Merrifield synthesis of peptide

Figure 9.1.1 Combinatorial peptide libraries as obtained by Merrifield synthesis of peptides on membrane-covered gold particles allow not only investigations of recognition processes between the surface receptors and water-soluble substrates. Systematic changes of the environment of the receptor also become feasible (see Secs. 9.3.2 and 9.6.10). Steps I, III, and V are coupling reactions steps II, IV, and VI are deprotection reactions. About 50 thiolate molecules, including dodecyl sulfide and three peptides, have been deposited on a single gold cluster in statistical distributions and arrangements. (From Templeton et al., 1998.)...

In addition to ion exchange resins, polymer reagents also include what are called redox or oxidation-reduction polymers which also represent electron transfer agents. Polymer reagents are also used in the Merrifield synthesis of peptides and proteins (see Chapter 30). Other polymer reagents, together with their applications, are... 

R. B. Merrifield (Rockefeller, New York) development of methodology for the synthesis of peptides on a solid matrix. 

Robert Bruce Merrifield (1921-2006) was born in Fori Worth, Texas, anti received his Ph.D. at the University oi California, Los Angeles, in 1949. He then joined the faculty at the Rockefeller Institute, where he remained until his death. In 1984, he was awarded the Nobel Prize in chemistry for his development of methods for the automated synthesis of peptides. 

One of the key technologies used in combinatorial chemistry is solid-phase organic synthesis (SPOS) [2], originally developed by Merrifield in 1963 for the synthesis of peptides [3]. In SPOS, a molecule (scaffold) is attached to a solid support, for example a polymer resin (Fig. 7.1). In general, resins are insoluble base polymers with a linker molecule attached. Often, spacers are included to reduce steric hindrance by the bulk of the resin. Linkers, on the other hand, are functional moieties, which allow the attachment and cleavage of scaffolds under controlled conditions. Subsequent chemistry is then carried out on the molecule attached to the support until, at the end of the often multistep synthesis, the desired molecule is released from the support. 

RB Merrifield, JM Stewart, N Jemberg. Instrument for automated synthesis of peptides. Anal Chem 38, 1905, 1966. 

MERRIFIELD RESIN FOR SYNTHESIS OF PEPTIDES USING BOC/BZL CHEMISTRY... 

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. 

Formation of an amide bond (peptide bond) will take place if an amine and not an alcohol attacks the acyl enzyme. If an amino acid (acid protected) is used, reactions can be continued to form oligo peptides. If an ester is used the process will be a kinetically controlled aminolysis. If an amino acid (amino protected) is used it will be reversed hydrolysis and if it is a protected amide or peptide it will be transpeptidation. Both of the latter methods are thermodynamically controlled. However, synthesis of peptides using biocatalytic methods (esterase, lipase or protease) is only of limited importance for two reasons. Synthesis by either of the above mentioned biocatalytic methods will take place in low water media and low solubility of peptides with more than 2-3 amino acids limits their value. Secondly, there are well developed non-biocatalytic methods for peptide synthesis. For small quantities the automated Merrifield method works well. 

R. Bruce Merrifield Chemistry Solid-phase synthesis of peptides... 

One of the major tools in combinatorial chemistry has been rooted in the ingenious solid-phase synthesis of peptides by Merrifield.1... 

The synthesis of peptides on a solid support, usually beads of either polystyrene (the Merrifield approach) or polyamide (the Sheppard approach) resins has become extremely important, because it allows peptides to be synthesized by machines, and a key feature of the Sheppard approach is the use of Fmoc-protected amino acid residues. The idea is that the C-terminus amino acid is tethered to the resin by means of a carbamate linker that is stable to mild acid or base. The peptide chain is then built up using the sorts of methods we have been discussing and, when complete, is released by cleaving the linker with strong acid. 

Now some detail—and we will discuss the Merrifield version of peptide synthesis. Spherical cross-linked polystyrene beads of about 50 pm in diameter are used and attached to various spacers of which the simplest is just a CH2 group from the chloromethylated polystyrene we have just discussed. The caesium (Cs) salt of the amino acid is used to displace the chloride as it is a better nucleophile than the Na or K salts. A better alternative is Pam (shown in the margin). It can be used as the nucleophile to displace the chloride first. The amino acid is then added after purification. No chloromethyl groups can remain on the polymer with this spacer. 

Merrifield s idea of the synthesis of peptides on solid support (5-9) fundamentally changed the thinking of peptide chemists (even though, depending on the personality of the scientists, the adoption of the solid phase methodology sometimes required a very long induction period ). Later, as it became... 

There are two general approaches to the synthesis of peptides the classical method, in which all reactions are carried out in homogeneous solution, and the solid phase method, in which the reactions are heterogeneous ones between soluble reagents and an insoluble peptide chain that is attached to a solid support. Since its introduction by Merrifield in 1962 solid-phase peptide synthesis has been applied successfully to the preparation of a great number and variety of peptides including proteins [1,2]. 

The recommended procedure for the synthesis of peptide amides is to use a resin (e.g., MBHA) that yields amides directly upon cleavage with HE Ammonolysis can be used to give amides of peptides on Merrifield or HMBA resins. Anunonolysis can also probably be used with PAM resins. 

The principal difference between the synthesis of individual peptides and peptide libraries is that mixtures of amino acids, rather than individual amino acids, are incorporated into selected or all positions of the sequence of peptide libraries. However, all current peptide chemistry strategies can be used for the synthesis of peptide libraries. In general, library synthesis requires greater emphasis on simplicity and reproducibility of the synthesis process. Although soluble supports have also been used for peptide library synthesis,the majority of methods used to synthesize peptide combinatorial libraries utilize Merrifield s concept of solid-phase synthesis,which is based on the sequential assembly of peptides after covalent attachment of the C-terminal amino acid to a polymeric solid support. This enables the excess of reagents to be removed by simple wash and filtration processes, and avoids the... 

Although the solid-phase technique was first developed for the synthesis of peptide chains and has seen considerable use for this prupose, it has also been used to synthesize chains of polysaccharides and polynucleotides in the latter case, solid-phase synthesis has almost completely replaced synthesis in solution. The technique has been applied less often to reactions in which only two molecules are brought together (nonrepetitive syntheses), but many examples have been reported. Combinatorial chemistry had its beginning with the Merrifield synthesis, particularly when applied to peptide synthesis, and continues as an important part of modem organic chemistry. ... 

Solid-phase synthesis of peptides was pioneered by Bruce Merrifield in the early 1960s. This work, for which he won the Nobel Prize in 1984, set in motion the modern approach to drug discovery called combinatorial chemistry. Through combinatorial chemistry, millions of compounds are generated by the synthesis of libraries on solid supports and screened for therapeutic activity by high-throughput assays. The importance of this work is attested by the numerous combinatorial research units that are now an integral part of most major pharmaceutical companies. 

Solid-phase organic synthesis really began in 1963, when Merrifield [15] used polystyrene resin beads to aid the synthesis of peptides. This was followed in the 1970s by investigations on solid-phase synthesis towards organic compounds by Leznoff, Camps, Frechet, Rapaport and others [64-67]. 

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