Solid phase peptide synthesis cycles

Scheme 20.1. Solid-phase peptide synthesis cycle.

One of the very first papers reporting about endo-linkers was published by Elmore et al. (Scheme 10.4) [13]. They described a new linker containing a phos-phodiester group (19) for solid-phase peptide synthesis using a Pepsyn K (polyacrylamide) resin. After completion of coupling and deprotection cycles, the phos-phodiester (20) was cleaved with a phosphodiesterase. In this way / -casomorphin. Leu-enkephalin and a collagenase substrate (21) were synthesized in high yields. 

The ability to synthesize chemically short sequences of single-stranded DNA (oligonucleotides) is an essential part of many aspects of genetic engineering. The method most frequently employed is that of solid-phase synthesis, where the basic philosophy is the same as that in solid-phase peptide synthesis (see Section 13.6.3). In other words, the growing nucleic acid is attached to a suitable solid support, protected nucleotides are supplied in the appropriate sequence, and each addition is followed by repeated coupling and deprotection cycles. 

Solid-phase peptide synthesis is based on the sequential addition of protected amino acids onto an insoluble support. Addition proceeds from carboxy terminus to amino terminus. The first amino acid is attached to a solid support by a linker and, if necessary, side-chain amino acid function is protected throughout chain assembly. The carboxy group of the in-coming, acylating amino acid is activated for coupling while its amino group is protected temporarily for each coupling step and then deprotected for the next cycle. The... 

Like the solid phase peptide synthesis, this process has also been automated. Commercial automated synthesizers are available that can prepare polynucleotides containing more than 150 bases with a cycle time of about 10 minutes per base. 

Several syntheses of the peptide have been reported by solution methods (74-76). After the introduction of solid-phase peptide synthesis, Marshall and Merrifield conducted the first study of the synthesis of the peptide by using the new technique (77). A -Boc chemistry was used, and Merrifield resin was selected as the solid support. The side chain protections were as follows His, Arg, and Asp were protected by Bn groups Arg by a NO2 group. The Phe was esterified onto the resin in ethanol with the presence of 1 equivalent of triethylamine. The symmetric anhydride method was used for the coupling of the amino acids, and DCC was the coupling reagent. The following cycle of reactions was used to introduce each new residue (Table 7) ... 

Table 1 Overall Synthetic Yield as a Function of the Peptide Length and the Mean Yield per Synthetic Cycle for Linear Solid-Phase Peptide Synthesis...

In solid phase peptide synthesis (SPPS), deletion sequences are generated at each addition of amino acid due to non-quantitative coupling reactions. Their concentration increases exponentially with the length of the peptide chain, and after many cycles not only do they represent a large proportion of the crude preparation, but they can also exhibit physicochemical characteristics similar to the target sequence. Thus, these deletion-sequence contaminants present major problems for removal, or even detection. 

First, a peptide synthesizer was modified to allow solid-phase oligosaccharide synthesis. This platform had the basic function of an automated synthesizer and allowed repeating cycles of glycosylation and deprotection to be mostly software controlled (Fig. 7.2a) [38], This robust pressure-driven system relies on an established... 

The steps in the Merrifield solid-phase peptide and protein synthesis attachment of an amino acid to a polymer head followed hy cycles of attachment of other amino acids allows extremely high yield syntheses at each step and acceptable yields for syntheses that exceed 100 amino acid condensations. 

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