Strategy polypeptide synthesis

Abstract This article summarizes recent developments in the synthesis of polypeptides and hybrid peptide copolymers. Traditional methods used to polymerize -amino acid-N-carboxyanhydrides (NCAs) are described, and limitations in the utility of these systems for the preparation of polypeptides are discussed. Recently developed initiators and methods are also discussed that allow polypeptide synthesis with good control over chain length, chain length distribution, and chain-end functionality. The latter feature is particularly useful for the preparation of polypeptide hybrid copolymers. The methods and strategies for the preparation of such hybrid copolymers are described, as well as analysis of the synthetic scope of the different methods. Finally, issues relating to obtaining these highly functional copolymers in pure form are detailed. 

Introduction. 6-Mercapto-4-dibenzofuranol is a reagent developed specifically as an optimal spacing element to facilitate the intramolecular 0,Wacyl transfer during the second stage of the amide-bond-forming protocol known as the thiol capture strategy. As a result, it plays a special role in a relatively new solid phase polypeptide synthesis strategy. 

Strategies for functionalization have been developed that exploit the naturally occurring amino acids as well as the non-natural ones. Post-synthetic modifications have been reported that are based on reactive sites that self catalyze the incorporation of the new functionality at the side chains of Lys residues [24,25] and on the chemoselective ligation reaction [26-29]. These developments in combination with new methodology for the synthesis of large proteins [30] provide access to a highly versatile pool of new polypeptides and proteins. 

On the other hand, pyrenyl-L-alanine 184 has also been used as a conformational probe in the characterization of an artificial 4-a-helix bundle protein.11,121 The 53-residue peptide 186 incorporating one residue of 184 in each of two different helical segments was synthesized by solid-phase synthesis using a segment condensation strategy and the oxime resin. Boc-pyrenyl-L-alanine 191 was coupled just like any other amino acid by the BOP/HOBt method in DMF. CD and fluorescence studies demonstrated that the two pyrene groups were in close proximity forming an excimer complex, which is possible only when the polypeptide chain folds into a 4-a-helix bundle structure. 

Photoaffinity reagents of low molecular weight can be made by total synthesis or by attaching photoactivatable groups to preexisting ligands. For macromolecules, such as polypeptides, only the latter strategy is feasible. 

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