Year: 2014
Type: article
Abstract: Posttranslational modifications (PTMs) are ubiquitous chemical alterations that are made to peptides and proteins after ribosomal synthesis. The non-templated nature of PTMs hinders the ability to study an individual isoform of a given protein, which may be expressed as complex mixtures in vivo. This thesis describes ligation-based strategies for use in the chemical synthesis of PTM peptides and proteins. Chapter one describes the development of a synthesis of the antibacterial PTM peptide microcin B17 (MccB17). Using Ag(I)-ligation chemistryMccB17 was synthesised efficiently from three precursors. This strategy permitted the synthesis of 7 analogues for use in structure-activity relationship studies. A truncated analogue of MccB17 was shown to be a more potent poison of DNA gyrase, the target of MccB17, compared with MccB17. Chapter two describes ligation–desulfurisation chemistry at β-SH aspartate (Asp). A protected form of β SH Asp was accessed efficiently in 3-steps for direct use in peptide synthesis. Ligation reactions of peptides bearing this amino acid were rapid and ligated products could be desulfurised to afford peptides bearing the native Asp residue in high yields. Computational analysis then prompted exploration of chemoselective desulfurisation of β-SH Asp in the presence of Cys residues. This strategy permitted the synthesis of the N-terminal extracellular domain of CXCR4, bearing a sTyr residue and an N-linked glycan. Chapter three outlines the use of a new alkyl thiol additive for use in one pot ligation–desulfurisation chemistry, namely 2,2,2-trifluoroethanethiol (TFET). This alkyl thiol facilitated ligation rates similar to the current gold standard thiol additives. Importantly, the alkyl nature of TFET allowed desulfurisation to be conducted in the same vessel, a feat not possible with aryl thiol additives. Through the use of TFET, the synthesis of four sulfoforms of the 60 amino acid (sulfo)protein madanin-1 was achieved.
Author: Robert E. Thompson
Language: English
Subfield: Organic Chemistry
Field: Chemistry
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W852251469