, thioether formation, disulfide stapling, and classical lactamization. Furthermore, our toolbox for preparing non-proteinogenic amino acids allows us to prepare tailor-made peptide building blocks for the various cyclizations.
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[1] E. Lenci et al., Chem. Soc. Rev. 2020, 49 , 3262 DOI: https://doi.org/10.1039/D0CS00102C
[2] N.A. Meanwell, Top. Med. Chem 2015, 99 , 283–382 DOI: https://doi.org/10.1007%2F7355_2013_29
[3] S. Kumari et al., J. Med. Chem. 2020, 63 , 283–382 DOI: https://doi.org/10.1021/acs.jmedchem.0c00530
[4] R.M.J. Liskamp et al., ChemBioChem. 2011, 12 , 1626–1653 DOI: https://doi.org/10.1002/cbic.201000717
