Selenocysteine Derivatives Research Articles

Strategies for the Synthesis of Selenocysteine Derivatives

Abstractβ-Seleno-α-amino acids, known as selenocysteine (Sec) derivatives, have emerged as important targets because of their role in chemical biology, not only as part of selenoproteins with important redox properties, but also because of their activity as antivirals or metabolites effective in inhibiting carcinogenesis. In addition, there is demand for this type of compounds due to their use in native chemical ligation to construct large peptides. Therefore, this review summarizes the various synthetic methods that have been published to construct Sec derivatives. Most of them involve the generation of the C–Se bond by nucleophilic substitution reactions, but other reactions such as radical or multicomponent strategies are also reported. Of particular importance is the Se-Michael addition of Se-nucleophiles to chiral bicyclic dehydroalanines, in which the stereogenic center is generated under complete stereocontrol.1 Introduction2 Previously Reviewed Synthesis of Sec3 Retrosynthesis of Sec Derivatives4 Sec Derivatives by Nucleophilic Substitutions5 Sec Derivatives by Radical Processes6 Sec Derivatives by 1,4-Conjugate Additions7 Conclusion

Toward Enantiomerically Pure β-Seleno-α-amino Acids via Stereoselective Se-Michael Additions to Chiral Dehydroalanines.

The first totally chemo- and diastereoselective 1,4-conjugate additions of Se-nucleophiles to a chiral bicyclic dehydroalanine (Dha) are described. The methodology is simple and does not require any catalyst, providing exceptional yields at room temperature, and involves the treatment of the corresponding diselenide compound with NaBH4 in the presence of the Dha. These Se-Michael additions provide an excellent channel for the synthesis of enantiomerically pure selenocysteine (Sec) derivatives, which pose high potential for chemical biology applications.

Copper-Mediated Deprotection of Thiazolidine and Selenazolidine Derivatives Applied to Native Chemical Ligation.

Cupric sulfate efficiently opens thiazolidine and selenazolidine rings, producing a protected N-terminal cysteine or selenocysteine derivative without the use of inert gas or solvent. This is a clear advantage over methods that use water-soluble palladium salts, which fail to react with the selenazolidine ring. This copper-mediated reaction proceeds with monovalent or divalent copper ions, and disulfide bond formation followed by ring-opening promotes the process. This copper-mediated reaction, which is compatible with the standard native chemical ligation conditions, was applied to the synthesis of the 77-mer CXCL14 protein.

A TP-FRET-based fluorescent sensor for ratiometric visualization of selenocysteine derivatives in living cells, tissues and zebrafish

Selenium is a biologically essential micronutrient element serving as an essential building block for selenoproteins (SePs), which is playing a key role in various cellular functions. Hence, it is of great significance to developing a reliable and rapid method for detection of Sec in biosystems. Compared with the previously reported probes that have been developed for selective detection of Sec, two-photon (TP) ratiometric Sec-specific probes would be advantageous for the NIR excitation and built-in correction of the dual emission bands. To quantitatively and selectively detect Sec over biothiols with rapid and sensitive response, we for the first time report a new fluorescence resonance energy transfer (FRET)-based TP ratiometric fluorescence probe CmNp-Sec, which was constructed by conjugating a TP fluorophore 6 (coumarin derivative with a D-π-A-structure) with a naphthalimide fluorophore 9 via a non-conjugated linker, and employed a 4-dinitrobenzene-ether (DNB) with a strong ICT effect as Sec responsive moiety. It exhibits quantitatively detect Sec in a wide range (0-50 μM) with a limit of detection of 7.88 nM within 10 min. More impressively, this probe can be conveniently used to detect Sec in living cells, tissues and zebrafish, demonstrating it has the latent capability in further biological applications.

Modelling the Inhibition of Selenoproteins by Small Molecules Using Cysteine and Selenocysteine Derivatives.

Small molecule-based electrophilic compounds such as 1-chloro-2,4-dinitrobenzene (CDNB) and 1-chloro-4-nitrobenzene (CNB) are currently being used as inhibitors of cysteine- and selenocysteine-containing proteins. CDNB has been used extensively to determine the activity of glutathione S-transferase and to deplete glutathione (GSH) in mammalian cells. Also, CDNB has been shown to irreversibly inhibit thioredoxin reductase (TrxR), a selenoenzyme that catalyses the reduction of thioredoxin (Trx). Mammalian TrxR has a C-terminal active site motif, Gly-Cys-Sec-Gly, and both the cysteine and selenocysteine residues could be the targets of the electrophilic reagents. In this paper we report on the stability of a series of cysteine and selenocysteine derivatives that can be considered as models for the selenoenzyme-inhibitor complexes. We show that these derivatives react with H2 O2 to generate the corresponding selenoxides, which undergo spontaneous elimination to produce dehydroalanine. In contrast, the cysteine derivatives are stable towards such elimination reactions. We also demonstrate, for the first time, that the arylselenium species eliminated from the selenocysteine derivatives exhibit significant redox activity by catalysing the reduction of H2 O2 in the presence of GSH (GPx (glutathione peroxidase)-like activity), which suggests that such redox modulatory activity of selenium compounds may have a significant effect on the cellular redox state during the inhibition of selenoproteins.

Nutritionally Available Selenocysteine Derivative Antagonizes Cisplatin-Induced Toxicity in Renal Epithelial Cells through Inhibition of Reactive Oxygen Species-Mediated Signaling Pathways.

Discovery of nutritionally available agents that could antagonize cisplatin-induced nephrotoxicity is of great significance and clinical application potential. 3,3'-Diselenodipropionic acid (DSePA) is a seleno-amino acid derivative that exhibits strong antioxidant activity. Therefore, this study aimed to examine the protective effects of DSePA on cisplatin-induced renal epithelial cells damage as well as the molecular mechanisms. The results revealed that DSePA effectively inhibited cell apoptosis induced by cisplatin through suppressing the caspase activation and poly(ADP-ribose) polymerase cleavage. In addition, DSePA blocked the cisplatin-induced mitochondrial dysfunction, as evidenced by the loss of mitochondrial membrane potential and reduction of mitochondrial mass. The results of western blot analysis showed that DSePA reversed the expression level of Bcl-2 family proteins altered by cisplatin. The cisplatin-activated AKT pathway was also modulated by DSePA. Moreover, these results indicate that DSePA could protect HK-2 cells from cisplatin-induced toxicity in renal epithelial cells by inhibiting intracellular reactive oxygen species-mediated apoptosis while showing an unobvious effect on its anticancer efficacy. Taken together, this study demonstrates that selenocysteine could be further developed as novel nutritionally available agents to antagonize cisplatin-induced nephrotoxicity during cancer therapy.

Improved synthetic routes to the selenocysteine derivatives useful for Boc-based peptide synthesis with benzylic protection on the selenium atom

Improved synthetic routes to the selenocysteine derivatives useful for Boc-based peptide synthesis with benzylic protection on the selenium atom

Selenocysteine derivative overcomes TRAIL resistance in melanoma cells: evidence for ROS-dependent synergism and signaling crosstalk.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), as one of the most promising targeted drug for new cancer therapeutics, is limited in clinical application by the evolution of resistance in many cancer cell lines, especially in malignant melanoma. Thus, it is urgently needed to identify chemosensitizers to enhance the apoptotic inducing efficacy of TRAIL and overcome resistance of malignant melanoma cells. Herein, we reported that 3,3'-diselenodipropionic acid (DSeA), a Selenocysteine derivative, could synergistically enhance the growth inhibitory effect of TRAIL on A375 melanoma cells though induction of ROS-dependent apoptosis with involvement of PTEN-mediated Akt inactivation and DNA damage-mediated p53 phosphorylation, which subsequently activated mitochondrial and death receptor apoptotic pathways. Moreover, silencing of p53 down-regulated the expression levels of p53-inducible genes, and effectively blocked the cell apoptosis. Suppression of PI3K significantly increased the apoptotic cell death. In contrast, antioxidants effectively reversed the cell apoptosis through regulation of Akt and p53 signaling pathways. Taken together, the combination of DSeA and TRAIL could be a novel strategy to overcome TRAIL resistance in malignant melanoma, and DSeA may be candidates for further evaluation as a chemosensitizer in clinical trails.

A Selenocysteine Derivative Therapy Affects Radiation-Induced Pneumonitis in the Mouse

The mechanism leading to the radiation-induced lung response of pneumonitis is largely unknown. Here we investigated whether treatment with 3,3'-diselenodipropionic acid (DSePA), which reduces radiation-induced oxidative stress in acute response models, decreases the lung response to irradiation. Mice of the C3H/HeJ (alveolitis/pneumonitis-responding) strain received 18 Gy whole-thorax irradiation, and a subset of these mice was treated with DSePA (2 mg/kg) three times per week, beginning at 2 hours after radiation treatment, and continuing in the postirradiation period until death because of respiratory distress symptoms. DSePA treatment increased the postirradiation survival time of mice by an average of 32 days (P = 0.0002). Radiation-treated and DSePA-treated mice presented lower levels of lipid peroxidation and augmented glutathione peroxidase in the lungs, compared with those levels measured in mice receiving radiation only, when mice receiving radiation only were killed because of distress symptoms, whereas catalase and superoxide dismutase levels did not show consistent differences among treatment groups. DSePA treatment decreased pneumonitis and the numbers of mast cells, neutrophils, and lymphocytes in the lungs and bronchoalveolar lavage, respectively, of irradiated mice relative to mice exposed to radiation alone. DSePA treatment also decreased the radiation-induced increase in granulocyte colony-stimulating factor levels in the bronchoalveolar lavage and lung-tissue expression of intercellular adhesion molecule-1 and E-selectin, while increasing the expression of glutathione peroxidase-4. We conclude that DSePA treatment reduces radiation-induced pneumonitis in mice by delaying oxidative damage and the inflammatory cell influx.

The use of 2,2′‐dithiobis(5‐nitropyridine) (DTNP) for deprotection and diselenide formation in protected selenocysteine‐containing peptides

In contrast to the large number of sidechain protecting groups available for cysteine derivatives in solid phase peptide synthesis, there is a striking paucity of analogous selenocysteine Se-protecting groups in the literature. However, the growing interest in selenocysteine-containing peptides and proteins requires a corresponding increase in availability of synthetic routes into these target molecules. It therefore becomes important to design new sidechain protection strategies for selenocysteine as well as multiple and novel deprotection chemistry for their removal. In this paper, we outline the synthesis of two new Fmoc selenocysteine derivatives [Fmoc-Sec(Meb) and Fmoc-Sec(Bzl)] to accompany the commercially available Fmoc-Sec(Mob) derivative and incorporate them into two model peptides. Sec-deprotection assays were carried out on these peptides using 2,2'-dithiobis(5-nitropyridine) (DTNP) conditions previously described by our group. The deprotective methodology was further evaluated as to its suitability towards mediating concurrent diselenide formation in oxytocin-templated target peptides. Sec(Mob) and Sec(Meb) were found to be extremely labile to the DTNP conditions whether in the presence or absence of thioanisole, whereas Sec(Bzl) was robust to DTNP in the absence of thioanisole but quite labile in its presence. In multiple Sec-containing model peptides, it was shown that bis-Sec(Mob)-containing systems spontaneously cyclize to the diselenide using 1 eq DTNP, whereas bis-Sec(Meb) and Sec(Bzl) models required additional manipulation to induce cyclization.

One-Pot Conversion of Serine and α-Methylserine Derivatives to the Corresponding Cysteines and Selenocystines by Using Chalcogenophosphate Reagents

The one-pot reactions of N-acetylserine methyl ester and N-acetyl-α-methylserine methyl ester with Lawesson's or Woollins’ reagent directly produced the corresponding cysteine or selenocysteine derivatives in moderate yields. The transformation would be initiated by phosphorylation of the hydroxy group, rather than chalcogenation of the amide group, and involve the oxazoline as a key intermediate. Supplemental materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file. GRAPHICAL ABSTRACT

Selenocysteine Positional Variants Reveal Contributions to Copper Binding from Cysteine Residues in Domains 2 and 3 of Human Copper Chaperone for Superoxide Dismutase

The human copper chaperone for superoxide dismutase binds copper both in an Atx1-like MTCQSC motif in domain 1 and via a multinuclear cluster formed by two CXC motifs at the D3 dimer interface. The composition of the Cu(I) cluster has been investigated previously by mutagenesis of the CXC motif, and by construction of a CXU selenocysteine derivative, which has permitted XAS studies at both Cu and Se absorption edges. Here, we report the semisynthesis and spectroscopic characterization of a series of derivatives with the sequences 243-CACA, 243-CAUA, 243-UACA, and 243-UAUA in the D1 double mutant (C22AC25A) background, prepared by expressed protein ligation of Sec-containing tetrapeptides to an hCCS-243 truncation. By varying the position of the Se atom in the CXC motif, we have been able to show that Se is always bridging (2 Se-Cu) rather than terminal (1 Se-Cu). Substitution of both D3 Cys residues by Sec in the UAUA variant does not eliminate the Cu-S contribution, confirming our previous description of the cluster as most likely a Cu(4)S(6) species, and suggesting that D2 Cys residues contribute to the cluster. As predicted by this model, when Cys residues C141, C144, and C227 are mutated to alanine either individually or together as a triple mutant, the cluster nuclearity is dramatically attenuated. These data suggest that Cys residues in D2 of hCCS are involved in the formation, stability, and redox potential of the D3 cluster. The significance of these finding to the SOD1 thiol/disulfide oxidase activity are discussed in terms of a model in which a similar multinuclear cluster may form in the CCS-SOD heterodimer.

Bioactivation of Selenocysteine Derivatiives by β-Lyases Present in Common Gastrointestinal Bacterial Species

Studies in cell cultures and animal models have demonstrated cancer chemopreventive effects of certain selenium compounds. Here we describe the screening of cysteine S-conjugate beta-lyase activity in bacterial species that are implicated in the bio-activation of sulfur- and selenocysteine derivatives. We screened a range of bacterial species commonly found in the human intestine for beta-lyase activity on Se-p-methoxybenzylselenocysteine and the natural occurring S-methylcysteine and Se-methylselenocysteine conjugates. A high-performance liquid chromatography (HPLC)-assisted assay was established to determine specific activities of each strain. Of the 29 tested bacterial species, 22 showed specific activities towards the test compound reaching up to 10.1 U/mg protein, thereby accounting for 75% of total fecal activity (13.3. U/mg protein). Lysates of four bacterial strains (Bacteroides distasonis, bacteroides vulgatus, Enterococcus faecalis, and Enterococcus faecium), which exhibited high specific activities towards the test compound and which are known to be present at high numbers in the human intestine, were characterized further. Our results indicate that beta-lyase activity is widely distributed in human intestinal bacteria and might play a key role in the bioactivation of selenocysteine derivatives.

A Selenocysteine Variant of the Human Copper Chaperone for Superoxide Dismutase. A Se-XAS Probe of Cluster Composition at the Domain 3−Domain 3 Dimer Interface

We report the semisynthesis of a selenocysteine (Sec) derivative of the human copper chaperone for superoxide dismutase, substituted with Sec at the C-terminal C246 residue. Measurements of hCCS-induced SOD1 activation were used to show that the C-terminal CXC sequence is both necessary and sufficient for EZn-SOD maturation. Therefore, an active CAU variant carrying Sec as the terminal amino acid was prepared by expressed protein ligation of a single selenocysteine amino acid to a 243-CA truncation. This reaction proceeded in high yield and generated the desired 243-CAX (X = C or U) protein with the expected mass. Se-edge XAS of the apoprotein indicated that both Se-S and Se-Se interactions were present in a 0.3:0.7 ratio, indicating an equilibrium between species with either a selenosulfide or a diselenide cross-link. After reduction on immobilized TCEP, the ligated Cys and Sec apoproteins bound up to 2.5 Cu(I) ions per hCCS monomer with both Cu and Se as constituent atoms of the cluster which forms at the domain 3 interface of a hCCS dimer. Merging of XAS data at the Cu and Se K-absorption edges provided additional details of the cluster composition, specifically the fact that both Se atoms occupied bridging positions between two Cu(I) atoms. Further, the requirement for identical Cu-Se bond lengths and Debye-Waller factors at each absorption edge allowed us to rule out simple models for the cluster composition such as a bis-Cys(Sec)-bridged dinuclear cluster and was indicative of a more complex cluster with a nuclearity of >or=3.

ChemInform Abstract: One‐Pot Indium Iodide Mediated Synthesis of Chiral β‐Seleno Amides and Selenocysteine Derivatives by Ring‐Opening Reaction of 2‐Oxazolines.

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.

One‐Pot Indium Iodide Mediated Synthesis of Chiral β‐Seleno Amides and Selenocysteine Derivatives by Ring‐Opening Reaction of 2‐Oxazolines

AbstractA set of chiral β‐seleno amides were efficiently synthesized by a simple and efficient procedure involving a ring‐opening reaction of 2‐oxazoline with diorganyl dichalcogenides mediated by indium(I) iodide. As an application, the synthesis of selenocysteine derivatives was accomplished. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Chiral Seleno‐Amines from Indium Selenolates. A Straightforward Synthesis of Selenocysteine Derivatives.

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, please click on HTML or PDF.

Activation energies of selenoxide elimination from Se-substituted selenocysteine

Transition states for selenoxide elimination have been determined for a series of Se-substituted selenocysteine (RSeCys) derivatives that have potential use in the prevention and treatment of cancer, either directly or in conjunction with cisplatin (to reduce its nephrotoxic effects). Reduced activation barriers vs R=Me and R=Ph are found when the alkyl chain length is increased or when activating groups are para to the selenide. Ortho substitution of Lewis bases stabilizes the transition state by directly donating electron density to the selenoxide. The results suggest that RSeCys derivatives incorporating the properties of glutathione peroxidase mimics will, upon oxidation, rapidly eliminate selenenic acid, a precursor to chemopreventative selenols.

Chiral Seleno-Amines from Indium Selenolates. A Straightforward Synthesis of Selenocysteine Derivatives

A simple and efficient procedure for the synthesis of chiral beta-seleno-amines derivatives from a one-pot indium(I) iodide-mediated aziridine ring opening with diorganoyl diselenides has been developed. As an application, the synthesis of selenocysteine and selenotreonine derivatives has been accomplished.

Efficient Synthesis of Chiral β-Seleno Amides via Ring-Opening Reaction of 2-Oxazolines and Their Application in the Palladium-Catalyzed Asymmetric Allylic Alkylation

[structure: see text] A set of chiral beta-seleno amides have been efficiently synthesized via the ring-opening reaction of chiral 2-oxazolines by selenium nucleophiles. The present method is applicable to the synthesis of beta-seleno amides containing thioether, alcohol, and ether moieties in good yields. As an application, the synthesis of a selenocysteine derivative has been accomplished. Additionally, these new compounds were evaluated in the palladium-catalyzed asymmetric allylic alkylation, giving the alkylated products in up to 98% ee.