Techniques for the Facilitation of Peptide Synthesis

Abstract

Synthesis of a peptide chain comprising a large number of amino acid residues can be a difficult task and proteins with over a hundred, and sometimes hundreds of, residues are formidable objectives. The steps of protection, coupling, deprotection, isolation and characterization of the intermediates is not only a time-consuming but also a discouragingly repetitive endeavor. An additional source of frustration is the scarcity of solvents suitable for reactions with high molecular weight intermediates. Such difficulties led to a search for techniques which can alleviate the burden of peptide chemists, for methods which can facilitate the building of long peptide chains from amino acids. The repetitive character of chain lengthening with active esters prompted speculations [1] about the mechanization of peptide synthesis. The first realization of such ideas came from Merrifield [2] and, simultaneously, from Letsinger and Komet [3]. In both methods an amino acid is attached to an insoluble polymeric support and the subsequent operations are carried out on the peptidic material linked to the resin. The version proposed by Merrifield [2] developed into a major discipline, solid phase peptide synthesis. One of the most conspicuous characteristics of the new technique is that it stimulated further thoughts toward improvements to an unprecedented extent. Research grew in this area in an exponential manner and has been reviewed repeatedly. A comprehensive review of solid phase peptide synthesis by Barany and Merrifield [4] required almost 300 pages for a full account. The “solid” phase idea permeated other fields as well and is used now, with considerable success, in the sequencing of proteins and in the synthesis of oligo- and polynucleotides. In this chapter we give only the outlines of solid phase peptide synthesis because two monographs [4] deal with numerous aspects of this rapidly growing area of research.