Single addition of an allyl amine monomer enables access to end-functionalized RAFT polymers via native chemical ligation

A novel method for the introduction of a single protected amine-functional monomer at the chain end of RAFT polymers has been developed. This monomer addition, in concert with native chemical ligation, facilitated the development of a simple and versatile method for the end-functionalisation of polymers with peptides

Peptide Ligation–Desulfurization Chemistry at Arginine

The utility of a new β‐thiol arginine building block in ligation–desulfurization chemistry has been demonstrated through reactions and kinetic studies with a range of peptide thioesters. Application of the method is highlighted by a one‐pot, kinetically controlled, rapid ligation to generate a 7 kDa MUC1 glycopeptide

Rapid Additive-Free Selenocystine–Selenoester Peptide Ligation

We describe an unprecedented reaction between peptide selenoesters and peptide dimers bearing N-terminal selenocystine that proceeds in aqueous buffer to afford native amide bonds without the use of additives. The selenocystine-selenoester ligations are complete in minutes, even at sterically hindered junctions, and can be used in concert with one-pot deselenization chemistry. Various pathways for the transformation are proposed and probed through a combination of experimental and computational studies. Our new reaction manifold is also showcased in the total synthesis of two proteins

Site-Selective Solid-Phase Synthesis of a CCR5 Sulfopeptide Library To Interrogate HIV Binding and Entry

Tyrosine (Tyr) sulfation is a common post-translational modification that is implicated in a variety of important biological processes, including the fusion and entry of human immunodeficiency virus type-1 (HIV-1). A number of sulfated Tyr (sTyr) residues on the N-terminus of the CCR5 chemokine receptor are involved in a crucial binding interaction with the gp120 HIV-1 envelope glycoprotein. Despite the established importance of these sTyr residues, the exact structural and functional role of this post-translational modification in HIV-1 infection is not fully understood. Detailed biological studies are hindered in part by the difficulty in accessing homogeneous sulfopeptides and sulfoproteins through biological expression and established synthetic techniques. Herein we describe an efficient approach to the synthesis of sulfopeptides bearing discrete sulfation patterns through the divergent, site-selective incorporation of sTyr residues on solid support. By employing three orthogonally protected Tyr building blocks and a solid-phase sulfation protocol, we demonstrate the synthesis of a library of target N-terminal CCR5(2-22) sulfoforms bearing discrete and differential sulfation at Tyr10, Tyr14, and Tyr15, from a single resin-bound intermediate. We demonstrate the importance of distinct sites of Tyr sulfation in binding gp120 through a competitive binding assay between the synthetic CCR5 sulfopeptides and an anti-gp120 monoclonal antibody. These studies revealed a critical role of sulfation at Tyr14 for binding and a possible additional role for sulfation at Tyr10. N-terminal CCR5 variants bearing a sTyr residue at position 14 were also found to complement viral entry into cells expressing an N-terminally truncated CCR5 receptor

Recent extensions to native chemical ligation for the chemical synthesis of peptides and proteins

Native chemical ligation continues to play a pivotal role in the synthesis of increasingly complex peptide and protein targets twenty years after its initial report. This opinion article will highlight a number of recent, powerful extensions of the technology that have expanded the scope of the reaction, accelerated ligation rates, enabled chemoselective post-ligation modifications, and streamlined the ligation of multiple peptide fragments. These advances have facilitated the synthesis of a number of impressive protein targets to date and hold great promise for the continued application of native chemical ligation for the detailed study of protein structure and function

Synthesis and Utility of β-Selenol-Phenylalanine for Native Chemical Ligation–Deselenization Chemistry

An efficient synthetic route to a suitably protected β-selenol-phenylalanine derivative from commercially available Garner’s aldehyde is described. The incorporation of this building block into peptides and its application in native chemical ligation reactions with peptide thioesters are demonstrated. Ligation products were chemoselectively deselenized (including in the presence of unprotected cysteine residues) to provide native peptides

Peptide ligation chemistry at selenol amino acids

The convergent assembly of peptide fragments by native chemical ligation has revolutionized the way in which proteins can be accessed by chemical synthesis. A variation of native chemical ligation involves the reaction of peptides bearing an N‐terminal selenocysteine residue with peptide thioesters, which proceeds through the same mechanism as the parent reaction. This transformation was first investigated in 2001 for the installation of selenocysteine into peptides and proteins via ligation chemistry. The recent discovery that selenocysteine residues within peptides can be chemoselectively deselenized without the concomitant desulfurization of cysteine residues has led to renewed interest in ligation chemistry at selenocysteine. This review outlines the use of selenocysteine in ligation chemistry as well as recent investigations of chemoselective ligation–deselenization chemistry at other selenol‐derived amino acids that have the potential to greatly expand the number of targets that can be accessed by chemical synthesis. Copyright © 2013 European Peptide Society and John Wiley & Sons, Ltd

Synthesis of β-Thiol Phenylalanine for Applications in One-Pot Ligation- Desulfurization Chemistry

The efficient synthesis of a β-thiol phenylalanine derivative is described starting from Garner’s aldehyde. The utility of this amino acid in peptide ligation–desulfurization chemistry is described, including the trifluoroethanethiol (TFET)-promoted one-pot assembly of the 62 residue peptide hormone augurin

Synthesis of MUC1-lipopeptide chimeras

An efficient method for the convergent assembly of MUC1-lipopeptide vaccine candidates is described. Chimeras consisting of MUC1 glycopeptides (bearing multiple copies of the TN and T tumour-associated carbohydrate antigens) tethered to the lipopeptide immunoadjuvant Pam3CysSer were synthesised in high yields using a fragment-based condensation strategy