Chemical synthesis of peptides and proteins

For the synthesis of most dipeptides, protection of amino-acid residue side-chain functional groups will also be appropriate in order to avoid additional undesirable side reactions. 

Furthermore, coupling (peptide link formation) need to be performed under very carefully controlled conditions, otherwise a-carbon racemisation becomes a serious problem, especially during coupling. This is so because, each selected N-terminal protected amino acid 

Problems in solution phase peptide synthesis have been largely overcome by the development of solid phase peptide synthesis (SPPS). The chemical principles of peptide link formation and peptide synthesis remain the same, but in SPPS the growing peptide chain is anchored to a solid phase resin, thereby easing the iterative process of peptide bond formation, removing the need for crystallisations and purifications after each step of the synthesis, and in some ways simplifying protection/deprotection problems. SPPS earned Bruce Merrifield a Nobel Prize in 1986, and has eased the technical challenges of peptide synthesis to the extent that the process can now be automated. 

The solid support should be well solvated to facilitate reactions to take place involving the two phases. The original supports were based on polystyrene but have generally been superseded by polyamide resins, which have an advantage in that they have a similar polarity to the peptide backbone. More recently, resins based on polyethylene glycol (PEG) grafted onto low 

These are all acid labile (see illustrated mechanism). Most common solid phase resins are also shown, all of which are labile to acidic release conditions too (the rink amide leaves a C-terminal amide in place). During global deprotection and resin removal, scavengers such as phenol, cresol or thioanisole are also included to capture reactive cationic species post deprotection. The desired product oligo-/p°lypeptide is then separated initially by precipitation by means of an agent such as methoxy-tert-butyl ether (MTBE) and purified finally by reversed phase liquid chromatography (see later in Chapter 2). 

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A number of reactions of amino acids have become important in recent years because they are essential to the degradation, sequencing, and chemical synthesis of peptides and proteins. These reactions are discussed in Chapter 5. 

R. B. Merrifield, Methods. Enzymol. 289 3 (1997) K. B. Merrifield, in Peptides Synthesis, Structure, and Applications, B. Gutte, ed., Academic Press, San Diego, 1995, p. 93 Atherton and R. C. Sheppard, Solid Phase Peptide Synthesis, IRL Press, Oxford, U.K., 1989 P. Lloyd-Williams, F. Albericio, and E. Giralt, Chemical Synthesis of Peptides and Proteins, CRC Press, Boca Raton, Florida, 1997. 

This expresses the feelings of others in this field, and even today most syntheses have been undertaken mainly to examine the new methodology at hand and to test its limits. The second objective then becomes the application of the technology to answer important chemical and biological questions through the chemical synthesis of peptides and proteins. 

S. B. H. Kent, Chemical synthesis of peptides and proteins, Annu. Rev. Biochem. 547 957... 

Although chemical synthesis of peptides and proteins has developed substantially in recent decades, it does require use of toxic reagents, large amounts of expensive reagents, and often suffers from incomplete reactions that significantly reduce final product purity. Chemical synthesis can be performed in solution, on a solid phase, or by a combination of both. Solution-phase synthesis has been the method of choice for large-scale preparation, but developments in solid phase tools have enabled its use also. 

Chemical Synthesis of Peptide- and Protein-Polymer Conjugates... 

I. Galpin, Chemical Synthesis of Peptides and Proteins , Chem. in Britain, 1978, 14,181. 

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