In simple terms, Peptide synthesis is the formation of peptide bond between two amino acids; where, a peptide refers to flexible chains of 30-50 amino acids. Peptide synthesis process has been around since over 100 years; however, synthesis including ‘Oxytocin’ and ‘Insulin’ came later. Over the years, the efficiency of synthesis chemistry improved rapidly and today, it has become a common approach in biological research centres. It is more commonly used of peptide in cosmetic products and drug development.
Its primary advantage is that, essential peptides found in biological specimens can now be made in a lab. Moreover, they can be optimized to produce desired biological responses by adding additional attributes to original peptides. It is often done by coupling carboxyl group of amino acid to the N-terminus of peptide chain (C-to-N synthesis). However, due to its complex nature, the coupling is controlled in strict steps of cyclic processes.
Amino acids are added to the growing peptide chain, one at a time. They have numerous reactive groups; hence, must be carefully performed to avoid any side reaction, such as reduction of length and branching of peptide chain. Therefore, research centres have developed chemical groups that bind to the specific reactive blocks of amino acid and protect the functional group.
Individual amino acids are reacted with the protecting groups before synthesis Some protecting groups are removed from the added amino acid after coupling. This step is called a ‘Deprotection’. It facilitates new incoming amino acids to bind to the peptide chain. After completion, remaining protecting groups are removed from peptides
Commonly used protecting groups:
N-terminal protecting groups:
- They are relatively easy to remove in order to allow peptide bond formation; e.g. tert-butoxycarbonyl (Boc) and 9-fluorenylmethoxycarbonyl (Fmoc)
- ‘Boc’ requires a strong acid such as trifluoracetic acid (TFA) to be removed from the newly added amino acid. They need acidic conditions for deprotection
- Whereas ‘Fmo’c is a base-labile protecting group and can be removed with a base – piperidine. They are commonly used in commercial products
C-terminal protecting group:
- Liquid-phase synthesis requires protection of the C-terminus
- Solid-phase synthesis does not require protection because the solid support acts as the protecting group.
Amino acid side chains:
They are known as permanent protecting groups, because they can withstand multiple cycles of chemical treatment during the synthesis phase and are only removed after synthesis is complete.
Applications of synthetic peptides:
Invention of peptide synthesis encouraged Custom peptide synthesis services to development of numerous application areas such as:
- Development of epitope specific antibodies, specifically used against pathogenic proteins
- Study of protein functions i.e. to identify and characterize
- Study of enzyme-substrate interactions in enzyme classes such as kinases and proteases. It is crucial in cell signalling.
- They can resemble natural peptides; hence can be used as a part of treatment against major diseases.
- They can be used as reagents in mass spectrometry based applications