Solid phase peptide synthesis is one of the most important breakthroughs in the field of peptide synthesis. The method was developed by R B Merrifield, and it basically makes it possible for peptides and small proteins to be synthesized chemically. The first step of the SPPS technique, features the assembly of the peptide chain using protected amino acid derivatives. The next step is the cleavage of the peptide with the accompanying cleavage of all the side chains, offering protection to the groups to result into crude free peptide.
The basic principle of solid phase peptide synthesis features repeated cycles of what is scientifically termed as coupling-deprotection. The single N-protected amino acid is coupled to the free N terminal of the amine. The unit is then de-protected to reveal a new N terminal amine where another amino acid may get attached.
Solid phase peptide synthesis has two major methods applicable at the moment – these include t-Boc and Fmoc methods. Each of the methods feature different amino acid side chain protection, and resins, and this leads to different de-protection and cleavage steps. Fmoc is known to produce peptides of higher quality and better yield than t-Boc. With t-Boc, a lot of impurities normally arise, and this is attributed to t-butylation, dehydration, and issues to do with the cleavage.
The purification of peptides is normally done using reverse phase HPLC once the cleavage of the resin is complete. The main benefit of using solid phase peptide synthesis, is the amount of yield realized. Since peptides contain a lot of amino acids, the overall yields, however, may be negligible if the yield of each addition of amino acid is less than 100%. It is also important to observe that through the use of modern instrumentation and technology, deprotection and coupling yields are relatively higher with SPPS, and it is possible to realize yields of more than 99% from a 50 amino acid peptide.