A condensation reaction forms 2-50 amino acids that join together through a covalent bond to create a peptide. A sequence of covalent bonds with numerous amino acids creates a peptide chain which serves as protein’s building blocks. Peptide synthesis takes place when two amino acids form a peptide bond.
Peptide synthesis is a polymer formed by linking amino acid subunits. Chemical peptide synthesis is usually a challenging task. Oxytocin and insulin were among the first peptides to be synthesized, and it took 50-60 years to occur. However, there have been great strides and advances in protein synthesis chemistry in the last fifty years. That has made it a shared approach today in drug development and biological research. The reduction of the difficulty to conduct peptide synthesis has opened the way for more imaginative and innovative peptide synthesis. This article takes you through the five processes for synthesizing peptides.
Processes of Peptide Synthesis
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Peptide Deprotection
In the deprotection of peptides, chemical groups that bind to the reactive groups and block protect functional groups from nonspecific reactions. That will facilitate the formation of peptides with as many minimal side reactions as possible. Peptide synthesis usually is prone to side reactions because amino acids contain multiple reactive groups. It is essential to minimize side reactions to reduce the cause and length of branching of the peptide chain.
Amino Acid Coupling
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The C-terminal carboxylic acid is activated on an incoming amino acid through carbodiimides like diisopropyl carbodiimide (DIC) or dicyclohexylcarbodiimide (DCC). The carbodiimides or coupling reagents form a reaction with the carboxyl group. Subsequently, it forms a highly reactive O-acylisourea intermediate. Nucleophilic attack from the deprotected primary amino group displaces the O-acylisourea forming the nascent peptide bond.
The racemization of the amino acid is triggered by the carbodiimides forming the reactive intermediate mentioned above. So, reagents like 1-hydroxy benzotriazole (HOBt) are often added to react with the O-acylisourea intermediate and reduce the risk of racemization.
Peptide Cleavage
After successfully undertaking the coupling and acid protection cycles, the remaining protecting groups are removed from the nascent peptide. At this stage, the remaining protecting groups are cleaved using acidolysis. The protection schemes used will determine the chemicals used for cleavage. With proper execution of the cleavage, the results will be such that the N-terminal protecting group of the last amino acid added is removed. Additionally, scavengers are included to react with free protecting groups. At this step, you should use optimization to avoid acid-catalyzed side reactions.
Liquid-Phase Peptide Synthesis
Liquid-phase peptide synthesis is a classical method scientists use to discover how to generate peptides in vitro. It is still used commonly for large-scale synthesis. Since one has to manually remove the product from the reaction solution in every step, this method becomes quite labor-intensive and slow. Another chemical group is needed to protect the first amino acid’s C-terminus in this approach.
The advantage of this strategy is that it allows for purification in every step, thus making it easier for easy detection of side effects. Another strategy is a convergent synthesis that involves synthesizing peptides that are then coupled together to create larger peptides.
Peptide Purification
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The process of peptide generation is by no means perfect, even with the optimization of its strategies. Events like incomplete deprotection or reaction with free protecting groups could lead to deletion sequences, isomers, and other products. Because of that, purification strategies have been applied.
They are based on separation methods that exploit peptides’ physicochemical characteristics. Such characteristics include hydrophobicity, size, and charge. Some of the purification techniques include; Partition chromatography, size-exclusion chromatography, ion-exchange chromatography, and high-performance liquid chromatography (HPLC).
Clinical Significance
Peptides are very significant in many psychological processes in the body. They serve a critical role in clinical significance, as demonstrated below.
Chronic Inflammatory Skin Conditions
Healthy skin defends against surface attacks by secreting AMPs. The attacks could be from gram-negative viruses, bacteria, or fungi. In this case, peptides play a huge role in offering defence to the skin. It has been found that peptides play a role in predisposing the skin to pathogenic infections. A chronically disrupted epithelial microbiome predisposes the tissue to persistent inflammatory skin conditions and pathogenic infections.
Wound Repair
Endogenous peptides have contributed significantly to the healing of wounds. They also induce mesenchymal cells to promote and differentiate bacteriolysis within the wound while facilitating healing. Syndecan activates the growth factors of heparin-binding and tissue matrix substances which facilitates the repair of damaged tissues and wound repair.
Tumor Targeting and Molecular Imaging
Peptides act as receptor binding peptides and imaging probes for the overexpressed receptors like cancer proliferation through specific receptor binding and endogenous peptides. Vitro strategically designs the probes to mimic endogenous peptides acting as biomarkers and allowing the detection of tumors. Therefore, this advanced technology plays a massive role in identifying tumor growth and therapeutic processes.
Final Thoughts
Peptide synthesis continues to mark significant advances as biochemical sciences and therapeutic design progress. The area is heavily studied alongside its implications for oncologic therapy even as the pharmaceutical industry continues shifting more towards biologicals to create new drug candidates.