Peptides laboratory synthesis

Synthesis. In contrast to pituitary hormones, which usually can be obtained in pure form only after extraction from animal tissues, brain oligopeptides are readily available because of their small size. The synthetic repHca represents the most economical and readily accessible source for the oligopeptides. Two techniques are available for laboratory synthesis of oligopeptides, ie, solution chemistry and soHd-phase peptide synthesis (SPPS). 

Ethers with a tertiary, benzylic, or allylic group cleave by an S l or FI mechanism because these substrates can produce stable intermediate carbocations. These reactions are often fast and take place at moderate temperatures. fcrf-Butyl ethers, for example, react by an El mechanism on treatment with trifluoroacetic acid at 0 °C. We ll see in Section 26.7 that the reaction is often used in the laboratory synthesis of peptides. 

We ll see in Section 26.7 that this DCC-induced method of amide formation is the key step in the laboratory synthesis of small proteins, or peptides. For instance, when one amino acid with its NH2 rendered unreactive and a second... 

The problems involved in peptide syntheses are of much practical importance and have received considerable attention. The major difficulty in putting together a chain of say 100 amino acids in a particular order is one of overall yield. At least 100 separate synthetic steps would be required and, if the yield in each step were equal to n x 100%, the overall yield would be (n1U0 x 100%). If the yield in each step were 90%, the overall yield would be only 0.003%. Obviously, a practical laboratory synthesis of a peptide chain must be a highly efficient process. The extraordinary ability of living cells to achieve syntheses of this nature, not of just one but of a wide variety of such substances, is truly impressive. 

Understand the laboratory synthesis of a peptide in solution or by the solid phase method. (Problems 26.35 and 26.36)... 

Amino Adds, Peptides, and Proteins 26.7 Laboratory Synthesis of Peptides Active Figure 26.4 Mechanism of Amide Formation Using Dicydohexylcarbodiimide (page 1151) Coached Tutorial Problem Reactions Used in Synthesis of Peptides (page 1151)... 

Among many other peptide splitting enzymes such as (bacterial) subtilisin and thermolysin, (vegetable) papain, ficin and bromelain, (mammalian) cathepsin and others, the yeast enzyme carboxypeptidase Y finally deserves special mention. The enzyme is an exopeptidase, like carboxypeptidase A i.e. it catalyzes, rather unspecifically, the hydrolytic fission of the carboxy-terminal a-amino acids from a peptide chain. J.T. Johansen and his associates at the Carlsberg laboratory in Copenhagen showed about 10 years ago that CPD-Y is an effective catalyst of peptide bond synthesis [36]. 

Winnick and coworkers had described a system using cell-free extracts of Bacillus hrevis for the synthesis of gramicidin and tyrocidine. The s5mthesis appeared to be similar to that usually found for protein synthesis. It was inhibited by puromycin and chloramphenicol and was RNAase sensitive. As the galley proof for this review was being examined, a paper entitled The Biosynthesis of Gramicidin S. A Restudy was published by Winnick s laboratory (Bhagavan, Rao, Pollard, Rao, Winnick and Hall, 1966). It was reported that they were unable to repeat the previous experiments which had indicated that a ribosomal system was involved in peptide antibiotic synthesis and, consequently, a reassessment of the earlier reports was made. 

With slant cultures of an Elymus-type Claviceps strain, Ohashi and Abe (1970) obtained cell-free conversion of agroclavine and elymoclavine to peptide alkaloids. There have been no reports so far of cell-free peptide alkaloid synthesis with shake cultures. Groger s laboratory (Maier et al., 1972) studied the activation reactions that could be involved in peptide alkaloid biosynthesis. They observed cell-free synthesis of lysergyl-CoA and activation of valine, serine, leucine, and proline. Activation was found in nonproducing, clavine alkaloid-producing, and peptide alkaloid-producing strains. The connection between these activities and peptide alkaloid synthesis is therefore uncertain. 

---