Cleavage of C-S Bond of Sulfolane Induced by Ultrasonically Dispersed Potassium

The reductive cleavage of the carbon-sulfur bond of sulfolane has been reinvestigated; a reaction mechanism is proposed.     

Carbon-sulfur bond cleavage reactions of dibenzothiophene derivatives mediated by iron and ruthenium carbonyls

A thermal reaction of 6-(4'-dibenzothienyl)-2,2'-bipyridine (bpyDBT) with [Ru(3)(CO)(12)] produced a sulfur-bridged triruthenium complex via double carbon-sulfur bond cleavage and CO insertion, while a diiron(I,I) complex containing a thiametallacycle was obtained by a photochemical reaction of bpyDBT with [Fe(CO)(5)].     

Site-specific radical directed dissociation of peptides at phosphorylated residues

Site-specific fragmentation of peptides at phosphorylated serine or threonine residues is demonstrated. This radical directed cleavage is accomplished by a two-step procedure. First the phosphate is replaced with naphthalenethiol using well established Michael Addition chemistry. Second, the modified peptide is electrosprayed and subjected to irradiation at 266 nm. Absorption at naphthalene causes homolytic cleavage of the connecting carbon-sulfur bond yielding a radical in the beta-position. Subsequent rearrangement cleaves the peptide backbone yielding a d-type fragment. This chemistry is generally applicable as demonstrated by experiments with several different peptides. Assignment of phosphorylation sites is greatly facilitated by this approach, particularly for peptides containing multiple serine or threonine residues.     

Vibration assignment of carbon-sulfur bond in 2-thione-1,3-dithiole-4,5-dithiolate derivatives

The higher frequency peak near 1050 cm(-1) of the doublet in the infrared and Raman spectra of 2-thione-1,3-dithiole-4,5-dithiolate (DMIT) derivatives corresponds mainly to the stretching vibration of carbon-sulfur double bond in the terminal S=CS2 fragments of DMIT skeletons while the lower one corresponds mainly to the Fermi resonance peak between overtones of symmetric stretching vibration of two carbon-sulfur single bond in the S=CS2 fragment of DMIT skeletons and the higher frequency. On the other hand, the higher frequency near 500 cm(-1) corresponds mainly to the symmetric stretching vibration of two carbon-sulfur single bond in the S=CS2 fragments of DMIT skeletons while the lower one corresponds mainly to the symmetric stretching vibration of the four carbon-sulfur single bond in the S2C=CS2 fragments of DMIT skeletons.     

Copper ion mediated selective cleavage of C-S bond in ferrocenylthiosemicarbazone forming mixed geometrical [(PPh3)Cu(μ-S)2Cu(PPh3)2] having Cu2S2 core: toward a new avenue in copper-sulfur chemistry

Unprecedented selective cleavage of the carbon-sulfur bond of the ferrocenylthiosemicarbazone moiety has been observed for the first time, resulting in the formation of mixed geometrical binuclear copper complex [(PPh(3))Cu(μ-S)(2)Cu(PPh(3))(2)]. Upon trying direct synthesis of the title complex, an unusual tetranuclear [Cu(4)(μ(3)-Cl)(4)(PPh(3))(4)] cubane resulted.     

On the mechanism of the copper-mediated C-S bond formation in the intramolecular disproportionation of imine disulfides

The mechanism of the copper-mediated disproportionation of aromatic imine disulfides to benzothiazoles in the gas phase is investigated by experimental and theoretical methods. Application of infrared multiphoton dissociation and hydrogen/deuterium exchange experiments combined with density functional theory (DFT) calculations of the relevant molecular structures and the associated infrared spectra allows the identification of the observed ionic intermediates. The theoretical investigation of the possible reaction pathways supported by collision-induced dissociation experiments provides a consistent mechanistic picture of the reaction catalyzed by a single copper(I) ion. Activation of the substrate proceeds via homolytic sulfur-sulfur bond cleavage, yielding metal complexes in the formal +3 oxidation state; carbon-sulfur coupling and hydrogen-atom transfer complete the transformation to the products. Exploratory studies demonstrate that in the gas phase, the disproportionation of the imine disulfide can also be mediated by other metal ions via different either homo- or heterolytic mechanisms without involving high-valent intermediates.     

Benzylic intermolecular carbon-carbon bond formation by selective anodic oxidation of dithioacetals

[reaction: see text]. Novel anodic intermolecular carbon-carbon bond formation has been accomplished by the oxidative carbon-sulfur bond fission of benzylic dithioacetals to give a wide variety of aromatic compounds. The substitution reaction successfully took place by the selective anodic oxidation of a sulfur atom of a dithioacetal. Stepwise double-substitution reactions were also achieved by the regulation of oxidation potential.     

Iron(0)-Mediated Stereoselective (3+2)-Cycloaddition of Thiochalcones via a Diradical Intermediate

Reactions of α,β-unsaturated aromatic thioketones 1 (thiochalcones) with Fe₃(CO)₁₂ leading to η⁴-1-thia-1,3-diene iron tricarbonyl complexes 2 , [FeFe] hydrogenase mimics 3 , and the thiopyrane adduct 4 are described. Obtained products have been characterized by X-ray crystallography and by computational methods. Completely regio- and diastereoselective formation of the five-membered ring system in products 3 , containing four stereogenic centers, can be explained by an unprecedented, stepwise (3+2)-cycloaddition of two thiochalcone molecules mediated by Fe₃(CO)₁₂. Quantum chemical calculations aimed at elucidation of the reaction mechanism, suggest that the formal (3+2)-cycloaddition proceeds via sequential intramolecular radical transfer events upon homolytic cleavage of one carbon-sulfur bond leading to a diradical intermediate.     

An efficient synthesis of a potent PPARpan agonist

An efficient synthesis of 2-{4-[({4-{[4-(4-methoxyphenyl)piperazin-1-yl]methyl}-2-[4-(trifluoromethyl)phenyl]-1,3-thiazol-5-yl}methyl)thio]phenoxy}-2-methylpropanoic acid (1), a potent PPARpan agonist, is described. The seven-step synthesis, which afforded 1 in 30% overall yield, includes a highly regioselective carbon-sulfur bond formation via coupling of a bishydroxymethylthiazole (3) with 4-hydroxythiophenol, displacement of the remaining alcohol through a three-step telescoped sequence involving an efficient cleavage of an aryl mesylate, and an efficient and practical method of introducing an isobutyric acid fragment.     

A general,efficient, and inexpensive catalyst system for the coupling of aryl iodides and thiols

An efficient copper-catalyzed carbon-sulfur bond formation reaction was developed. This method is particularly noteworthy given its experimental simplicity, high generality, and exceptional level of functional group toleration and the low cost of the catalyst system. [reaction: see text]     

基于2(5H)-呋喃酮的碳-杂成键反应研究进展

2(5H)-呋喃酮结构单元广泛存在于天然产物中,同时许多2(5H)-呋喃酮类化合物也是重要的有机合成中间体.因此,基于常见2(5H)-呋喃酮(1)的有机合成研究近年来引起了人们的关注.根据在有机合成反应中成键方式的不同,综述了在2(5H)-呋喃酮(1)环上形成C-O,C-N,C-S,C-P,C-Se,C-Si等碳-杂键的反应研究进展.     

Facile identification of photocleavable reactive metabolites and oxidative stress biomarkers in proteins via mass spectrometry

Described herein is a method which combines bond selective fragmentation by photodissociation with online liquid chromatographic separation and mass spectrometric analysis. Photoexcitation of proteins or peptides with 266-nm light does not normally yield abundant fragmentation; however, incorporation of a suitable carbon-sulfur or carbon-halogen bond that is proximal to a chromophore allows access to direct dissociation pathways, resulting in homolytic cleavage of these bonds. Radicals generated through this process can cause further dissociation of the peptide backbone, which is useful for site specifically identifying the point of modification. Two specific applications of this technique for peptide analysis in model systems are presented: (1) identification of reactive metabolites which covalently modify cysteine residues, and (2) characterization of halogenated tyrosine residues which are biomarkers related to oxidative stress. In both cases, these naturally occurring post translational modifications create photocleavable bonds which can be fragmented by 266-nm light. The selectivity offered by photodissociation allows facile identification of the peptides of interest even in complex mixtures, and subsequent selective radical directed backbone fragmentation pinpoints the site of modification. This combination greatly simplifies data analysis and provides more confident assignments.     

KINETICS AND MECHANISM FOR INTRAMOLECULAR ISOMERIZATION OF HRu3 (μ3-η3-EtSCCMeCMe)(CO)9 TO Ru3(μ-SEt) (μ3-η3-CCMeCHMe)(CO)9

Abstract

The kinetics for isomerization of HRu₃ (μ₃-η³-EtSCCMeCMe)(CO)₉ TO Ru₃(μ-SEt) (μ₃-η³-CCMeCHMe)(CO)₉, were determined. The overall process involves C[sbnd]H elimination, C[sbnd]S and Ru[sbnd]Ru bond cleavage and Ru₂(μ-S) bond formation. Activation parameters were determined from the temperature dependence (ΔH^? = 127(3) kJ/mol, ΔS^?= 56(11) J/mol-K) and from the pressure dependence (0[sbnd]207 MPa, ΔV^? ₀ +12.7(1.1) cm³/mol, Δβ^? = +0.037(0.012) cm³/(mol-MPa)) of the rate constant. The data are consistent with an intramolecular reaction involving significant metal-metal or carbon-sulfur bond cleavage in the transition state. The activation volume is too large to be accommodated by C[sbnd]H elimination alone and CO dissociation is not involved.     

Electrospray low energy CID and MALDI PSD fragmentations of protonated sulfinamide cross-linked peptides

Murine S100A8 (A8) is a major cytoplasmic neutrophil protein and is converted to novel oxidation products containing Cys-epsilon amino-Lys sulfinamide cross-links and Met-sulfoxide by the neutrophil oxidant HOCl. Seven products were separated using RP-HPLC, with electrospray ionization mass spectrometry (ESI-MS) masses after deconvolution of 10,354, 10,388, +/- 1, and 20,707, +/- 3 Da, and all were resistant to reduction by dithiothreitol. The major products with masses of 10,354 Da contained Cys41-Lys34/35 intramolecular cross-links. Additional isomeric products with identical masses (10,354 Da) were isolated and peptide mapping and ESI/MS indicated that Cys41 forms covalent sulfinamide cross-links with either Lys6, Lys76, Lys83, or Lys87 present in A8. Electrospray low energy collisionally induced (CID) spectra of multiply-charged AspN digest peptides with sulfinamide cross-links contained characteristic fragmentations that corresponded to simple cleavage of the nitrogen-sulfur bond with charge retention on either of the fragment ions, allowing conformation of cross-linked peptides. Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) post source decay spectra of [M + H] + ions of the same sulfinamide-containing cross-linked peptides fragment similarly, but additional facile fragmentation reactions corresponding to formation of a protonated peptide containing de-hydroalanine were attributed to cleavage of the carbon-sulfur bond. In addition, lose of methanesulfenic acid from Met-sulfoxide was observed. A sulfinamide-containing adduct was isolated after incubation of the A8/HOCl reaction mixture with Lys or alpha N-acetyl Lys with masses of 10,500 or 10,542 Da. ESI/MS/MS and MALDI/post decay source (PSD) analysis of A8(32)-(57)-sulfinamide showed the same characteristic fragmentations as those in the sulfinamide cross-linked peptides, confirming the Cys41-Lys sulfinamide cross-link and suggesting that peptide-peptide sulfinamides may all fragment similarly, allowing ready identification of these cross-links in proteins from more complex biological materials.     

New Perspectives in Thiazole Chemistry

Abstract

Carbon-carbon bond forming reactions at C-2 of the thiazole ring have been carried using two strategies, one involving the addition of organometallic reagents (lithium carbanions of esters, Grignard salts, silyl enol ethers, silyl ketene acetals, silylazoles) to N-acylthiazolium salts; the other involving the addition of carbon electrophiles (ketenes, acyl chlorides, anhydrides, aldehydes) to N-acylthiazolium ylides generated in situ. The reactions have been applied to 1,3-thiazole and 2-trimethylsilyl-1,3-thiazole, the latter being more reactive than the former toward electrophiles. This methodology constitutes a new entry to a variety of functionalized thiazoles and thiazolines which are potential building blocks for the synthesis of natural compounds and analogues of biologically active molecules (penems, arylpropionic acids). Some ring transformations of thiazoles induced by carbon-sulfur bond cleavage are also described. The fundamental role played by the sulfur atom of the thiazole ring in the observed reactions is pointed out and briefly discussed.     

Identification of photoproducts from imazosulfuron by HPLC

Photolysis of imazosulfuron was studied in aqueous solution under UV light. The reaction followed a pseudo-first-order kinetic with significant correlation coefficient. The major photodegradation products of imazosulfuron after irradiation under UV light were separated and tentatively identified by HPLC-MS analysis as (4,6-dimethoxypyrimidine-2-yl)aminocarbonylsulfamic acid, 4,6-dimethoxy-2-ureidopyrimidine and 2,2'-dichloro-[3,3'] bi [imidazo[1,2-a] pyridinyl]. The results indicate that different reaction pathways are followed: (1) cleavage of the sulfonylurea bridge; (2) desulfonylation, which can proceed either by a carbon-sulfur cleavage or a nitrogen-sulfur cleavage. A mechanism for the formation of the photoproducts is proposed.     

Photochemistry of diethynyl sulfides: a cycloaromatization for the formation of five-membered rings

The first five-membered ring cycloaromatization reaction has been demonstrated. Photoirradiation of bis(phenylethynyl) sulfide in hexanes/1,4-cyclohexadiene produces 3,4-diphenylthiophene through the presumed intermediacy of 2,5-didehydrothiophene. In addition, phenylacetylene is produced in this reaction consistent with competing direct carbon-sulfur cleavage. For reactions in ethanol or 2-propanol production of the thiophene is accompanied by the formation of phenylacetylene and a thionoester of the corresponding alcohol. Thiophene products also result from the irradiation of other diethynyl sulfides. [reaction: see text]     

Efficient synthesis of 1,3,5-trisubstituted benzenes via three Pd-mediated carbon-sulfur, carbon-nitrogen and carbon-carbon bond formation reactions

An efficient synthesis of 1,3,5-trisubstituted benzenes via a sequential Pd-mediated carbon-sulfur, carbon-nitrogen, and carbon-carbon bond formation reactions is reported. Selective amidation and sulfonamidation reactions are accomplished via Pd-catalyzed reactions between aryl chlorides and an acetamide or a methanesulfonamide.     

NMR approach for the identification of dinuclear and mononuclear complexes: The first detection of [Pd(SPh)2(PPh3)2] and [Pd2(SPh)4(PPh3)2] - The intermediate complexes in the catalytic carbon-sulfur bond formation reaction

In the present study we have analyzed the nature of palladium complexes in the catalytic system for selective carbon-sulfur bond formation via the addition of S-S and S-H bonds to alkynes. For the first time the mononuclear and dinuclear palladium complexes were clearly detected by DOSY NMR under the catalytic conditions. It was demonstrated that the concentration of these palladium complexes strongly depends on the amount of phosphine ligand available under reaction conditions.     

On the origin of cytotoxicity of the natural product varacin. A novel example of a pentathiepin reaction that provides evidence for a triatomic sulfur intermediate

A density functional theoretical study is presented, which implicates a novel S(3)-cleavage in the decomposition of a pentathiepin. This study predicts an interconversion between a pentathiepin and an open-chain polysulfur ion intermediate from which a key determinant in the chemistry then follows. Expulsion of diatomic sulfur, S(2), is unlikely from the unimolecular collapse of the open-chain polysulfur ion. Instead, S(3) can dissociate due to an unusually long and weak sulfur-sulfur (S4-S5) bond. A mechanistic picture now emerges which predicts that the novel S-S cleavage reaction and the unanticipated S(3) fragmentation are a result of delocalization of the negative charge within the remaining carbon-sulfur fragment. The computed results presented here reveal a new aspect to the chemistry of pentathiepins, that of S(3) unit transfer, which is proposed to have significance in the mechanism of cytotoxicity of the natural product varacin, 1.