Polypeptides chemical synthesis

It is notable that small peptides were retained on a cross-linked PEI column [37] but polypeptides over 20 residues were weakly retained or not at all. Possibly, small peptides were able to penetrate into the depth of the bonded phase while larger peptides could not. These packings were more useful for the separation of oligonucleotides, i.e. more acidic compounds. Lawson et al. [39] have shown the applicability of PEI-silicas for assessing the purity of precursor blocks, monitoring the chemical synthesis and isolating reaction products after synthesis. 

ELPs can be produced via chemical synthesis and biosynthetically. For chemical synthesis via solid phase peptide synthesis, the attainable polymer length is limited, and if long polymers with a defined length are required then the biosynthetic approach is more appropriate. An advantage of chemical synthesis is, however, that it enables the facile introduction of functional residues in the polypeptide [27]. 

An alternative approach to the production of subunit vaccines entails their direct chemical synthesis. Peptides identical in sequence to short stretches of pathogen-derived polypeptide antigens can be easily and economically synthesized. The feasibility of this approach was first verified in the 1960s, when a hexapeptide purified from the enzymatic digest of tobacco mosaic virus was found to confer limited immunological protection against subsequent administration of the intact virus. (The hexapeptide hapten was initially coupled to bovine serum albumin, used as a carrier to ensure an immunological response.)... 

It has long been known that peptides of bacterial origin, such as N-formylat-ed oligopeptides, are potent activators of neutrophils. Bacterial protein biosynthesis is initiated by the codon AUG, which codes for polypeptide chains at the NH2 terminus to start with N-formylmethionine. However, very few mature bacterial proteins actually have this amino acid at the NH2 terminus because Af-formylmethionine is cleaved off by proteolytic processing. Sometimes just this amino acid is cleaved, but often several adjacent residues are also removed with it. These observations formed the basis for the chemical synthesis of a variety of N-formylated oligopeptides and an assessment of their ability to activate neutrophils in vitro. The most potent of these formylated peptides is TV-formylmethionyl-leucyl-phenylalanine (fMet-Leu-Phe). 

Smith, J.C., Derbyshire, R.B., Cook, E., Viney, J., Brewer, S.J., Sassenfeld, H.M. and Bell, L.D. (1984) Chemical synthesis and cloning of a poly-arg gene fragment designed to aid polypeptide purification. Gene, 32. 321-327. 

Methods of chemical synthesis of polypeptides and of cloning and mutating genes now allow us to alter peptide sequences at will and to design completely new proteins 355-356b The methods are discussed in Chapters 3, 5, and 26. The following are examples. 

Polypeptide(s) 56 - 59. See also Proteins antibiotics 66 chemical synthesis 85 conformation of 59 - 61, 78 definition of 51 torsion angles 59-62 Polypeptides. See also Peptides Polyphosphates 302, 303 Polyprenyl compounds... 

Determination of Amino Acid Composition of Proteins Determination of Amino Acid Sequence of Proteins Chemical Synthesis of Peptides and Polypeptides... 

Chemical synthesis has provided an additional route to peptides containing halogenat-ed amino acids. Early 19F-NMR studies of proteins were performed on semi-synthetic polypeptides prepared by attachment of fluorinated probes to the polypeptide. For example, Heustis and Raftery modified ribonuclease by trifluoroacetylation of Lys residues 1 and 7. They then used 19F-NMR to study conformational changes brought about by the presence of inhibitors200. In his review, Gerig provides several other examples of this strategy187. 

Amino acids are monomeric units of polypeptides and proteins. They are widely used in the food and chemical industries as flavor enhancers, seasonings and sweeteners e.g. for the improvement of bread quality, also in the production of drugs, cosmetics, synthetic leather and surfactants, in medicine for infusions and as therapeutic agents. Amino acids are produced by chemical synthesis or extraction from protein hydrolyzate. They may be also produced by microbiological methods. 

Another method to introduce unnatural amino acids into a polypeptide chain is through complete chemical synthesis (10). The predominantly used method, stepwise solid-phase peptide synthesis (SPPS), attaches the C-terminal amino acid to a solid support, and amino acids are added one at a time to the N-terminus. A clear advantage of chemical synthesis is that it enables the accurate introduction of unnatural amino acids at any site in a protein. The number of unnatural amino acids that can be introduced is limited only to the size of the chain, and chains of entirely unnatural amino acids can be produced using this method. Chemical synthesis is useful particularly for the incorporation of isotopic labels and unnatural amino acids that are toxic to cells or incompatible with the translational machinery. However, construction of a polypeptide chain using even the most advanced chemical synthesis techniques is daunting when confronted with the construction of an entire protein, as these methods currently are limited to approximately 100 amino acids (10). 

How to synthesize biologically active polypeptides chemically has long been an important challenge for many fields in chemistry and biology. In the past, the development of solution-phase and solid-phase synthesis techniques has made it possible to synthesize large molecules like peptides with molecular weights up to 10,000. The purpose of this review is to provide an overview of how to prepare natural bioactive peptides synthetically. Because of space limitations, this review concentrates on peptide hormones and neurotransmitters. 

The chemical ligation strategy has been applied primarily to the formation of bonds involving cysteine and homocysteine the latter residue can be converted into methionine by methylation. Moreover, the number of examples of this approach is rather limited and side reactions have been noted which will probably be unique for individual polypeptides. Nevertheless, this strategy would appear to have great potential in the chemical synthesis of long polypeptides. Section 4.1.5 extensively discusses the chemical ligation field. 

In view of these possible complications, the chemical synthesis of peptides is generally performed in the C-to-N direction by a stepwise elongation approach using preferentially A -alkoxycarbonyl-protected amino acid derivatives to produce the target polypeptide chain in solution and on solid supports directly. Specially designed intermediate segments, usually... 

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