Peptide Alkyl Thioester Synthesis from Advanced Thiols and Peptide Hydrazides.

Peptide alkyl thioesters are versatile reagents in various synthetic applications, commonly generated from peptide hydrazides and thiols. However, a notable limitation is the need for a substantial excess of the thiol reagent, restricting the usage to simple thiols. Here, we introduce an adapted procedure that significantly enhances thioester production with just a minimal thiol excess, facilitating the use of advanced thiol nucleophiles.

Electrostatic Assistance of 4-Mercaptophenylacetic Acid-Catalyzed Native Chemical Ligation.

4-Mercaptophenylacetic acid (MPAA) is a popular catalyst of the native chemical ligation (NCL) but has to be used in large excess for achieving practically useful rates (up to 50-100 equiv). We report here that the catalytic potency of MPAA can be boosted by introducing a stretch of arginines in the departing thiol from the thioester. By doing so, the electrostatically assisted NCL reaction proceeds rapidly by using substoichiometric concentrations of MPAA, an advantage that enables useful synthetic applications.

A biomimetic electrostatic assistance for guiding and promoting N-terminal protein chemical modification.

The modification of protein electrostatics by phosphorylation is a mechanism used by cells to promote the association of proteins with other biomolecules. In this work, we show that introducing negatively charged phosphoserines in a reactant is a powerful means for directing and accelerating the chemical modification of proteins equipped with oppositely charged arginines. While the extra charged amino acid residues induce no detectable affinity between the reactants, they bring site-selectivity to a reaction that is otherwise devoid of such a property.

Redox-Controlled Chemical Protein Synthesis: Sundry Shades of Latency.

The last two decades have witnessed the rise in power of chemical protein synthesis to the point where it now constitutes an established corpus of synthetic methods efficiently complementing biological approaches. One factor explaining this spectacular evolution is the emergence of a new class of chemoselective reactions enabling the formation of native peptide bonds between two unprotected peptidic segments, also known as native ligation reactions. In recent years, their application has fueled the production of homogeneous batches of large and highly decorated protein targets with a control of their composition at the atomic level.

Catalysis of Hydrazone and Oxime Peptide Ligation by Arginine.

Hydrazone and oxime peptide ligations are catalyzed by arginine. The catalysis is assisted intramolecularly by the side-chain guanidinium group. Hydrazone ligation in the presence of arginine proceeds efficiently in phosphate buffer at neutral pH but is particularly powerful in bicarbonate/CO buffer.

A cysteine selenosulfide redox switch for protein chemical synthesis.

The control of cysteine reactivity is of paramount importance for the synthesis of proteins using the native chemical ligation (NCL) reaction. We report that this goal can be achieved in a traceless manner during ligation by appending a simple N-selenoethyl group to cysteine. While in synthetic organic chemistry the cleavage of carbon-nitrogen bonds is notoriously difficult, we describe that N-selenoethyl cysteine (SetCys) loses its selenoethyl arm in water under mild conditions upon reduction of its selenosulfide bond.

Accelerated microfluidic native chemical ligation at difficult amino acids toward cyclic peptides.

Cyclic peptide-based therapeutics have a promising growth forecast that justifies the development of microfluidic systems dedicated to their production, in phase with the actual transitioning toward continuous flow and microfluidic technologies for pharmaceutical production. The application of the most popular method for peptide cyclization in water, i.e.

Improved Outcome by Adding Concurrent Chemotherapy to Cetuximab and Radiotherapy for Locally Advanced Head and Neck Carcinomas: Results of the GORTEC 2007-01 Phase III Randomized Trial.

Purpose To investigate the effect of adding concurrent chemotherapy (CT) to cetuximab plus radiotherapy (RT; CT-cetux-RT) compared with cetuximab plus RT (cetux-RT) in locally advanced squamous cell carcinoma of the head and neck (LA-SCCHN). Patients and Methods In this phase III randomized trial, patients with N0-2b, nonoperated, stage III or IV (nonmetastatic) LA-SCCHN were enrolled. Patients received once-daily RT up to 70 Gy with weekly cetuximab or with weekly cetuximab and concurrent carboplatin and fluorouracil (three cycles).

Accelerating chemoselective peptide bond formation using bis(2-selenylethyl)amido peptide selenoester surrogates.

Given the potential of peptide selenoesters for protein total synthesis and the paucity of methods for the synthesis of these sensitive peptide derivatives, we sought to explore the usefulness of the bis(2-selenylethyl)amido (SeEA) group, the selenium analog of the bis(2-sulfanylethyl)amido (SEA) group, for accelerating peptide bond formation. A chemoselective exchange process operating in water was devised for converting SEA peptides into the SeEA ones. Kinetic studies show that SeEA ligation, which relies on an initial ,-acyl shift process, proceeds significantly faster than SEA ligation.

Semi-synthesis of a HGF/SF kringle one (K1) domain scaffold generates a potent MET receptor agonist.

The development of MET receptor agonists is an important goal in regenerative medicine, but is limited by the complexity and incomplete understanding of its interaction with HGF/SF (Hepatocyte Growth Factor/Scatter Factor). NK1 is a natural occurring agonist comprising the N-terminal (N) and the first kringle (K1) domains of HGF/SF. In the presence of heparin, NK1 can self-associate into a "head to tail" dimer which is considered as the minimal structural module able to trigger MET dimerization and activation whereas isolated K1 and N domains showed a weak or a complete lack of agonistic activity respectively.

One-pot chemical synthesis of small ubiquitin-like modifier protein-peptide conjugates using bis(2-sulfanylethyl)amido peptide latent thioester surrogates.

Small ubiquitin-like modifier (SUMO) post-translational modification (PTM) of proteins has a crucial role in the regulation of important cellular processes. This protocol describes the chemical synthesis of functional SUMO-peptide conjugates. The two crucial stages of this protocol are the solid-phase synthesis of peptide segments derivatized by thioester or bis(2-sulfanylethyl)amido (SEA) latent thioester functionalities and the one-pot assembly of the SUMO-peptide conjugate by a sequential native chemical ligation (NCL)/SEA native peptide ligation reaction sequence.

Access to large cyclic peptides by a one-pot two-peptide segment ligation/cyclization process.

The use of the N-acetoacetyl protecting group for N-terminal cysteine residue enabled creation of an efficient and mild one-pot native chemical ligation/SEA ligation sequence giving access to large cyclic peptides.

Selenopeptide transamidation and metathesis.

Selenopeptides can be transamidated by cysteinyl peptides in water using mild conditions (pH 5.5, 37 °C) in the presence of an arylthiol catalyst. Similar conditions also catalyze the metathesis of selenopeptides.

Phenylthiocarbamate or N-carbothiophenyl group chemistry in peptide synthesis and bioconjugation.

The design of novel chemoselective and site-specific ligation methods provides new tools for obtaining complex scaffolds, peptidomimetics, and peptide conjugates. The chemistry of the N-phenylthiocarbonyl group has led to several developments in peptide ligation chemistry and peptide bioconjugation during the last 10 years. The aim of this review is to provide an overview of this emerging field.

Tidbits for the synthesis of bis(2-sulfanylethyl)amido (SEA) polystyrene resin, SEA peptides and peptide thioesters.

Protein total chemical synthesis enables the atom-by-atom control of the protein structure and therefore has a great potential for studying protein function. Native chemical ligation of C-terminal peptide thioesters with N-terminal cysteinyl peptides and related methodologies are central to the field of protein total synthesis. Consequently, methods enabling the facile synthesis of peptide thioesters using Fmoc-SPPS are of great value.

Exploration of an imide capture/N,N-acyl shift sequence for asparagine native peptide bond formation.

Imide capture of a C-terminal peptidylazide with a side-chain thioacid derivative of an N-terminally protected aspartyl peptide leads to the formation of an imide bond bringing the two peptide ends into close proximity. Unmasking of the N(α) protecting group and intramolecular acyl migration results in the formation of a native peptide bond to asparagine.

High frequency targeted mutagenesis using engineered endonucleases and DNA-end processing enzymes.

Targeting DNA double-strand breaks is a powerful strategy for gene inactivation applications. Without the use of a repair plasmid, targeted mutagenesis can be achieved through Non-Homologous End joining (NHEJ) pathways. However, many of the DNA breaks produced by engineered nucleases may be subject to precise re-ligation without loss of genetic information and thus are likely to be unproductive.

Sequential native peptide ligation strategies for total chemical protein synthesis.

Total chemical synthesis of proteins is usually achieved by assembling unprotected peptide segments using site-specific and chemoselective native peptide ligation methods. Access to large proteins often requires the assembly of at least three segments due to the current limits of solid phase synthesis of individual peptide segments. The aim of this tutorial review is to present the basic concepts and challenges underlying the design of sequential peptide ligation strategies using solution or solid phase chemistry.

Synthesis of peptide alkylthioesters using the intramolecular N,S-acyl shift properties of bis(2-sulfanylethyl)amido peptides.

The design of novel methods giving access to peptide alkylthioesters, the key building blocks for protein synthesis using Native Chemical Ligation, is an important area of research. Bis(2-sulfanylethyl)amido peptides (SEA peptides) 1 equilibrate in aqueous solution with S-2-(2-mercaptoethylamino)ethyl thioester peptides 2 through an N,S-acyl shift mechanism. HPLC was used to study the rate of equilibration for different C-terminal amino acids and the position of equilibrium as a function of pH.

Synthesis of thiazolidine thioester peptides and acceleration of native chemical ligation.

Thiazolidine thioester peptides were synthesized by reacting bis(2-sulfanylethyl)amido peptides with glyoxylic acid at pH 1. A significant increase in Native Chemical Ligation (NCL) rate was observed with thiazolidine thioesters compared to 3-mercaptopropionic acid-thioester analogues. The method is of particular interest for accelerating valine-cysteine peptide bond formation.

Bis(2-sulfanylethyl)amino native peptide ligation.

The reaction of a peptide featuring a bis(2-sulfanylethyl)amino (SEA) group on its C-terminus with a cysteinyl peptide in water at pH 7 and 37 °C leads to the chemoselective and regioselective formation of a native peptide bond. This method called SEA ligation enriches the native peptide ligation repertoire available to the peptide chemist. Preparation of an innovative solid support which allows the straightforward synthesis of peptide SEA fragments using standard Fmoc/tert-butyl solid phase peptide synthesis procedures is also described.

Synthesis of peptide-protein conjugates using N-succinimidyl carbamate chemistry.

Peptide-protein conjugates are useful tools in different fields of research as, for instance, the development of vaccines and drugs or for studying biological mechanisms, to cite only few applications. N-Succinimidyl carbamate (NSC) chemistry has been scarcely used in this area. We show that unprotected peptides, featuring one lysine residue within their sequences, can be converted in good yield into NSC derivatives by reaction with disuccinimidylcarbonate (DSC).

Silver-catalyzed azaGly ligation. Application to the synthesis of azapeptides and of lipid-peptide conjugates.

Glycine is a amino acid frequently found in peptides. Substitution of a glycine residue by an azaglycine allows the modulation of peptide conformation, bioactivity, or stability. Azapeptides are usually prepared using solid-phase synthetic procedures.