thiourea and formic-acid

A time economical 60 min total synthesis of (-)-oseltamivir was accomplished in a single reaction vessel over five steps. One of the key issues is reduction in the number of steps by eliminating lengthy reaction steps with substitution of a rapid epimerization step. A catalytic system consisting of three reagents, namely, diphenylprolinol silyl ether, thiourea, and acid, was developed for a rapid asymmetric Michael reaction with excellent diastereo- and enantioselectivities. All reactions were optimized in terms of not only yield and selectivity but also reaction time.

Topics: Antiviral Agents; Catalysis; Efficiency; Ethers; Formates; Oseltamivir; Proline; Stereoisomerism; Thiourea

Protein or peptide sample losses could accompany all steps of the proteomic analysis workflow. We focused on suppression of sample adsorptive losses during sample storage in autosampler vials. We examined suppression capabilities of six different sample injection solutions and seven types of autosampler vial surfaces using a model sample (tryptic digest of six proteins, 1 fmol per protein). While the vial material did not play an essential role, the choice of appropriate composition of sample injection solution reduced adsorptive losses substantially. The combination of a polypropylene vial and solution of poly(ethylene glycol) (PEG) (0.001%) or a mixture of high concentrated urea and thiourea (6 M and 1 M) as injection solutions (both acidified with formic acid (FA) (0.1%)) provided the best results in terms of number of significantly identified peptides (p < 0.05). These conclusions were confirmed by analyses of a real sample with intermediate complexity (in-gel digest from sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE)). Addition of PEG into the real sample solution proved to prevent higher losses, concerning mainly hydrophobic peptides, during up to 48 h storage in the autosampler in comparison with a formic acid solution and even with a solution of highly concentrated urea and thiourea. Using PEG for several months was not accompanied by any adverse effect to the liquid chromatography system.

Topics: Adsorption; Chromatography, Liquid; Electrophoresis, Polyacrylamide Gel; Flow Injection Analysis; Formates; Hydrophobic and Hydrophilic Interactions; Peptide Fragments; Polyethylene Glycols; Proteins; Specimen Handling; Thiourea; Urea

A range of 3H-indoles and 2H-benzo[b][1,4]thiazines smoothly undergo asymmetric Strecker reaction with ethyl cyanoformate in the presence of a Cinchona alkaloid-based thiourea catalyst at 10 °C to give structurally diverse nitrogen-containing heterocycles in good to excellent yields and with excellent ee.

Topics: Catalysis; Cinchona; Cinchona Alkaloids; Formates; Imines; Stereoisomerism; Thiazines; Thiourea

Cultured vascular smooth muscle cells (SMC) and endothelial cells (EC) stimulate low density lipoprotein (LDL) oxidation by free radical-mediated, transition metal-dependent mechanisms. The physiological source(s) of metal ions is not known; however, purified ceruloplasmin, a plasma protein containing 7 coppers, oxidizes LDL in vitro. We now show that ceruloplasmin also increases LDL oxidation by vascular cells. In metal ion-free medium, human ceruloplasmin increased bovine aortic SMC- and EC-mediated LDL oxidation by up to 30- and 15-fold, respectively. The maximal response was at 100-300 microg ceruloplasmin/ml, a level at or below the unevoked physiological plasma concentration. Oxidant activity was dependent on protein structure as a specific proteolytic cleavage or removal of one of the seven ceruloplasmin copper atoms inhibited activity. Three lines of evidence indicated a critical role for cellular superoxide (O2.) in ceruloplasmin-stimulated oxidation. First, the rate of production of O2. by cells correlated with their rates of LDL oxidation. Second, superoxide dismutase effectively blocked ceruloplasmin-stimulated oxidation by both cell types. Finally, O2. production by SMC quantitatively accounted for the observed rate of LDL oxidation. To show this, the course of O2. production by SMC was simulated by repeated addition of xanthine and xanthine oxidase to culture medium under cell-free conditions. Neither ceruloplasmin nor O2. alone increased LDL oxidation, but together they completely reconstituted the oxidation rate of ceruloplasmin-stimulated SMC. These results are the first to show that ceruloplasmin stimulates EC- and SMC-mediated oxidation of LDL and that cell-derived O2. accounts quantitatively for metal-dependent, free radical-initiated oxidation of LDL by these cells.

Topics: Animals; Aorta; Catalase; Cattle; Cells, Cultured; Ceruloplasmin; Dose-Response Relationship, Drug; Endothelium, Vascular; Formates; Free Radical Scavengers; Glutathione; Humans; Kinetics; Lipoproteins, LDL; Mannitol; Muscle, Smooth, Vascular; Oxidation-Reduction; Superoxide Dismutase; Superoxides; Thiourea

An iron chelate, ferric ethylenediamine-N,N'-diacetate [Fe(III)-EDDA], was found to produce hydroxyl radicals with hydrogen peroxide, as determined by both a deoxyribose degradation test and electron spin resonance. Hydroxyl radical production was inhibited not only by adding hydroxyl radical scavengers and catalase, but also by adding superoxide dismutase to the reaction mixture, suggesting that superoxide anion may be involved in the hydroxyl radical production. A single injection of Fe(III)-EDDA (10 mg Fe/kg body wt) to Wistar rats induced thiobarbituric acid reactivity in the kidneys and liver. Repeated injections of Fe(III)-EDDA (10 mg Fe/kg body wt, twice weekly for 3 months) induced a 40% incidence of renal tumors, including renal adenocarcinoma and renal adenoma, 1 year later. These results suggest that Fe(III)-EDDA is an effective free radical producer in vitro and in vivo and that it may be useful in preparing animal models related to iron-dependent free radical damage. The results support our hypothesis that endogenous or exogenous iron, complexed with certain kinds of chelators, promotes free radical-dependent tissue damage and ultimately leads to carcinogenesis in the affected tissue.

Topics: Adenocarcinoma; Adenoma; Animals; Catalase; Cell Transformation, Neoplastic; Deoxyribose; Edetic Acid; Ferric Compounds; Formates; Hydrogen Peroxide; Hydroxyl Radical; Kidney; Kidney Neoplasms; Lipid Peroxidation; Male; Mannitol; Nitrilotriacetic Acid; Rats; Rats, Wistar; Reactive Oxygen Species; Superoxide Dismutase; Superoxides; Thiobarbituric Acid Reactive Substances; Thiourea

Cu-catalyzed oxidation of ascorbate has been studied in the absence and the presence of superoxide dismutase, catalase, mannitol, glycerol, ethanol, formate, and thiourea. None of these agents except thiourea inhibited the reaction. Therefore, the role of the Haber-Weiss reaction in the ascorbate oxidation could not be demonstrated. Electron spin resonance studies demonstrated that the preventive effect of the thiol is primarily due to the chelation of the reduced copper ions with the sulphur atom. The oxidation was also prevented by the chelation of copper with physiological levels of bovine serum albumin. These observations are consistent with the concept that a metal-oxygen complex is perhaps directly involved in the oxidative process. Measurements of the peroxide produced during oxidation indicated that significant amounts of this compound accumulates only at lower levels of ascorbate and in the absence of a protein or other chelating agents. At higher ascorbate levels no peroxide accumulation takes place. These results are, thus, useful in predicting the conditions under which the nutrient may act as a pro-oxidant or as an anti-oxidant. The observations suggest that under normal conditions low levels of ascorbate may act as a pro-oxidant through H2O2 production if the system has transition metal ions devoid of chelating agents. At higher concentrations ascorbate acts predominantly as an antioxidant.

Topics: Ascorbic Acid; Catalase; Catalysis; Copper; Electron Spin Resonance Spectroscopy; Formates; Glycerol; Hydrogen Peroxide; Mannitol; Oxidation-Reduction; Superoxide Dismutase; Thiourea

Hydroxyl radicals (OH.) in free solution react with scavengers at rates predictable from their known second-order rate constants. However, when OH. radicals are produced in biological systems by metal-ion-dependent Fenton-type reactions scavengers do not always appear to conform to these established rate constants. The detector molecules deoxyribose and benzoate were used to study damage by OH. involving a hydrogen-abstraction reaction and an aromatic hydroxylation. In the presence of EDTA the rate constant for the reaction of scavengers with OH. was generally higher than in the absence of EDTA. This radiomimetic effect of EDTA can be explained by the removal of iron from the detector molecule, where it brings about a site-specific reaction, by EDTA allowing more OH. radicals to escape into free solution to react with added scavengers. The deoxyribose assay, although chemically complex, in the presence of EDTA appears to give a simple and cheap method of obtaining rate constants for OH. reactions that compare well with those obtained by using pulse radiolysis.

Topics: Benzoates; Benzoic Acid; Chromatography, High Pressure Liquid; Deoxyribose; Edetic Acid; Ferrous Compounds; Formates; Free Radicals; Glucose; Hydroxylation; Mannitol; Spectrometry, Fluorescence; Thiourea

Topics: Formates; Thiourea