Cysteine Derivatives Research Articles

Cesium (Z)‐2‐Carbomethoxyethenethiolate: A Reagent for the Preparation of (Z)‐2‐Carbomethoxyethenyl Thioethers Including Selected Cysteine and Homocysteine Derivatives

AbstractAs a means to circumvent the standard and sometimes troubling conjugate addition reaction of thiols to alkyl propiolates, a new reagent, cesium (Z)‐2‐carbomethoxyethenethiolate, is introduced. The cesium carbonate mediated methanolysis of (Z)‐2‐carbomethoxyethenyl thiolacetate at low temperature creates cesium (Z)‐2‐carbomethoxyethenethiolate in solution. For base‐insensitive and solvolytically stable electrophiles, efficient substitution can be achieved by direct introduction to the electrophile. The conditions were adapted to accommodate base‐sensitive cysteine derivatives, and the use of DMF as a cosolvent permits the isolation of (Z)‐2‐carbomethoxyethenyl cysteinyl thioethers in high enantiomeric purity (>99:1 er) and with good Z/E ratios. There was no evidence of carbon substitution reactions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

Competition between cleavage and decarboxylation in photolysis of α-carboxy-2-nitrobenzyl protected cysteine derivatives

Photolysis of model peptides containing alpha-carboxy-2-nitrobenzyl (CNB) or alpha-carboxy-4,5-dimethoxy-2-nitrobenzyl (CDMNB) protected cysteines in aqueous solution gives the expected 2-nitrobenzyl-type photocleavage and can be accompanied by photodecarboxylation depending on structural aspects.

Dehydrative cyclization of serine, threonine, and cysteine residues catalyzed by molybdenum(VI) oxo compounds

Commercially available molybdenum(VI) oxides such as (NH 4) 2MoO 4, (NH 4) 6Mo 7O 24·4H 2O, MoO 2(acac) 2, and MoO 2(TMHD) 2 are highly effective dehydrative cyclization catalysts for the synthesis of a variety of oxazolines. The reaction proceeds with a complete retention of configuration at the β-position. For the dehydrative cyclization of cysteine derivatives, bis(2-ethyl-8-quinolinolato)dioxomolybdenum(VI) shows remarkable catalytic activity and gives thiazolines without a significant loss of stereochemical integrity at the C2-exomethine positions.

Surfaces for Immobilization of N-Terminal Cysteine Derivatives via Native Chemical Ligation

This paper presents an improved method for fast, reliable, and quantitative native chemical ligation (NCL--the reaction between an N-terminal cysteine and a thioester to yield an amide bond) at thiophenyl ester-functionalized glass surfaces. For the first time, the degree of surface functionalization has been measured and can be readily controlled by varying the concentration of thiophenyl ester groups on the surface. This methodology facilitates the preparation of tailor-made functionalized glass surfaces for diverse applications. S-Phenyl 11-(chlorodimethylsilyl)-undecanethiolate, and the benzyl analogue, are readily prepared from 10-undecanoic acid via thioester formation and platinum-catalyzed hydrosilylation of the terminal alkene functionality. Thioesters covalently bound to glass surfaces were then formed by submerging clean glass in toluene-solutions of the relevant thioester silylchloride (1%) containing the non-nucleophilic base, ethyldiisopropylamine (1%). NCL was explored with a cysteine-lissamine conjugate, and the degree of surface functionalization was quantified by UV/vis absorption spectroscopy, using the lissamine chromophore. NCL at thiophenyl ester surfaces proved fast (half-life less than 10 min) and yielded levels of surface functionalization consistent with a dense monolayer of dimethyloctylsilane (ca. 2.0 molecules/nm2). Water contact angles on thiophenyl ester surfaces were found to decrease after NCL reaction with the cysteine-lissamine conjugate, whereas surfaces treated with the same buffer solution containing an unreactive alanine-lissamine conjugate showed no significant changes in contact angle, indicating that thioester hydrolysis is not significant during the course of the reaction. NCL with the cysteine-lissamine conjugate at mixed surfaces containing both thiophenyl esters and inert octyl chains showed lower levels of surface functionalization as expected. Plotting the proportion of thiophenyl esters used in the preparation of the substrates against integrated absorption from the surface yielded a linear relationship, demonstrating that NCL on these surfaces occurs in a controllable manner.

Oxidation by chlorine dioxide of methionine and cysteine derivatives to sulfoxides

Methionine and cysteine derivatives were oxidized asymmetrically by chlorine dioxide to sulfinyl derivatives.

A novel approach to enhancing cellular glutathione levels

GSH and GSH-associated metabolism provide the major line of defense for the protection of cells from oxidative and other forms of toxic stress. Of the three amino acids that comprise GSH, cysteine is limiting for GSH synthesis. As extracellularly cysteine is readily oxidized to form cystine, cystine transport mechanisms are essential to provide cells with cysteine. Cystine uptake is mediated by system x(c)(-), a Na(+)-independent cystine/glutamate antiporter. Inhibition of system x(c)(-) by millimolar concentrations of glutamate, a pathway termed oxidative glutamate toxicity, results in GSH depletion and nerve cell death. Recently, we described a series of compounds derived from the conjugation of epicatechin (EC) with cysteine and cysteine derivatives that protected nerve cells in culture from oxidative glutamate toxicity by maintaining GSH levels. In this study, we characterize an additional EC conjugate, cysteamine-EC, that is 5- to 10-fold more potent than the earlier conjugates. In addition, we show that these EC conjugates maintain GSH levels by enhancing the uptake of cystine into cells through induction of a disulfide exchange reaction, thereby uncoupling the uptake from system x(c)(-). Thus, these novel EC conjugates have the potential to enhance GSH synthesis under a wide variety of forms of toxic stress.

Click Azide−Nitrile Cycloaddition as a New Ligation Tool for the Synthesis of Tetrazole-Tethered C-Glycosyl α-Amino Acids

Glycoproteins play a key role in a multitude of biological events in living organisms. Hence, neoglycopeptides obtained from unnatural C-glycosyl alpha-amino acids can be used as synthetic probes in studies aiming at clarifying the role of the carbohydrate domain in glycoprotein biological activity. A new class of C-glycosyl alpha-amino acids featuring a nitrogenated heterocycle ring holding the carbohydrate and glycinyl moiety was designed in our laboratory. Having previously prepared isoxazole-, 1,2,3-triazole-, and pyridine-tethered compounds, the family has now been enlarged by a group of newcomers represented by tetrazole derivatives. Two sets of compounds have been prepared, one being constituted of C-galactosyl and C-ribosyl O-tetrazolyl serines while the other contains S-tetrazolyl cysteine derivatives. In both cases, the synthetic scheme involved a two-step route, the first one being the thermal cycloaddition of a sugar azide with p-toluensulfonyl cyanide (TsCN) to give a 1-substituted 5-sulfonyl tetrazole and the second the replacement of the tosyl group with a serine or cysteine residue. For the high efficiency and operational simplicity, the azide-TsCN cycloaddition appears to be a true click process. Finally, one of the amino acids prepared was incorporated into a tripeptide.

Synthesis of pdCpAs and transfer RNAs activated with derivatives of aspartic acid and cysteine

Described herein is the preparation of new aminoacylated derivatives of the dinucleotide pdCpA, and of transfer RNAs. The focus of the present work is the synthesis of amino acid analogs related to aspartic acid and cysteine species that have important functional roles in many proteins. The activated aminoacyl-tRNAs prepared can be utilized for the elaboration of proteins containing modified aspartic acid and cysteine derivatives at predetermined sites. Of particular interest is definition of functional group protection strategies that can be used for the preparation of the aminoacylated pdCpAs and tRNAs.

Catabolism of Glutathione Conjugates in Arabidopsis thaliana: ROLE IN METABOLIC REACTIVATION OF THE HERBICIDE SAFENER FENCLORIM

The safener fenclorim (4,6-dichloro-2-phenylpyrimidine) increases tolerance to chloroacetanilide herbicides in rice by enhancing the expression of detoxifying glutathione S-transferases (GSTs). Fenclorim also enhances GSTs in Arabidopsis thaliana, and while investigating the functional significance of this induction in suspension cultures, we determined that these enzymes glutathionylated the safener. The resulting S-(fenclorim)-glutathione conjugate was sequentially processed to S-(fenclorim)-gamma-glutamyl-cysteine and S-(fenclorim)-cysteine (FC), the latter accumulating in both the cells and the medium. FC was then either catabolized to 4-chloro-6-(methylthio)-phenylpyrimidine (CMTP) or N-acylated with malonic acid. These cysteine derivatives had distinct fates, with the enzymes responsible for their formation being induced by fenclorim and FC. Fenclorim-N-malonylcysteine was formed from FC by the action of a malonyl-CoA-dependent N-malonyltransferase. A small proportion of the fenclorim-N-malonylcysteine then underwent decarboxylation to yield a putative S-fenclorim-N-acetylcysteine intermediate, which underwent a second round of GST-mediated S-glutathionylation and subsequent proteolytic processing. The formation of CMTP was catalyzed by the concerted action of a cysteine conjugate beta-lyase and an S-methyltransferase, with the two activities being coordinately regulated. Although the fenclorim conjugates tested showed little GST-inducing activity in Arabidopsis, the formation of CMTP resulted in metabolic reactivation, with the product showing good enhancing activity. In addition, CMTP induced GSTs and herbicide-safening activity in rice. The bioactivated CMTP was in turn glutathione-conjugated and processed to a malonyl cysteine derivative. These results reveal the surprisingly complex set of competing catabolic reactions acting on xenobiotics entering the S-glutathionylation pathway in plants, which can result in both detoxification and bioactivation.

A Unique Family of Stable and Water-Soluble S-Nitrosothiol Complexes

In this work, we present a complete and detailed experimental characterization and theoretical study of a variety of coordinated S-nitrosothiols (RSNOs), such as cysteine derivatives, mercaptosuccinic acid, benzyl thiol, and phenyl thiol. Some of them are extremely unstable and sensitive in free form. Strikingly, in contrast with free S-nitrosothiols, we found that, upon coordination to iridium, they become very stable even in aqueous solutions. The study of these coordinated complexes provides further insight on the elucidation of structural aspects dealing with the nature of the S-N bond in RSNOs, a fact which still remains a matter of controversy.

Aberrant Insulin Receptor Signaling and Amino Acid Homeostasis as a Major Cause of Oxidative Stress in Aging

The mechanisms leading to the increase in free radical-derived oxidative stress in "normal aging" remains obscure. Here we present our perspective on studies from different fields that reveal a previously unnoticed vicious cycle of oxidative stress. The plasma cysteine concentrations during starvation in the night and early morning hours (the postabsorptive state) decreases with age. This decrease is associated with a decrease in tissue concentrations of the cysteine derivative and quantitatively important antioxidant glutathione. The decrease in cysteine reflects changes in the autophagic protein catabolism that normally ensures free amino acid homeostasis during starvation. Autophagy is negatively regulated by the insulin receptor signaling cascade that is enhanced by oxidative stress in the absence of insulin. This synopsis of seemingly unrelated processes reveals a novel mechanism of progressive oxidative stress in which decreasing antioxidant concentrations and increasing basal (postabsorptive) insulin receptor signaling activity compromise not only the autophagic protein catabolism but also the activity of FOXO transcription factors (i.e., two functions that were found to have an impact on lifespan in several animal models of aging). In addition, the aging-related decrease in glutathione levels is likely to facilitate certain "secondary" disease-related mechanisms of oxidative stress. Studies on cysteine supplementation show therapeutic promise.

ChemInform Abstract: Functionalization of Cysteine Derivatives by Unsymmetrical Disulfide Bond Formation.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Dynamics of the polymerase manager protein UmuD: DNA damage tolerance in E. coli

In E. coli, the function of specialized Y family DNA polymerases is regulated by UmuD, a small manager protein, and its cleaved form, UmuD′. The different forms of the UmuD proteins play dramatically different roles in the cellular response to DNA damage: UmuD facilitates a primitive DNA damage checkpoint while UmuD′ enables DNA damage‐dependent mutagenesis. The β processivity clamp, which tethers DNA polymerases to the DNA, confers high processivity on normal DNA polymerases. UmuD is known to bind the β clamp and this may modulate the activity of β. The objective of this study is to understand the conformational dynamics of UmuD to determine its effect on DNA damage tolerance. We constructed a library of single cysteine derivatives of UmuD to facilitate labeling for fluorescence resonance energy transfer (FRET) and electron paramagnetic resonance (EPR) studies. All single cysteine derivatives of UmuD were shown to be active in UV‐induced mutagenesis, and will be labeled. Hydrogen‐deuterium exchange mass spectrometry experiments show that UmuD is flexible, while UmuD′ is slightly less so.This work is supported by a Dreyfus Foundation New Faculty Award and the Northeastern University Office of the Provost.

A simple method for monitoring the cysteine content in synthetic peptides

A new method for the determination of the cysteine content of synthetic peptides is described. For this purpose the classical amino acid analysis is not suitable, as cysteine may undergo oxidative dimerisation to cystine during the hydrolysis or evaporation. The intact peptide was reacted with N-ethylmaleimide (NEM) yielding a stable S-(N-ethylsuccinimido)-cysteine derivative, which could be separated by RP-HPLC and characterised by mass spectrometry. For the quantitative determination less than 0.1 microM peptide was sufficient.

The Organophosphorus Sulfenyl Bromides as Versatile Reagents for Cysteine Derivatives Functionalization by Unsymmetrical Disulfide Bond Formation

We have developed a convenient method for the synthesis of L-cysteine unsymmetrical disulfides under mild conditions with good to excellent yields. Described method is based on the straightforward preparation of the organophosphorus sulfenyl bromide readily available from bis-(5,5-dimethyl-2-thiono-1,3,2-dioxaphosphorinanyl) disulfide. The unsymmetrical disulfides can be obtained for L-cysteine derivatives and thiols bearing neutral or acidic functionalities.

A viable synthesis of N-methyl cysteine.

While a number of methods exist for the production of N-methyl amino acid derivatives, the methods for the production of N-methyl cysteine (MeCys) derivatives are suboptimal as they either have low yields or lead to significant sulfhydryl deprotection during the synthetic protocol. This article focuses on the generation of MeCys and its subsequent use in Fmoc solid-phase peptide synthesis for the generation of N-methyl cystine containing peptides. Various methods for amino methylation of cysteine, in the presence of acid labile or acid stable sulfhydryl protecting groups, are compared and contrasted. Production of MeCys is best attained through formation of an oxazolidinone precursor obtained via cyclization of Fmoc--Cys(StBu)--OH. Following oxazolidinone ring opening, iminium ion reduction generates Fmoc--MeCys(StBu)--OH with an overall yield of 91%. The key to this procedure is using an electronically neutral Cys-derivative, as other polar Cys-derivatives gave poor results using the oxazolidinone procedure. Subsequently, the Fmoc--MeCys(StBu)--OH building block was used to replace a Cys residue with a MeCys residue in two peptide fragments that correspond to the active sites of glutaredoxin and thioredoxin reductase. The examples used here highlight the use of a MeCys(StBu) derivative, which allows for facile on-resin conversion to a MeCys(5-Npys) residue that can be subsequently used for intramolecular disulfide bond formation with concomitant cleavage of the peptide from the solid support. (c) 2007 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 90: 61-68, 2008. This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com.

酸・塩基複合塩を鍵とする高機能触媒の設計および高選択的合成法の開拓

The design of highly functionalized artificial catalysts is very important for practical organic synthesis. We have succeeded in the rational design of high-performance catalysts based on acid-base combined salts. Acid-base combined salt catalysts can be classified into three types: (1) Metal oxide-Lewis base combined salts, (2) Bronsted acid-Bronsted base combined salts, and (3) Lewis acid-Lewis base combined salts. Here we report our recent studies on development of highly selective cyclization reactions for the synthesis of key intermediates of bioactive natural products. Molybdenum(VI) oxide-bis(quinolinolato) complexes (class 1) efficiently catalyze biomimetic dehydrative cyclization of serine, threonine and cysteine derivatives to give oxazolines and thiazolines. Chiral 1, 1'-binaphthyl-2, 2'-diammonium salts (class 2) are useful catalysts for enantioselective Diels-Alder reaction of α-acyloxyacroleins. We also have developed the first enantioselective biomimetic iodocyclization of isoprenoids using a chiral nucleophilic promoter (class 3).

Hydrolytically and Reductively Degradable High‐Molecular‐Weight Poly(ethylene glycol)s

AbstractReductively degradable multiblock polymers for gene and drug delivery were synthesised by oxidative polycondensation of poly(ethylene glycol)‐cysteine derivatives containing ester or urethane bonds. Hydrolysis of the polymers at pH = 5.5, 7.4 and 8.0 and reductive degradation with glutathione and dithiothreitol were studied. The hydrolysis rate of polymer esters increased with increase in pH; the hydrolysis of polymer urethanes was negligible. Chemical substitution of the pendant COOH or NH2 groups significantly affected the rate of the polymer degradation. Surface modification of poly(L‐lysine)‐DNA complexes with PEG‐cystine multiblocks led to the formation of reductively degradable nanoparticles.magnified image

Functionalization of Cysteine Derivatives by Unsymmetrical Disulfide Bond Formation

We have developed a convenient method for the synthesis of unsymmetrical disulfides of l-cysteine under mild conditions in good to excellent yields. The described method is based on the straightforward preparation of 5,5-dimethyl-2-thioxo-1,3,2-dioxa­phosphorinane-2-sulfenyl bromide from readily available bis(5,5-dimethyl-2-thioxo-1,3,2-dioxaphosphorinan-2-yl) disulfide. The unsymmetrical disulfides can be obtained for l-cysteine derivatives and thiols bearing neutral, basic, or acidic functionalities.

The Application of199Hg NMR and199mHg Perturbed Angular Correlation (PAC) Spectroscopy to Define the Biological Chemistry of HgII: A Case Study with Designed Two- and Three-Stranded Coiled Coils

The use of de novo designed peptides is a powerful strategy to elucidate Hg(II)-protein interactions and to gain insight into the chemistry of Hg(II) in biological systems. Cysteine derivatives of the designed alpha-helical peptides of the TRI family [Ac-G-(L(a)K(b)A(c)L(d)E(e)E(f)K(g))(4)-G-NH(2)] bind Hg(II) at high pH values and at peptide/Hg(II) ratios of 3:1 with an unusual trigonal thiolate coordination mode. The resulting Hg(II) complexes are good water-soluble models for Hg(II) binding to the protein MerR. We have carried out a parallel study using (199)Hg NMR and (199m)Hg perturbed angular correlation (PAC) spectroscopy to characterize the distinct species that are generated under different pH conditions and peptide TRI L9C/Hg(II) ratios. These studies prove for the first time the formation of [Hg{(TRI L9C)(2)-(TRI L9C-H)}], a dithiolate-Hg(II) complex in the hydrophobic interior of the three-stranded coiled coil (TRI L9C)(3). (199)Hg NMR and (199m)Hg PAC data demonstrate that this dithiolate-Hg(II) complex is different from the dithiolate [Hg(TRI L9C)(2)], and that the presence of third alpha-helix, containing a protonated cysteine, breaks the symmetry of the coordination environment present in the complex [Hg(TRI L9C)(2)]. As the pH is raised, the deprotonation of this third cysteine generates the trigonal thiolate-Hg(II) complex Hg(TRI L9C)(3)(-) on a timescale that is slower than the NMR timescale (0.01-10 ms). The formation of the species [Hg{(TRI L9C)(2)(TRI L9C-H)}] is the result of a compromise between the high affinity of Hg(II) to form dithiolate complexes and the preference of the peptide to form a three-stranded coiled coil.