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Merrifield solid phase peptide synthesis
From the last 40 years or so Merrifield solid peptide synthesis has been a standard research procedure used in further study of chemistry and biological usage of deamidation of asparanginyl and glutaminyl residues in peptides. In its primary investigation, initially, it permitted the qualitative demonstration in three different structure-determining deamidation which varied over a wide range in different biological conditions and the discovery of two biological systems took place in which deamidations works as molecular clocks. In the recent times a thorough quantitative understanding of the structural dependence of deamidation became possible which results in deamidation rate of asparanginyl residues in protein can be predicted from three dimensional structure of protein with a high degree of accuracy. In his investigation, Professor R.B. Merrifield discovered that amide residues serve as molecular clock in many biological systems. It is this technique on which Merrifield solid phase peptide synthesis is based and named. Merrifield contributed his technique, time, and resources, both in teaching his methods to principle investigators and in providing his laboratory where more than 900 peptides were synthesized for his work. A protein contains one peptide folded in a specific way, or several peptides folded together. Such peptides are generally synthesized very quickly within living cells, but artificially the synthesis takes longer time because the artificial process is slow resulting poor yields and impure products. However, what Merrifield developed, the Merrifield solid phase peptide synthesis (SPPS), was a major breakthrough in artificial protein production through peptide synthesis. SPPS results in high yields of pure product and works quickly than classical form of synthesis (liquid phase peptide synthesis, LPPS). The benefits of SPPS methods are very considerable. A lot of times is saved in replacement of a complicated isolation procedure for each intermediary product with a simple washing procedure. Furthermore, it has proven that it is possible to increase yield in each individual steps to 99.5% or better, a result which cannot be attained using conventional method of synthesis. The SPPS method discovered by Merrifield brought in a kind of revolution in peptide and protein chemistry and thousands of different peptides have been synthesized using this method. In methodology, this is completely a new approach to organic synthesis. It has created new possibilities in the field of research and study of peptide-protein chemistry and nucleic acid chemistry. It has also stimulated progress in biochemistry, molecular biology, pharmacology and medicine. It is also of great practical importance, both for the development and discovery of new drugs and gene technology.
The synthesis of peptides and small proteins in which the resinous polymer supports amino acid and succeeding peptide repeatedly reacts with N-protected amino acids followed by deprotection until the desired peptide or protein is accumulated is generally referred to as the Merrifield solid phase peptide synthesis and the polymeric resin is known as the Merrifield resin. The starting protocol using N-benzyloxycarbonyl-protected amino acid has been worked upon to improve and developed into two corresponding methods. In the first method the N-t-butyloxycarbonyl (Boc) protected amino acid is linked to the solid phase via a linker moiety and the second protocol uses 9-fluorenylmethyloxycarbonyl (Fmoc) as the amino protecting group, which can be easily sliced. It has also been found that the ongoing peptide chain could stop growing or end up to a low yield of peptide, due to the association of the peptide chain, the swelling problem of the resin, etc. The study finds that application of a mixed solvent of CH2Cl2 and DMF apparently enhances the result. This reaction has been applied for the preparation of peptides and small proteins.
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