- Degradation of the Cellulosic Key Chromophore 5,8-Dihydroxy-[1,4]-naphthoquinone by Hydrogen Peroxide under Alkaline Conditions
-
5,8-Dihydroxy-[1,4]-naphthoquinone (DHNQ) is one of the key chromophores in cellulosic materials. Its almost ubiquitous presence in cellulosic materials makes it a target molecule of the pulp and paper industry's bleaching efforts. In the presented study, DHNQ was treated with hydrogen peroxide under alkaline conditions at pH 10, resembling the conditions of industrial hydrogen peroxide bleaching (P stage). The reaction mechanism, reaction intermediates, and final degradation products were analyzed by UV/vis, NMR, GC-MS, and EPR. The degradation reaction yielded C1-C4 carboxylic acids as the final products. Highly relevant for pulp bleaching are the findings on intermediates of the reaction, as two of them, 2,5-dihydroxy-[1,4]-benzoquinone (DHBQ) and 1,4,5,8-naphthalenetetrone, are potent chromophores themselves. While DHBQ is one of the three key cellulosic chromophores and its degradation by H2O2 is well-established, the second intermediate, 1,4,5,8-naphthalenetetrone, is reported for the first time in the context of cellulose discoloration.
- Zwirchmayr, Nele Sophie,Hosoya, Takashi,Henniges, Ute,Gille, Lars,Bacher, Markus,Furtmüller, Paul,Rosenau, Thomas
-
p. 11558 - 11565
(2017/11/10)
-
- 2, 3-Butanediamide Epoxide Compound and Preparation Method and Use Thereof
-
Provided are a compound of formula I which can be used as a drug against small RNA virus infections, and optical isomers, pharmaceutically acceptable salts, solvates or hydrates thereof. Also provided are the preparation method of the compound, the method for using the compound for treating bacterial infections and the use of the compound in the preparation of a drug for preventing and/or treating viral diseases caused by small RNA viruses.
- -
-
Paragraph 0159
(2016/05/19)
-
- Regioselective Cleavage of Electron-Rich Double Bonds in Dienes to Carbonyl Compounds with [Fe(OTf)2(mix-BPBP)] and a Combination of H2O2 and NaIO4
-
A method for the regioselective transformation of dienes to carbonyl compounds has been developed. Electron-rich olefins react selectively to yield valuable aldehydes and ketones. The method is based on the catalyst [Fe(OTf)2(mix-BPBP)] with an oxidant combination of H2O2 (1.0 equiv.) and NaIO4 (1.5 equiv.); it uses mild conditions and short reaction times, and it outperforms other olefin cleavage methodologies. The combination of an Fe-based catalyst, [Fe(OTf)2(mix-BPBP)], and the oxidants H2O2 and NaIO4 can discriminate between electronically different double bonds and oxidatively cleave the electron-rich bond in dienes to yield aldehydes and ketones in a regioselective manner. The reaction requires mild conditions (0-50 C) and short reaction times (70 min).
- Spannring, Peter,Yazerski, Vital A.,Chen, Jianming,Otte, Matthias,Weckhuysen, Bert M.,Bruijnincx, Pieter C. A.,Klein Gebbink, Robertus J. M.
-
p. 3462 - 3466
(2015/08/06)
-
- Design, synthesis, and screen of cathepsin K inhibitors
-
We synthesized a series of epoxysuccinic acid derivatives and evaluated their in vitro cathepsin K inhibitory activity The screening results show that the potency of compounds 9e, 9d, 9p, 9j and 9k (IC50 ≤ 0.005 μmol/L) were equal to or greater than that of the lead compound 9a. Less hydrophobic compounds showed weaker potency, which can be explained by the hydrophobic nature of the cathepsin K binding pockets.
- Yu, Ying-Ying,Sun, Wei,Dong, Lei,Liu, Hai-Dong,Jiang, Dan,Xiao, Jun-Hai,Yang, Xiao-Hong,Li, Song
-
p. 715 - 718
(2013/07/26)
-
- Oxidation of some unsaturated acids by tetrakis (pyridine) silver dichromate: A kinetic and mechanistic study
-
The oxidation of a few unsaturated acids viz. maleic, fumaric, crotonic and cinnamic acids by tetrakis (pyridine) silver dichromate (TPSD) in dimethylsulphoxide (DMSO) leads to the formation of corresponding epoxide. The reaction is of first order with respect to TPSD and the acid. The reaction is catalysed by hydrogen ions. The hydrogen-ion dependence has the form : k obs = a + b [H+]. The oxidation of these acids was studied in nineteen different organic solvents. The solvent effect was analyzed by Kamlet's and Swain's multiparametric equations. Solvent effect indicated the importance of the cation-solvating power of the solvent. A mechanism involving a three-centre transition state has been postulated.
- Choudhary,Yajurvedi,Kumbhani,Shastri,Sharma, Vinita
-
scheme or table
p. 832 - 836
(2010/06/12)
-
- Design, Synthesis, and Evaluation of Aza-Peptide Epoxides as Selective and Potent Inhibitors of Caspases-1, -3, -6, and -8
-
Aza-peptide epoxides, a novel class of irreversible protease inhibitors, are specific for the clan CD cysteine proteases. Aza-peptide epoxides with an aza-Asp residue at P1 are excellent irreversible inhibitors of caspases-1, -3, -6, and -8 with second-order inhibition rates up to 1 910 000 M-1 s-1. In general, the order of reactivity of aza-peptide epoxides is S,S > R,R > trans > cis. Interestingly, some of the R,R epoxides while being less potent are actually more selective than the S,S epoxides. Our aza-peptide epoxides designed for caspases are stable, potent, and specific inhibitors, as they show little to no inhibition of other proteases such as the aspartyl proteases porcine pepsin, human cathepsin D, plasmepsin 2 from P. falciparum, HIV-1 protease, and the secreted aspartic proteinase 2 (SAP-2) from Candida albicans; the serine proteases granzyme B and α-chymotrypsin; and the cysteine proteases cathepsin B and papain (clan CA), and legumain (clan CD).
- James, Karen Ellis,Asgian, Juliana L.,Li, Zhao Zhao,Ekici, ?zlem Do?an,Rubin, John R.,Mikolajczyk, Jowita,Salvesen, Guy S.,Powers, James C.
-
p. 1553 - 1574
(2007/10/03)
-
- Kinetics and mechanism of oxidation of some unsaturated organic substrates by quinolinium chlorochromate
-
The oxidation of unsaturated organic compounds, viz. crotyl alcohol, allyl alcohol, crotonaldehyde and maleic acid by quinolinium chlorochromate (QCC) in acetic acid-water medium (50% v/v) leads to the formation of corresponding epoxide. The reaction is of first order each in QCC and the reductant. The reaction is catalysed by hydrogen ions. The increase in dielectric constant of the medium decreases the rate, while variation in ionic strength has no perceptible change in rate. The reaction rates have been determined at different temperatures and the activation parameters have been evaluated. The mechanism consistent with the observed results has been discussed.
- Mishra, Kanchan,Singh, Jai Veer,Pandey, Archna
-
-
- Configuration and enantioselective synthesis of the fungal metabolite WF14861
-
A short enantioselective synthesis of the cathepsine inhibitor WF14861 (1) from the funghi Colletotrichum sp. as well as of its diasteroisomer 21 is presented. Comparison of the NMR data of the final products and, in particular, of the [α]D values of the intermediates allowed the confirmation of the formerly proposed structure 1. In addition, the so far unknown absolute configuration of all three stereogenic centres of WF14861 could be established by this synthesis.
- Detterbeck, Richard,Hesse, Manfred
-
p. 222 - 232
(2007/10/03)
-
- Kinetics and mechanism of the oxidation of some unsaturated acids by quinolinium bromochromate
-
The oxidation of maleic, fumaric, crotonic and cinnamic acids by quinolinium bromochromate (QBC) in dimethylsulphoxide (DMSO) leads to the formation of corresponding epoxide. The reaction is of first order with respect to QBC and the acid. The reaction is catalysed by hydrogen ions. The hydrogen-ion dependence has the form: kobs = a + b [H+]. The oxidation of these acids was studied in nineteen different organic solvents. The solvent effect was analyzed by Kamlet's and Swain's multiparametric equations. Solvent effect indicated the importance of the cation-solvating power of the solvent. A mechanism involving a three-centre transition state has been postulated.
- Vyas, Shweta,Sharma, Pradeep K.
-
p. 820 - 823
(2007/10/03)
-
- Plaster retarding composition
-
The present invention is related to a calcium tartrate plaster retarding composition, characterised in that it has a mean particle size lower than 30 μm,The present invention is also related to the plaster comprising said composition and to the preparation process of said composition.
- -
-
-
- Aza-peptide epoxides: A new class of inhibitors selective for clan CD cysteine proteases
-
Aza-peptide epoxides, a new class of irreversible protease inhibitors, are specific for the clan CD cysteine proteases. The inhibitors have second-order rate constants up to 105 M-1 s-1, with the most potent epoxides having the S,S stereochemistry. The aza-Asn derivatives are effective legumain inhibitors, while the aza-Asp epoxides were specific for caspases. The inhibitors have little or no inhibition with other proteases such as chymotrypsin, papain, or cathepsin B.
- Asgian, Juliana L.,James, Karen Ellis,Li, Zhao Zhao,Carter, Wendy,Barrett, Alan J.,Mikolajczyk, Jowita,Salvesen, Guy S.,Powers, James C.
-
p. 4958 - 4960
(2007/10/03)
-
- KINETICS AND MECHANISM OF THE VANADATE-CATALYSED OXIDATION OF MALEIC ACID BY HYDROGEN PEROXIDE
-
Kinetics of the oxidation of maleic acid with hydrogen peroxide has been studied in aqueous acidic medium in the presence of Na3VO4 acting as a catalyst, at 40 deg C.The rate of the reaction is first oredr with respect to and but independent of .The oxidation rate is pH dependent.Change in ionic strength of the medium shows no effect on the reaction rate.Various activation parameters have been computed and a probable reaction mechanism satisfying the various kinetic parameters have been proposed.
- Agrawal, G. L.,Shrivastava, Alka
-
p. 751 - 756
(2007/10/02)
-
- A stereocontrolled approach to electrophilic epoxides
-
Lithium t-butyl hydroperoxide (easily generated by addition of an alkyl-lithium to anhydrous t-butyl hydroperoxide in THF solution) is a powerful reagent for the epoxidation of electrophilic alkenes at -20 to 0 °C under full stereocontrol. Thus αβ-unsaturated esters, sulphones, sulphoximines, and amides are readily epoxidised with complete regio- and stereo-specificity and with considerable chiroselectivity (20-100%) when appropriate chiral auxiliaries such as menthyl, 8-phenylmenthyl, or a camphor-sulphonamide derivative are used. Asymmetric αβ-unsaturated sulphoximines undergo epoxidation with 100% diastereoselectivity. The only exceptions to stereocontrol noted are heavily substituted maleate esters such as di-t-butyl maleate. The αβ-epoxy amides are shown to be valuable sources of the corresponding epoxy ketones by treatment with an organolithium, allowing a stereo- and chemoselective entry in high yield to these useful intermediates.
- Meth-Cohn, Otto,Moore, Clive,Taljaard, Heinrich C.
-
p. 2663 - 2674
(2007/10/02)
-
- Method of producing tartaric acid
-
Tartaric acid is produced by epoxidizing acid calcium maleate with aqueous hydrogen peroxide in the presence of a tungstic acid-containing catalyst to produce sparingly soluble acid calcium cis-epoxysuccinic acid, which is suspended in a solvent medium comprising an organic solvent or a mixture of organic solvent and water and treated with sulphuric acid. Calcium sulphate is formed and separated and the liberated organic acids consisting essentially of epoxysuccinic acid are then hydrolyzed in an aqueous medium to form tartaric acid. The organic solvent may be one in which epoxysuccinic acid is soluble and may be immiscible or miscible with water. If the solvent is imiscible with water the epoxysuccinic acid may be transferred to the aqueous medium in which it is hydrolyzed by liquid-liquid extraction. The epoxysuccinic acid may be crystallized out of the solvent medium and thereafter dissolved in water for the hydrolysis, or, if the organic solvent is miscible with water and the solvent medium comprises water, the organic solvent may be distilled off to leave the epoxysuccinic acid in the aqueous medium in which hydrolysis can be effected. Various organic solvents are disclosed as suitable.
- -
-
-