Thiol-thioester Exchange Research Articles

Aggregation Behavior and Thiol-Thioester Exchange for Cationic Surfactants with Propylthioacetate Side Chain.

A series of cationic surfactants containing the thioacetate group, [CnH2n+1N(CH3)2(CH2)3SCOCH3] Cl (Cn3SAc, n = 12, 14, 16), were prepared and their properties in aqueous solution were investigated by conductivity, fluorescence, and dynamic light scattering measurements. The critical micelle concentrations (CMCs) of Cn3SAc decreased to about half the value of the corresponding alkyltrimethylammonium chloride. Thioacetate was eliminated with the addition of dithiothreitol (DTT) as well as NaOH. HPLC (high performance liquid chromatography) analysis and NMR (nuclear magnetic resonance) spectroscopy showed that thiol surfactants, [CnH2n+1N(CH3)2(CH2)3SH]Cl (Cn3SH), were generated upon the addition of DTT in aqueous solution via thiol-thioester exchange, whereas gemini surfactants, [CnH2n+1N(CH3)2(CH2)3SS(CH2)3N(CH3)2CnH2n+1]2Cl (2Cn3SS), were generated upon incubation in alkaline solution via hydrolysis and air oxidation.

Recyclable and repolymerizable thiol–X photopolymers

Truly recyclable and repolymerizable photopolymers were achieved by utilizing thiol–ene polymerization and thiol–thioester exchange reactions.

Production of dynamic lipid bilayers using the reversible thiol-thioester exchange reaction.

Thiol lysolipids undergo thiol-thioester exchange with two phenyl thioester-functionalized tails to produce phospholipid structures that assemble into liposomes with differences in exchange rates, temperature sensitivity, permeability, and continued exchange behavior. This in situ formation reaction imparts dynamic characteristics into the membrane for downstream liposome functionalization and mimics native membrane remodeling.

A user's guide to the thiol-thioester exchange in organic media: scope, limitations, and applications in material science

The dynamic exchange of thiols and thioesters in organic media was explored, leading to room temperature plasticity in crosslinked polymers.

On-Demand Dissolution of Chemically Cross-Linked Hydrogels.

The formation and subsequent on-demand dissolution of chemically cross-linked hydrogels is of keen interest to chemists, engineers, and clinicians. In this Account, we summarize our recent advances in the area of dissolvable chemically cross-linked hydrogels and provide a comparative discussion of other recent hydrogel systems. Using biocompatible macromonomers, we developed a library of cross-linked dendritic hydrogels that possess favorable properties, including biocompatibility, tissue adhesion, and swelling. Additionally, these hydrogels possess the unique ability to dissolve on-demand via application of a biocompatible aqueous solution. Each of the three hydrogel systems described employs a thiol-thioester exchange reaction as the mechanism of dissolution. These new materials successfully decrease bleeding in in vivo models of hepatic and aortic hemorrhage and dissolve on-demand, providing easy removal. In addition, we evaluated these hydrogels as dressings for second-degree burn wounds and performed proof-of-concept in vivo studies. These hydrogel wound dressings provide a means of repeatedly changing the dressing in a minimally invasive and atraumatic manner while also serving as a protective barrier against bacterial infection. Finally, we highlight the seminal work of other researchers in the field of dissolvable chemically cross-linked hydrogels using thiol-disulfide exchange, retro-Michael-type, and retro-Diels-Alder reactions. These chemistries provide a versatile synthetic toolbox to dissolve hydrogels in a controlled manner on time scales from minutes to weeks. Continued investigation of these dissolution approaches as well as the development of new chemical reactions will open doors to other avenues of on-demand dissolution and expand the application space for these materials. In summary, the management and closure of wounds after traumatic injury or surgical intervention are of significant clinical importance. Stimuli-responsive hydrogels that function as sealants, adhesives, or dressings are emerging as vital alternatives to current standards of care that rely upon conventional sutures, staples, or dressings.

Dynamic glycosylation of liposomes by thioester exchange.

The interplay of dynamic functionalization and specific molecular recognition on biological membranes is key to numerous physiological processes. In this work we present a simple glycocalyx model based on the covalent yet reversible glycosylation of liposomes and subsequent recognition by a lectin. Reversible thioester exchange of membrane embedded amphiphilic thioesters with thiol-tagged d-mannose in solution is performed at physiologically relevant conditions. Recognition with the lectin concanavalin A is possible directly from this reaction mixture, leading to liposome agglutination. To the best of our knowledge, the dynamic covalent glycosylation of liposomes is so far unprecedented.

On-Demand Dissolution of a Dendritic Hydrogel-based Dressing for Second-Degree Burn Wounds through Thiol-Thioester Exchange Reaction.

An adhesive yet easily removable burn wound dressing represents a breakthrough in second-degree burn wound care. Current second-degree burn wound dressings absorb wound exudate, reduce bacterial infections, and maintain a moist environment for healing, but are surgically or mechanically debrided from the wound, causing additional trauma to the newly formed tissues. We have developed an on-demand dissolvable dendritic thioester hydrogel burn dressing for second-degree burn care. The hydrogel is composed of a lysine-based dendron and a PEG-based crosslinker, which are synthesized in high yields. The hydrogel burn dressing covers the wound and acts as a barrier to bacterial infection in an in vivo second-degree burn wound model. A unique feature of the hydrogel is its capability to be dissolved on-demand, via a thiol-thioester exchange reaction, allowing for a facile burn dressing removal.

On‐Demand Dissolution of a Dendritic Hydrogel‐based Dressing for Second‐Degree Burn Wounds through Thiol–Thioester Exchange Reaction

AbstractAn adhesive yet easily removable burn wound dressing represents a breakthrough in second‐degree burn wound care. Current second‐degree burn wound dressings absorb wound exudate, reduce bacterial infections, and maintain a moist environment for healing, but are surgically or mechanically debrided from the wound, causing additional trauma to the newly formed tissues. We have developed an on‐demand dissolvable dendritic thioester hydrogel burn dressing for second‐degree burn care. The hydrogel is composed of a lysine‐based dendron and a PEG‐based crosslinker, which are synthesized in high yields. The hydrogel burn dressing covers the wound and acts as a barrier to bacterial infection in an in vivo second‐degree burn wound model. A unique feature of the hydrogel is its capability to be dissolved on‐demand, via a thiol–thioester exchange reaction, allowing for a facile burn dressing removal.

Theoretical investigations on the thiol–thioester exchange steps of different thioesters

As the rate-determining step in native chemical ligation reactions, the thiol–thioester exchange step is important in determining the efficiency of the ligations of peptides. In the present study, systematic theoretical calculations were carried out on the relationships between the structure of different thioesters and the free energy barriers of the thiol–thioester exchange step. According to the calculation results, the thiol–thioester exchange step is disfavored by the steric hindrance around the carbonyl center, while the electronic effect (i.e. conjugation and hyper-conjugation effects) becomes important when the steric hindrance is insignificant.

New insights into the posttranslational regulation of human cytosolic thioredoxin by S-palmitoylation

High level of palmitate is associated with metabolic disorders. We recently showed that enhanced level of S-palmitoylated cytosolic thioredoxin (Trx1) in mouse liver was new characteristic feature of insulin resistance. However, our understanding of the effect of S-palmitoylation on Trx1 is limited, and the tissue specificity of Trx1 S-palmitoylation is unclear. Here we show that S-palmitoylation also occurs at Cys73 of Trx1 in living endothelial cells, and the level of S-palmitoylated Trx1 undergoes regulation by insulin signaling. Trx1 prefers thiol-thioester exchange with palmitoyl-CoA to acetyl-CoA. S-palmitoylation alters conformation or secondary structure of Trx1, as well as decreases the ability of Trx1 to transfer electrons from thioredoxin reductase to S-nitrosylated protein–tyrosine phosphatase 1B and S-nitroso-glutathione. Our results demonstrate that S-palmitoylation is an important post-translational modification of human Trx1.

Competition and cooperation in dynamic replication networks.

The simultaneous replication of six coiled-coil peptide mutants by reversible thiol-thioester exchange reactions is described. Experimental analysis of the time dependent evolution of networks formed by the peptides under different conditions reveals a complex web of molecular interactions and consequent mutant replication, governed by competition for resources and by autocatalytic and/or cross-catalytic template-assisted reactions. A kinetic model, first of its kind, is then introduced, allowing simulation of varied network behaviour as a consequence of changing competition and cooperation scenarios. We suggest that by clarifying the kinetic description of these relatively complex dynamic networks, both at early stages of the reaction far from equilibrium and at later stages approaching equilibrium, one lays the foundation for studying dynamic networks out-of-equilibrium in the near future.

A dendritic thioester hydrogel based on thiol-thioester exchange as a dissolvable sealant system for wound closure.

Washable wound dressing: A dissolvable dendritic thioester hydrogel for wound closure has been developed. The hydrogel sealant adheres strongly to tissues, closes an ex vivo vein puncture, and withstands high pressures placed on a wound. This material can be washed off upon exposure to thiolates because a thiol–thioester exchange takes place, and gradual wound re-exposure may be achieved during surgical care.

A Dendritic Thioester Hydrogel Based on Thiol–Thioester Exchange as a Dissolvable Sealant System for Wound Closure

Abwaschbarer Wundverschluss: Ein auflösbares dendritisches Thioester-Hydrogel zum Wundverschluss wurde entwickelt. Dieses haftet fest an Geweben, schließt eine Venenpunktion ex vivo und hält hohen Drücken stand. Das Material kann durch die Zugabe von Thiolaten abgewaschen werden, da ein Thiol-Thioester-Austausch stattfindet, sodass die graduelle Wiederöffnung der Wunde während einer operativen Versorgung ermöglicht wird.

A Thioethylalkylamido (TEA) Thioester Surrogate in the Synthesis of a Cyclic Peptide via a Tandem Acyl Shift

The cyclic cystine-knot peptide, kalata B1, was synthesized by employing a novel Fmoc-compatible thioethylalkylamido (TEA) thioester surrogate via an N-S acyl shift followed by a thiol-thioester exchange reaction. TEA thioester surrogate is cost-effective, conveniently prepared in one-step with starting materials, readily available from commercial sources, and highly efficient in preparing peptide thioesters.

Orbital Interactions in Native Chemical Ligation Reaction of Proline Thioesters

A systematic theoretical study was carried out to investigate the origin of the relatively low reactivity of peptide-prolyl-thioesters in the native chemical ligation(NCL) reaction. Mechanistic calculations were performed on the two NCL reactions of peptide-prolyl-thioester(Path-Pro) and peptidealanyl-thioester(Path-Ala). The results show that both include three steps: intermolecular thiol-thioester exchange, transthioesterification, and a final intramolecular S→N acyl migration. The calculations indicate that the first step is the rate determining step of both pathways. Path-Pro is kinetically disfavored, so the peptide-prolyl-thioester is found to be less reactive in NCL reaction. This conclusion is consistent with the experimental observations. Further examination of the rate determining steps of these two pathways shows that the n→π* interaction of prolineαN carbonyl increases the LUMO orbital energy of peptidyl- prolylthioester, decreases the interaction energy between proline carbonyl and the sulphur atom in aryl thiol, and finally increases the total energy barrier.

Ｎ‐Ｓアシル基転位反応を用いるペプチドチオエステル合成法の開発

Peptide thioesters are used as key building blocks for contemporary protein synthesis, based on the ligation strategy such as thioester method and native chemical ligation. We found the methods for preparation of the peptide thioesters, in which the key reaction is an intramolecular N-S acyl shift reaction of thiol-containing peptides. These processes can be applied to Fmoc based solid phase peptide synthesis with minimum racemization at the thioester position. For the N-S acyl shift reaction, we use an N-2-mercapto-4,5-dimethoxybenzyl (Dmmb) group on the peptide bond, or a cysteine residue. The Dmmb-containing peptide is readily converted to the corresponding 2-sulfoethyl thioester via the N-S acyl shift reaction, followed by the intermolecular thiol-thioester exchange reaction. A peptide containing a Cys-Pro ester (CPE) moiety is spontaneously transformed into a diketopiperazine (DKP) thioester under neutral conditions. Furthermore, a peptide containing a Cys-Pro-Cys (CPC) sequence was also transformed into a peptide DKP thioester under acidic conditions via the N-S acyl shift reaction.

The relative rates of thiol-thioester exchange and hydrolysis for alkyl and aryl thioalkanoates in water.

This article reports rate constants for thiol-thioester exchange (k (ex)), and for acid-mediated (k (a)), base-mediated (k (b)), and pH-independent (k (w)) hydrolysis of S-methyl thioacetate and S-phenyl 5-dimethylamino-5-oxo-thiopentanoate-model alkyl and aryl thioalkanoates, respectively-in water. Reactions such as thiol-thioester exchange or aminolysis could have generated molecular complexity on early Earth, but for thioesters to have played important roles in the origin of life, constructive reactions would have needed to compete effectively with hydrolysis under prebiotic conditions. Knowledge of the kinetics of competition between exchange and hydrolysis is also useful in the optimization of systems where exchange is used in applications such as self-assembly or reversible binding. For the alkyl thioester S-methyl thioacetate, which has been synthesized in simulated prebiotic hydrothermal vents, k (a) = 1.5 × 10(-5)M(-1) s(-1), k (b) = 1.6 × 10(-1)M(-1) s(-1), and k (w) = 3.6 × 10(-8)s(-1). At pH7 and 23°C, the half-life for hydrolysis is 155days. The second-order rate constant for thiol-thioester exchange between S-methyl thioacetate and 2-sulfonatoethanethiolate is k (ex) = 1.7M(-1)s(-1). At pH7 and 23°C, with [R″S(H)] = 1mM, the half-life of the exchange reaction is 38h. These results confirm that conditions (pH, temperature, pK (a) of the thiol) exist where prebiotically relevant thioesters can survive hydrolysis in water for long periods of time and rates of thiol-thioester exchange exceed those of hydrolysis by several orders of magnitude.

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. We show also that thioester form 2 can participate efficiently in a thiol-thioester exchange reaction with 5% aqueous 3-mercaptopropionic acid. The highest reaction rate was obtained at pH 4. These experimental conditions are significantly less acidic than those reported in the past for related systems. The method was validated with the synthesis of a 24-mer peptide thioester. Consequently, SEA peptides 1 constitute a powerful platform for access to native chemical ligation methodologies.

Theoretical Analysis of the Detailed Mechanism of Native Chemical Ligation Reactions

The method of native chemical ligation between an unprotected peptide α-thioester and an N-terminal cysteine-peptide to give a native peptide in aqueous solution is one of the most effective peptide ligation methods. In this work, a systematic theoretical study was carried out to fully understand the detailed mechanism of ligation. It was found that for the conventional native chemical ligation reaction between a peptide thioalkyl ester and a cysteine in combination with an added aryl thiol as catalyst, both the thiol-thioester exchange step and the transthioesterification step proceed by an anionic concerted S(N)2 displacement mechanism, whereas the intramolecular rearrangement proceeds by an addition-elimination mechanism, and the rate-limiting step is the thiol-thioester exchange step. The theoretical method was then extended to study the detailed mechanism of the auxiliary-mediated peptide ligation between a peptide thiophenyl ester and an N-2-mercaptobenzyl peptide in which both the thiol-thioester exchange step and intramolecular acyl-transfer step proceed by a concerted S(N)2-type displacement mechanism. The energy barrier of the thiol-thioester exchange step depends on the side-chain steric hindrance of the C-terminal amino acid, whereas that of the acyl-transfer step depends on the side-chain steric hindrance of the N-terminal amino acid.

Side-Chain Pairing Preferences in the Parallel Coiled-Coil Dimer Motif: Insight on Ion Pairing between Core and Flanking Sites

A new strategy for rapid evaluation of sequence-stability relationships in the parallel coiled-coil motif is described. The experimental design relies upon thiol-thioester exchange equilibria, an approach that is particularly well suited to examination of heterodimeric systems. Our model system has been benchmarked by demonstrating that it can quantitatively reproduce previously reported trends in interhelical a-a' side-chain pairing preferences at the coiled-coil interface. This new tool has been used to explore the role of Coulombic interactions between a core position on one helix and a flanking position on the other helix (a-g'). This type of interhelical contact has received relatively little attention to date. Our results indicate that such interactions can influence coiled-coil partner preferences.