- Kinetic and mechanistic study of glucose isomerization using homogeneous organic br?nsted base catalysts in water
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The isomerization of glucose to fructose represents a key intermediate step in the conversion of cellulosic biomass to fuels and renewable platform chemicals, namely, 5-hydroxymethyl furfural (HMF), 2,5-furandicarboxylic acid (FDCA), and levulinic acid (LA). Although both Lewis acids and Br?nsted bases catalyze this reaction, the base-catalyzed pathway received significantly less attention due to its lower selectivity to fructose and the poor yields achieved (1H NMR spectroscopy. Pathways leading to isomerization and degradation of the monosaccharides have been identified through careful experimentation and comparison with previously published data. Kinetic isotope effect experiments were carried out with labeled glucose to validate the rate-limiting step. The ex situ characterization of the reaction products was confirmed using in situ 1H NMR studies. It is shown that unimolecular (thermal) and bimolecular (alkaline) degradation of fructose can be minimized independently by carefully controlling the reaction conditions. Fructose was produced with 32% yield and 64% selectivity within 7 min.
- Carraher, Jack M.,Fleitman, Chelsea N.,Tessonnier, Jean-Philippe
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- The production, purification and characterisation of two novel α-D-mannosidases from Aspergillus phoenicis
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1,6-α-D-Mannosidase from Aspergillus phoenicis was purified by anion-exchange chromatography, chromatofocussing and size-exclusion chromatography. The apparent molecular weight was 74 kDa by SDS-PAGE and 81 kDa by native-PAGE. The isoelectric point was 4.6. 1,6-α-d-Mannosidase had a temperature optimum of 60°C, a pH optimum of 4.0-4.5, a Km of 14 mM with α-d-Manp-(1→6)-d-Manp as substrate. It was strongly inhibited by Mn2+ and did not need Ca2+ or any other metal cofactor of those tested. The enzyme cleaves specifically (1→6)-linked mannobiose and has no activity towards any other linkages, p-nitrophenyl-α-d- mannopyranoside or baker's yeast mannan. 1,3(1,6)-α-d-Mannosidase from A. phoenicis was purified by anion-exchange chromatography, chromatofocussing and size-exclusion chromatography. The apparent molecular weight was 97 kDa by SDS-PAGE and 110 kDa by native-PAGE. The 1,3(1,6)-α-d-mannosidase enzyme existed as two charge isomers or isoforms. The isoelectric points of these were 4.3 and 4.8 by isoelectric focussing. It cleaves α-d-Manp-(1→3)-d- Manp 10 times faster than α-d-Manp-(1→6)-d-Manp, has very low activity towards p-nitrophenyl-α-d-mannopyranoside and baker's yeast mannan, and no activity towards α-d-Manp-(1→2)-d-Manp. The activity towards (1→3)-linked mannobiose is strongly activated by 1 mM Ca 2+ and inhibited by 10 mM EDTA, while (1→6)-activity is unaffected, indicating that the two activities may be associated with different polypeptides. It is also possible that one polypeptide may have two active sites catalysing distinct activities.
- Athanasopoulos, Vasileios I.,Niranjan, Keshavan,Rastall, Robert A.
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- Epicoccamide, a novel secondary metabolite from a jellyfish-derived culture of Epicoccum purpurascens.
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From the inner tissue of the jellyfish Aurelia aurita a marine strain of the fungus Epicoccum purpurascens was obtained. After mass cultivation the fungus was investigated for its secondary metabolite content and found to contain the new, and most unusual tetramic acid derivative, epicoccamide (1). Epicoccamide is quite unusual since it is composed of three biosynthetically distinct subunits; glycosidic, fatty acid and tetramic acid (amino acid). The structure of the new compound was elucidated using spectroscopic methods, mainly 1D and 2D NMR, ESI-MS, and chemical degradations.
- Wright, Anthony D,Osterhage, Claudia,Koenig, Gabriele M
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- Purification and characterization of α-D-mannosidase from the seeds of Kaya, Torreya nucifera
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Alpha-D-mannosidase was purified from the extract of seeds of Kaya, Torreya nucifera. The purified enzyme had a molecular mass of ~ 3.6 × 105 daltons. This enzyme had an optimum pH at 4.5, and was stable at pH between 5.5 and 6.5. This enzyme appeared to be a metal enzyme containing Zn2-. The enzyme hydrolyzed p-nitrophenyl-α-D-mannoside, methyl-α-D-mannoside, α-1-→3-mannobiose, and α-1-→6-mannobiose, with Km of 0.785 mM, 0.236 M, 2.505 mM, and 0.268 mM, respectively. The hydrolysis of various α-linked mannobioses indicated that the enzyme hydrolyzes the α-mannobioses in the order of α-(1→2)> -(1→6)> -(1→3).
- Shikoo, Tomomi,Ohtani, Kimiko,Huchigami, Kyoko,Nakatani, Masato,Yuasa, Isao,Misaki, Akira
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- Epimerization of carbohydrates via stannylene acetals. A practical synthesis of D-Talose
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When treated with Bu2SnO in a suitable solvent, reducing sugars preferentially form 1,2-O-stannylene acetals and, on prolonged treatment with a slight excess of the reagent at reflux temperature, they undergo epimerization. This allows simple preparation of rare monosaccharides from readily available, unprotected starting materials. The process is equilibrium driven, and the equilibrium is shifted largely in favor of structures having an axial hydroxyl group at position 2.
- Hodosi, Gyoergy,Kovac, Pavol
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- C-2 Epimerization of Aldoses Promoted by Combination of Monoamines and Alkaline Earth or Rare Earth Metal Ions, Involving a Rearrangement of the Carbon Skeleton
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Aldoses are rapidly epimerized at C-2 by combination of alkaline earth or rare earth metal ions (Ca2+, Sr2+,Pr3+, or Ce3+)and monoamines (triethlamine etc.). (13)C NMR studies using -D-glucose of the Ca2+ system revealed that this reaction proceeds via the stereospecific rearrangement of carbon skeleton.
- Tanase, Tomoaki,Murata, Takashi,Yano, Shigenobu,Hidai, Masanobu,Yoshikawa, Sadao
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- The loop structure of Actinomycete glycoside hydrolase family 5 mannanases governs substrate recognition
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Endo-β-1,4-mannanases from Streptomyces thermolilacinus (StMan) and Thermobifida fusca (TfMan) demonstrated different substrate specificities. StMan hydrolyzed galactosylmannooligosaccharide (GGM5; 6III,6IV-α-d-galactosyl mannopentaose) to GGM3 and M2, whereas TfMan hydrolyzed GGM5 to GGM4 and M1. To determine the region involved in the substrate specificity, we constructed chimeric enzymes of StMan and TfMan and evaluated their substrate specificities. Moreover, the crystal structure of the catalytic domain of StMan (StMandC) and the complex structure of the inactive mutant StE273AdC with M6 were solved at resolutions of 1.60 and 1.50 ?, respectively. Structural comparisons of StMandC and the catalytic domain of TfMan lead to the identification of a subsite around -1 in StMandC that could accommodate a galactose branch. These findings demonstrate that the two loops (loop7 and loop8) are responsible for substrate recognition in GH5 actinomycete mannanases. In particular, Trp281 in loop7 of StMan, which is located in a narrow and deep cleft, plays an important role in its affinity toward linear substrates. Asp310 in loop8 of StMan specifically bound to the galactosyl unit in the -1 subsite.
- Kumagai, Yuya,Yamashita, Keitaro,Tagami, Takayoshi,Uraji, Misugi,Wan, Kun,Okuyama, Masayuki,Yao, Min,Kimura, Atsuo,Hatanaka, Tadashi
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- Chemical constituents and antioxidant, anti-inflammatory and anti-tumor activities of melilotus officinalis (linn.) pall
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Two new p-hydroxybenzoic acid glycosides, namely p-hydroxybenzoic acid-4-O-α-D-manopyranosyl-(1 → 3)-α-L-rhamnopyranoside (compound 1) and 4-O-α-L-rhamnopyran-osyl-(1 → 6)-α-D-manopyranosyl-(1 → 3)-α-L-rhamnopyranoside (compound 2), and seven known compounds, compound 3, 6, 7 (acid components), compound 8, 9 (flavonoids), compound 4 (a coumarin) and compound 5 (an alkaloid), were isolated from the 70% ethanol aqueous extract of the aerial parts of Melilotus officinalis (Linn.) Pall. The structures of all compounds were elucidated by use of extensive spectroscopic methods Infrared Spectroscopy (IR), High resolution electrospray ionization mass spectrometry (HR-ESI-MS), and1H and13C-NMR). Sugar residues obtained after acid hydrolysis were identified by high-performance liquid chromatography (HPLC). The antioxidant activity of all the compounds was evaluated by 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS+) and 1,1-diphenyl-2-picrylhydrazyl (DPPH). The anti-inflammatory effects of the compounds were also evaluated in lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages. All compounds were shown to inhibit LPS-induced nitric oxide (NO) and prostaglandin E 2 (PGE 2) production by suppressing the expression of inducible NO synthase (iNOS) and cyclooxygenase-2 (COX-2), respectively, in LPS-stimulated RAW 264.7 cells. The inhibitory effect of all the compounds on MCF-7 cells was determined by Cell Counting Kit-8 (CCK-8) method. The results showed that compounds 1, 2, 7, 8, 9 exhibited better antioxidant activity compared to the other compounds. compounds 1–9 had different inhibitory effects on the release of NO, TNF-α and IL-6 in LPS-stimulated RAW264.7 cells by LPS, of which compound 7 was the most effective against inflammatory factors. compounds 1 and 2 have better antitumor activity compared to other compounds. Further research to elucidate the chemical composition and pharmacological effects of Melilotus officinalis (Linn.) Pall is of major importance towards the development and foundation of clinical application of the species.
- Liu, Yu-Ting,Gong, Pei-Han,Xiao, Feng-Qin,Shao, Shuai,Zhao, Da-Qing,Yan, Ming-Ming,Yang, Xiu-Wei
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- Inhibitory effects of terpenoids from the fermented broth of the ascomycete stilbohypoxylon elaeicola YMJ173 on nitric oxide production in RAW264.7 macrophages
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A series of six isopimarane-type diterpene glycosides, along with an eremophilane-type sesquiterpene, i.e., elaeicolasides A-C (1-3, resp.), 16-(α-D-mannopyranosyloxy)isopimar-7-en-19-oic acid (4), hymatoxin K (5), hymatoxin L (6), and elaeicolalactone (7), were isolated from the AcOEt extract of the fermented broth of Stilbohypoxylon elaeicola YMJ173. Among these, 1-3 and 7 are new compounds based on their spectroscopic data and sugar composition analysis. The effects of 1-7 on the inhibition of nitric oxide (NO) production in lipopolysaccharide (LPS)-activated murine macrophage RAW264.7 cells were evaluated. All these compounds inhibited NO production, detected as nitrite in the culture medium, in activated macrophages without any cytotoxicity at a concentration of 100μM. Among these compounds, 2 showed a significant activity with the average maximum inhibition (Emax) and median inhibitory concentration (IC50) values of 93.3±0.5% and 79.3±0.4μM, respectively. Copyright
- Wang, Guei-Jane,Liang, Wen-Li,Ju, Yu-Ming,Yang, Wen-Bin,Chang, Ya-Wen,Lee, Tzong-Huei
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- Biochemical characterization of a recombinant acid phosphatase from Acinetobacter baumannii
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Genomic sequence analysis of Acinetobacter baumannii revealed the presence of a putative Acid Phosphatase (AcpA; EC 3.1.3.2). A plasmid construct was made, and recombinant protein (rAcpA) was expressed in E. coli. PAGE analysis (carried out under denaturing/ reducing conditions) of nickel-affinity purified protein revealed the presence of a nearhomogeneous band of approximately 37 kDa. The identity of the 37 kDa species was verified as rAcpA by proteomic analysis with a molecular mass of 34.6 kDa from the deduced sequence. The dependence of substrate hydrolysis on pH was broad with an optimum observed at 6.0. Kinetic analysis revealed relatively high affinity for PNPP (Km = 90 μM) with Vmax, kcat, and Kcat/Km values of 19.2 pmoles s-1, 4.80 s-1(calculated on the basis of 37 kDa), and 5.30 × 104 M-1s-1, respectively. Sensitivity to a variety of reagents, i.e., detergents, reducing, and chelating agents as well as classic acid phosphatase inhibitors was examined in addition to assessment of hydrolysis of a number of phosphorylated compounds. Removal of phosphate from different phosphorylated compounds is supportive of broad, i.e., 'nonspecific' substrate specificity; although, the enzyme appears to prefer phosphotyrosine and/or peptides containing phosphotyrosine in comparison to serine and threonine. Examination of the primary sequence indicated the absence of signature sequences characteristic of Type A, B, and C nonspecific bacterial acid phosphatases.
- Smiley-Moreno, Elizabeth,Smith, Douglas,Yu, Jieh-Juen,Cao, Phuong,Arulanandam, Bernard P.,Chambers, James P.
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- New phenolic glycosides from Anemone chinensis Bunge and their antioxidant activity
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ABATRACT: Nine compounds, five phenolic glycosides (1, 2, 4–6), three phenylpropanoids (7–9), and a furanone glycoside (3), were isolated from aqueous soluble extract of the dried roots of Anemone chinensis Bunge. The structures of new compounds (1–4) were elucidated by comprehensive spectroscopic data analysis as well as chemical evidence. Pulsatillanin A (1) demonstrated significant antioxidant effects through scavenging free radical in DPPH assay, and relieved the oxidative stress in LPS-induced RAW 264.7 cells by reducing ROS production, enhancing antioxidant enzyme SOD activity, replenishing depleted GSH in a dose-dependent manner. Western blot analysis revealed that 1 showed antioxidant activity via activating Nrf2 signaling pathway.
- Zhang, Zeng-Guang,Li, Yuan-Yuan,Lin, Bin,Guan, Pei-Pei,Mu, Yu,Qiao, Wen-Jun,Zhang, Jing-Sheng,Huang, Xue-Shi,Han, Li
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supporting information
(2021/05/10)
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- Tuning Ca-Al-based catalysts' composition to isomerize or epimerize glucose and other sugars
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One of the key reactions to achieve good productivity in the transformations of cellulose derived from biomass feedstocks is the isomerization of glucose to fructose, the latest being the platform molecule for obtaining other important derivatives. In this work, Ca-Al containing catalysts based on hydrotalcite-type derived materials were used to perform the selective isomerization of glucose to fructose, and the selective epimerization of glucose to mannose, using water as the solvent under mild reaction conditions. The catalysts showed high activity (conversion = 51-87%), and excellent selectivity (63-88%) towards fructose, compared with the current industrial process based on the glucose transformation via biocatalysis. It was also possible to modulate the selectivity towards fructose or mannose by tuning the amount of basic sites of the catalysts and their composition. The combination of basic and acid sites present in the Ca-Al-based catalysts plays a key role in the reaction, a fact that is discussed in the text together with other important operational parameters. The stability and recyclability of the catalysts were tested, detecting only a small activity loss after 5 consecutive runs. The synthesis of the catalysts and their characterization are also discussed since they are one of the few cases found in the literature of this kind of hydrotalcite-type material with such a high level of Ca incorporation. Some green metrics, such as E-factor, have been calculated to evaluate our system as an environmentally friendly process.
- Ventura, Maria,Cecilia, Juan A.,Rodríguez-Castellón, Enrique,Domine, Marcelo E.
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p. 1393 - 1405
(2020/03/11)
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- A synthesis method of D - mannose (by machine translation)
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The invention belongs to the technical field of medical synthesis, in particular to a brand-new D - mannose synthesis method, the present invention in order to D - mannitol as raw materials, through the end of the first TBDMSCl to two primary hydroxy protection, through the benzyl or acyl group to the remaining four hydroxyl protection, subsequently removing a primary hydroxy silicon ether protecting group, after after oxidation, removing all hydroxy protecting group, to finally obtain the D - mannose. The method mild reaction, synthetic high yield, the operation is simple, and is suitable for industrial large-scale production. (by machine translation)
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- The tertiary-butyl group: Selective protection of the anomeric centre and evaluation of its orthogonal cleavage
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The tertiary-butyl group has not been examined extensively as a protecting group. In this work, we describe the synthesis of tert-butyl glycosides via the Fischer glycosylation protocol. Furthermore, its utility as a temporary anomeric protecting group was evaluated. A range of differentially protected monosaccharides was used to investigate the stability of the tert-butyl group upon the introduction of other protecting groups; and compatibility of its cleavage in the presence of the latter.
- Subratti, Afraz,Jalsa, Nigel Kevin
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p. 2082 - 2085
(2018/05/04)
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- Regulating Cofactor Balance In Vivo with a Synthetic Flavin Analogue
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A novel strategy to regulate cofactor balance in vivo for whole-cell biotransformation using a synthetic flavin analogue is reported. High efficiency, easy operation, and good applicability were observed for this system. Confocal laser scanning microscopy was employed to verify that the synthetic flavin analogue can directly permeate into Escherichia coli cells without modifying the cell membrane. This work provides a promising intracellular redox regulatory approach to construct more efficient cell factories.
- Tan, Zhuotao,Zhu, Chenjie,Fu, Jingwen,Zhang, Xiaowang,Li, Ming,Zhuang, Wei,Ying, Hanjie
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supporting information
p. 16464 - 16468
(2018/11/23)
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- Porous Tin-Organic Frameworks as Selective Epimerization Catalysts in Aqueous Solutions
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Epimerization of sugars is a carbon-efficient route not only to produce rare carbohydrates but also to extend the product scope for chemical production in future biorefineries. Industrially available catalysts for epimerization are limited mainly to soluble Mo(VI) species as well as substrate-specific epimerases. Here we report highly active and selective tin-organic frameworks (Sn-OF) as solid catalysts for the epimerization of aldoses at the C-2 position, such as the conversion of glucose to mannose. The reaction proceeds via a carbon skeleton rearrangement, that is, through breaking of a C-2/C-3 carbon bond and formation of a C-1/C-3 bond. Partially hydrolyzed Ph3Sn-OH sites were found to be the catalytically active centers. Our results suggest that the high catalytic activity of Sn-OFs for the epimerization is determined by (1) Lewis acidity of tin; (2) free Sn-OH groups; and (3) the high hydrophobicity of organic linkers applied in the aqueous solutions.
- Delidovich, Irina,Hoffmann, Andreas,Willms, Andrea,Rose, Marcus
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p. 3792 - 3798
(2017/06/19)
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- NOVEL METHODS OF ISOMERIZING CARBOHYDRATES
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The invention provides a method of isomerizing a sugar into fructose using a calcium salt and an organic base. In certain embodiments, the sugar is glucose and/or mannose.
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Paragraph 0064; 0065; 0066; 0067; 0069; 0070; 0072-0079
(2017/07/31)
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- PROCESS FOR THE CONVERSION OF SUGARS TO LACTIC ACID AND 2-HYDROXY-3-BUTENOIC ACID OR ESTERS THEREOF COMPRISING A METALLO-SILICATE MATERIAL AND A METAL ION
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The present invention regards metallo-silicate materials comprising a metal ion selected from one or more of the group consisting of potassium ions, sodium ions, lithium ions, rubidium ions and caesium ions. The materials are useful preparing lactic acid and 2-hydroxy-3-butenoic acid or esters thereof from a sugar.
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Paragraph 0054; 0055; 0056; 0057; 0058
(2017/03/21)
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- Characterization and antitumor activities of a water-soluble polysaccharide from Ampelopsis megalophylla
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Abstract A water-soluble polysaccharide named as AMP was isolated and purified from the leaves of Ampelopsis megalophylla by DEAE-52 Cellulose and Sephadex G-100 column chromatography. AMP had an average molecular weight of about 8.4 × 104 Da and was composed of galactose (Gal), mannose (Man), glucose (Glc), arabinose (Ara), and rhamnose (Rha) in a molar ratio of 2.7:1.6:1.1:0.6:0.3. After 10 days of AMP (50, 100, and 200 mg/kg) treatment once daily in tumor-bearing mice, AMP oral administration could inhibit the growth of transplantable Sarcoma 180 (S180) tumor in mice and increase the spleen index and body weight. Furthermore, AMP also promote splenocytes' proliferation induced by concanavalin A (ConA) and lipopolysaccharide (LPS), strengthen peritoneal macrophages to devour neutral red and increase the production of interleukin-2 (IL-2), tumor necrosis factor-alpha (TNF-α), and interferon-gamma (IFN-γ) in serum. These results suggest that AMP had clear antitumor activity, which might be related to its regulation of immune function in mice.
- Xie, Xianfei,Wang, Jianwu,Zhang, Hanping
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- Zemplén transesterification: A name reaction that has misled us for 90 years
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We demonstrated that using NaOH and NaOMe in methanol for deacylation are identical, indicating that the Zemplén condition has been misleading us for almost 90 years. The traditional base-catalyzed mechanism cannot be used to explain our results. We propose that H-bond complexes play key roles in the base-catalyzed process, explaining why deacylation in methanol can be catalyzed by hydroxide.
- Ren, Bo,Wang, Meiyan,Liu, Jingyao,Ge, Jiantao,Zhang, Xiaoling,Dong, Hai
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supporting information
p. 1390 - 1394
(2015/03/18)
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- Glucose dehydration to 5-hydroxymethylfurfural by a combination of a basic zirconosilicate and a solid acid
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A recently reported layered zirconosilicate Na2ZrSi4O11 displays good activity in the isomerization of glucose to fructose in water at mild conditions. Part of the activity derives from the homogeneous base-catalyzed reaction due to exchange of the sodium ions of the layered zirconosilicate in water. Following ion-exchange, the isomerization is mainly catalyzed by the basic sites of the re-used heterogeneous zirconosilicate catalyst. Combined with the solid acid Amberlyst-15, 5-hydroxymethylfurfural (5-HMF) can be produced from glucose in a one-pot reaction. In a THF/H2O mixture solvent system, 5-HMF was obtained with 45 % selectivity at 87 % glucose conversion at a temperature of 180 °C in 1.5 h. Graphical Abstract: [Figure not available: see fulltext.]
- Yue, Chaochao,Rigutto, Marcello S.,Hensen, Emiel J. M.
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p. 2121 - 2128
(2015/02/19)
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- Catalytic activity and stability of hydrophobic Mg-Al hydrotalcites in the continuous aqueous-phase isomerization of glucose into fructose
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The aqueous-phase isomerization of glucose into fructose, catalyzed by Mg-Al hydrotalcites, has been investigated under batch and continuous conditions. A commercial hydrotalcite with a hydrophobic surface modification and two hydrophilic hydrotalcites in carbonate form, or with OH- anions in the interlayer space, served as catalysts. With the hydrophobic hydrotalcite a lower conversion but superior selectivity to fructose could be demonstrated, reaching above 92% selectivity at 30% conversion. The observed by-products confirm retroaldolization of glucose and fructose as the main side reactions causing catalyst deactivation via adsorption. Additionally, acidic degradation products such as lactic acid cause neutralization of the hydrotalcites facilitating leaching of the Mg2+ ions. Fructose contributes a greater extent to by-product formation. Applying continuous operation conditions, fructose is removed from the reaction mixture. Therefore, by-product formation is notably suppressed and catalyst stability increases. During 70 to 100 h time-on-stream a slow deactivation of the hydrophobic hydrotalcite occurs. Regeneration can be achieved via calcination and treatment in an aqueous sodium n-dodecyl sulfate solution to introduce dodecyl sulfate anions to the interlayer space of the hydrotalcite, restoring the hydrophobic material properties.
- Delidovich,Palkovits
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p. 4322 - 4329
(2015/01/09)
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- Comparison of cellobiose and glucose transformation to ethylene glycol
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Cellobiose was used as a model feedstock to probe the reaction pathways of cellulose to ethylene glycol (EG). Its reactivity was compared with that of glucose using a catalyst composed of H2WO4 and Ru/C. EG can be produced by both the direct retro-aldol condensation of cellobiose and the retro-aldol condensation of glucose derived from cellobiose hydrolysis. The direct retro-aldol condensation of cellobiose further promoted the hydrolysis of cellobiose. Cellobiose has a lower reactivity for retro-aldol condensation than glucose, which decreased the formation rate of glycolaldehyde and made it more matched with the subsequent hydrogenation rate, thus leading to increased yield of EG from cellobiose.
- Zhang, Junying,Yang, Xiaofeng,Hou, Baolin,Wang, Aiqin,Li, Zhenlei,Wang, Hua,Zhang, Tao
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p. 1811 - 1817
(2015/09/28)
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- Comparative analysis of glycoside hydrolases activities from phylogenetically diverse marine bacteria of the genus Arenibacter
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A total of 16 marine strains belonging to the genus Arenibacter, recovered from diverse microbial communities associated with various marine habitats and collected from different locations, were evaluated in degradation of natural polysaccharides and chromogenic glycosides. Most strains were affiliated with five recognized species, and some presented three new species within the genus Arenibacter. No strains contained enzymes depolymerizing polysaccharides, but synthesized a wide spectrum of glycosidases. Highly active β-N- acetylglucosaminidases and α-N-acetylgalactosaminidases were the main glycosidases for all Arenibacter. The genes, encoding two new members of glycoside hydrolyses (GH) families, 20 and 109, were isolated and characterized from the genomes of Arenibacter latericius. Molecular genetic analysis using glycosidase-specific primers shows the absence of GH27 and GH36 genes. A sequence comparison with functionally-characterized GH20 and GH109 enzymes shows that both sequences are closest to the enzymes of chitinolytic bacteria Vibrio furnissii and Cellulomonas fimi of marine and terrestrial origin, as well as human pathogen Elisabethkingia meningoseptica and simbionts Akkermansia muciniphila, gut and non-gut Bacteroides, respectively. These results revealed that the genus Arenibacter is a highly taxonomic diverse group of microorganisms, which can participate in degradation of natural polymers in marine environments depending on their niche and habitat adaptations. They are new prospective candidates for biotechnological applications due to their production of unique glycosidases.
- Bakunina, Irina,Nedashkovskaya, Olga,Balabanova, Larissa,Zvyagintseva, Tatyana,Rasskasov, Valery,Mikhailov, Valery
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p. 1977 - 1998
(2013/07/26)
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- Structural characterization of the core oligosaccharide isolated from the lipopolysaccharide of the psychrophilic bacterium Colwellia psychrerythraea strain 34H
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Cold-adapted bacteria are microorganisms that thrive at very low temperatures in permanently cold environments (0-10 °C). Their ability to survive under these harsh conditions is the result of molecular evolution and adaptations, which include the structural modification of the phospholipid membrane. To give insight into the role of the membrane in the mechanisms of adaptation to low temperature, the characterization of other cell-wall components is necessary. Among these components, the lipopolysaccharides are complex amphiphilic macromolecules embedded in the outer leaflet of the external membrane, of which they are the major constituents. The cold-adapted Colwellia psychrerythraea 34H bacterium, living in deep sea and Arctic and Antarctic sea ice, was cultivated at 4 °C. The lipooligosaccharide (LOS) was isolated and analysed by means of chemical analysis. Then it was degraded either by mild hydrazinolysis (O-deacylation) or hot KOH (4 M; N-deacylation). Both products were investigated in detail by 1H and 13C NMR spectroscopy and by ESI FT-ICR mass spectrometry. The oligosaccharide portion consists of a unique and very short species with the following general structure: α-L-Col-(1→2)-α-D-GalA-(1→2)-α-D-Man-[3-P-D-Gro] -(1→5)-α-D-Kdo-4-P-Lipid-A. The structural characterization of the lipooligosaccharide from the steno-psychrophilic bacterium Colwellia psychrerythraea strain 34H has been achieved by means of chemical analysis, mass spectrometry, and NMR spectroscopy experiments. The data revealed a very short, negatively charged, and unique oligosaccharide, lacking heptose residues. Copyright
- Carillo, Sara,Pieretti, Giuseppina,Lindner, Buko,Parrilli, Ermenegilda,Filomena, Sannino,Tutino, Maria Luisa,Lanzetta, Rosa,Parrilli, Michelangelo,Corsaro, Maria Michela
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p. 3771 - 3779
(2013/07/26)
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- Regenerative labeling of saccharides
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A simple method for regenerative labeling of saccharides is devised by using (naphth-2-ylmethoxy)amine or N-methyl-(naphth-2-ylmethoxy)amine. The naphthyl group is optically responsive to facilitate the separation of labeled saccharides, which are subsequently reverted to the parental saccharides by one-pot hydrogenolysis-hydrolysis using co-catalysts Pd(OH)2 and HCl under an atmosphere of H2. The mechanistic study indicates that the naphthylmethyl group plays an essential role in the initial hydrogenolysis, followed by in situ hydrolysis, to regenerate the saccharides.
- Wen, Hao-Yu,Hsu, Peng-Hao,Chen, Guei-San,Fang, Jim-Min
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p. 9530 - 9533
(2013/07/27)
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- Oxidation of mannosyl oligosaccharides by hydroxyl radicals as assessed by electrospray mass spectrometry
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The hydroxyl radicals are widely implicated in oxidation of carbohydrates during biological and industrial processes being responsible for their structural modifications and causing functional damage. The identification of intermediate oxidation products is hampered by a lack of reliable sensible methods for their detection. In this study, the oxidation of two models of galactomannans (Man3 and GalMan2) has been studied in reaction with hydroxyl radical generated by Fenton reaction. The oxidation patterns were assessed using preparative ligand-exchange/size-exclusion chromatography (LEX/SEC) coupled with tandem electrospray mass spectrometry (ESI-MS/MS). This allowed the identification of derived oligosaccharides (OS) containing hexuronic, hexonic, pentonic and erythronic acid residues and neutral OS bearing hydroperoxy, hydrated carbonyl moieties and residues from pyranosyl ring cleavage. The depolymerization products have been also detected upon oxidation of oligomers. This study allowed developing a simple, effective 'fingerprinting' protocol for detecting the damage done to mannans by oxidative radicals.
- Tudella, Joana,Nunes, Fernando M.,Paradela, Rosa,Evtuguin, Dmitry V.,Domingues, Pedro,Amado, Francisco,Coimbra, Manuel A.,Barros, Ana I.R.N.A.,Domingues, M. Rosario M.
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scheme or table
p. 2603 - 2611
(2011/12/04)
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- Synthesis of some trifluoromethylated cyclodextrin derivatives and analysis of their properties as artificial glycosidases and oxidases
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Cyclodextrin derivatives containing trifluoromethyl groups at C6 of the A and D rings were synthesized for the purpose of creating artificial enzymes. The compounds were synthesized by perbenzylation of β-cyclodextrin followed by selective A,D-debenzylation according to Sinay. Subsequent oxidation to dialdehyde with Dess-Martin periodinane followed by addition of CF3 by using Arduengo carbene and TMSCF3 led to the C6- bistrifluoromethylated alcohols. These were either deprotected by hydrogenolysis or subjected to another round of oxidation to provide the corresponding ketones that were deprotected. The trifluoromethylated alcohols were found to be weak artificial enzymes catalysing hydrolysis of nitrophenyl glycosides at neutral pH with a kcat/kuncat of up to 56. It is proposed that this catalysis is analogues to the catalysis performed by related cyanohydrins. The trifluoro ketones were likewise weak articial enzymes catalysing oxidation of amines to nitro derivatives or alcohols to ketones with a kcat/k uncat of up to 133. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.
- Bjerre, Jeannette,Fenger, Thomas Hauch,Marinescu, Lavinia G.,Bols, Mikael
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p. 704 - 710
(2007/10/03)
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- Separation method
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The invention relates to a process of recovering galactose from a solution derived from plant-based biomass. In the process of the invention, the starting solution is subjected to one or more chromatographic fractionation steps, which may carried out with a strongly basic anion exchange resin and optionally with a strongly acid cation exchange resin, in any desired sequence, followed by recovering at least one fraction enriched in galactose. The galactose fraction thus obtained is further purified by crystallization to obtain crystalline galactose. The invention also relates to non-animal derived crystalline D-galactose.
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Page/Page column 7-8
(2008/06/13)
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- Remarkable supramolecular catalysis of glycoside hydrolysis by a cyclodextrin cyanohydrin
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(6AR,6DR)-6A,6D-di-C-cyano-β-cyclodextrin (3) was synthesized and shown to catalyze hydrolysis of nitrophenyl glycosides with the reaction following Michaelis-Menten kinetics. At pH 7.4 and 25 °C, hydrolysis of 4-nitrophenyl-β-glucopyranoside (2) was catalyzed with KM = 15 mM, kcat = 8.2 × 10-6 s-1, and kcat/kuncat = 1217. Catalysis was observed with concentration of 3 as low as 10 μM. Hydrolysis of the corresponding α-glucoside, α-galactoside, α-mannoside, and 2-nitrophenyl-β-galactoside was also catalyzed by 3, with kcat/kuncat ranging from 283 to 2147. A series of analogues of 3 was prepared and investigated for catalysis of the hydrolysis of 2: (6AR,6DR)-6A,6D-di-C-propyl-β-cyclodextrin (9) was not catalytic, while 6A,6D-di-C-cyano-6A,6D-dideoxy-β-cyclodextrin (12) had a low catalytic activity (kcat/kuncat = 4). A kcatkuncat = 48 was found for 6A,6D-dialdehydo-β-cyclodextrin dihydrate (11). It was proposed that 3 acts by general acid catalysis on the bound substrate. Copyright
- Ortega-Caballero, Fernando,Rousseau, Cyril,Christensen, Brian,Petersen, Torben Ellebaek,Bols, Mikael
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p. 3238 - 3239
(2007/10/03)
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- Four orders of magnitude rate increase in artificial enzyme-catalyzed aryl glycoside hydrolysis
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(6A6DR)-6A,6D-Di-C-cyano- β-cyclodextrin (1) and 6A,6D-di-C-cyano-α- cyclodextrin (2) were synthesized and shown to catalyze hydrolysis of aryl glycosides into glucose and phenol with a reaction following Michaelis-Menten kinetics. At pH 8.0 and 59 °C hydrolysis of 4-nitrophenyl α-glucopyranoside was catalyzed by 1 with KM = 10.5 ± 1.5 mM, kcat = 1.42(±0.09) × 10-4 s -1 and kcatk/uncat = 7922, Catalysis was observed with a concentration of 1 as low as 10 μM. Hydrolysis of the other aryl glycosides containing stereochemical variation in the sugar-moiety and 4-nitro-, 2-nitro-, 2-aldehydo-, and 2,4-dinitro- were also catalyzed by 1 and 2 with kcat/kuncat ranging from 4 to 7100. Hydrolysis of a phenyl β-D-glucoside or the thioglycoside tolylthio β-D-glucoside was also catalyzed. From a series of prepared analogues of 1 it was found that the catalysis was associated with the hydroxyl groups α to the nitril groups. The monocyanohydrin 6-C-cyano-β-cyclodextrin (3) was also found to catalyze the hydrolysis of 4-nitrophenyl β-glucopyranoside with k Cat/kuncat = 1356. It was proposed that the cyclodextrin cyanohydrins 1-3 catalyze the hydrolysis by general acid catalysis on the bound substrate.
- Ortega-Caballero, Fernando,Bjerre, Jeannette,Laustsen, Line Skall,Bols, Mikael
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p. 7217 - 7226
(2007/10/03)
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- Studies on kinetics and mechanism of iridium(III) catalysed cerium(IV) oxidation of D-mannitol and D-glucose in aqueous acid media
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The kinetics and mechanism of Ce(IV) oxidation of D-mannitol and D-glucose in aqueous H2SO4 media in the presence and absence of Ir(III) have been studied and compared under the conditions. [S]T?[Ce(IV)]T?[Ir]T, where [S]T gives the total substrate (D-mannitol or D-glucose) concentration and [Ir]T denotes the total concentration of Ir(III) catalyst added. Ir(III) has been found to catalyse the title reactions very efficiently even at trace concentration (ca. 10-6 to 10-7 mol dm-3). Under the kinetic conditions, both the uncatalysed and catalysed reactions take place simultaneously. The overall process shows a first order dependence on [Ce(IV)] and [S]T. The catalytic path is first order in [Ir]T suggested to involve the Ir(III)/Ir(IV) catalytic cycle. The process is acid catalysed and inhibited by [HSO4]. From the HSO4 dependence, both Ce(SO4)2+ and Ce(SO4)2 have been found kinetically active in D-mannitol oxidation while in D-glucose oxidation Ce(SO4)2 is the main kinetically active species under comparable conditions. The different kinetic parameters for both the Ir(III) catalysed and uncatalysed paths have been estimated.
- Roy, Aparna,Das, Asim K.
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p. 2468 - 2474
(2007/10/03)
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- Degradation of the Amadori compound N-(1-deoxy-d-fructos-1-yl)glycine in aqueous model systems
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The fate of the Amadori compound N-(1-deoxy-D-fructos-1-yl)glycine (DFG) was studied in aqueous model systems as a function of time and pH. The samples were reacted at 90 °C for up to 7 h while maintaining the pH constant at 5, 6, 7, or 8. Special attenti
- Davidek, Tomas,Clety, Nathalie,Aubin, Sandra,Blank, Imre
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p. 5472 - 5479
(2007/10/03)
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- New diterpene glycosides of the fungus Acremonium striatisporum isolated from a Sea Cucumber
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Three new diterpene glycosides, virescenosides O (1), P (2), and Q (3), have been isolated from a marine strain of Acremonium striatisporum KMM 4401 associated with the holothurian Eupentactafraudatrix. Their structures were determined on the basis of HRMALDIMS and NMR data as β-D-altropyranosido-19-isopimara-8(14),15-diene-7α,3β-diol (1), β-D-altropyranosido-19-7-oxoisopimara-8(9),15-diene-3β-ol (2), and β-D-mannopyranosido-19-isopimara-7,15-diene-3β-ol (3). The cytotoxic activity of the virescenosides was examined.
- Afiyatullov, Shamil Sh.,Kalinovsky, Anatoly I.,Kuznetsova, Tatyana A.,Isakov, Vladimir V.,Pivkin, Mikhail V.,Dmitrenok, Pavel S.,Elyakov, George B.
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p. 641 - 644
(2007/10/03)
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- Partial purification and characterization of a soybean β-glucosidase with high specific activity towards isoflavone conjugates
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A β-glucosidase with high specific activity towards isoflavone conjugates was purified from soybean [Glycine max] roots by high salt extraction from a low speed centrifugal pellet and subsequent anion and cation exchange chromatography. Purification required stabilization throughout fractionation in 10% glycerol. The enzyme is most likely a dimer (approximate Mr 165 kDa) with potential subunits of Mr 80 and/or 75 kDa. The pH and temperature optima are pH 6 and 30 °C, respectively. The enzyme was highly heat-stable. Of the various potential effectors examined, silver and mercury ions were the most inhibitory. The IC50 of silver ions was increased from 140 μM to 14 mM in the presence of 250 μM β-mercaptoethanol. Glucono-δ-lactone was not strongly inhibitory (IC50 24 mM). The activity was highly active against isoflavone conjugates, with a specificity constant 160-1000 fold higher for isoflavone conjugates over the generic chromogenic substrate, p-nitrophenyl β-glucoside. The enzyme was inactive against the flavonol glycosides tested. The partially purified enzyme had similar Km and kcat towards 7-O-glucosyl- and 7-O-glucosyl-6″-malonyl-isoflavones, suggesting that it may be able to cleave the esterified glucosyl conjugate. We hypothesize that the enzyme is involved in the release of daidzein and genistein, both of which play central roles in soybean defense.
- Hsieh, Ming-Ching,Graham, Terrence L
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p. 995 - 1005
(2007/10/03)
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- Substrate-dependent chemoselective aldose-aldose and aldose-ketose isomerizations of carbohydrates promoted by a combination of calcium ion and monoamines
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Epimerization of aldoses at C-2 has been extensively investigated by using various metal ions in conjunction with diamines, monoamines, and aminoalcohols. Aldoses are epimerized at C-2 by a combination of alkaline-earth or rare-earth metal ions (Ca2+, Sr2+, Pr3+, or Ce3+) and such monoamines as triethylamine. In particular, the Ca2+ -triethylamine system proved effective in promoting aldose-ketose isomerization as well as C-2 epimerization of aldoses. 13C NMR studies using D-(1-13C)glucose and D-(1-13C)galactose with the CaCl2 system in CD3OD revealed that the C-2 epimerization proceeds via stereospecific rearrangement of the carbon skeleton, or 1,2-carbon shift, and ketose formation proceeds partially through an intramolecular hydrogen migration or 1,2-hydride shift and, in part, via an enediol intermediate. These simultaneous aldose-aldose and aldose-ketose isomerizations showed interesting substrate-dependent chemoselectivity. Whereas the mannose-type aldoses having 2,3-erythro configuration (D-mannose, D-lyxose, and D-ribose) showed considerable resistance to both the C-2 epimerization and the aldose-ketose isomerization, the glucose-type sugars having 2,3-threo and 3,4-threo configurations, D-glucose and D-xylose, are mainly epimerized at C-2 and those having the 2,3-threo and 3,4-erythro configurations, D-galactose and D-arabinose, were mostly isomerized into 2-ketoses. These features are of potential interest in relevance to biomimic sugar transformations by metal ions.
- Tanase, Tomoaki,Takei, Tomoyuki,Hidai, Masanobu,Yano, Shigenobu
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p. 303 - 312
(2007/10/03)
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- Synthesis of glycosylamines: Identification and quantification of side products
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The synthesis of some glycosylamines (1-amino-1-deoxy-D-glucose, 1-amino-1-deoxy- D-galactose and 1-amino-1-deoxylactose) was carried out by treatment of the corresponding reducing sugars with ammonium hydrogencarbonate in concentrated ammonia. The reaction mixture was first analyzed by capillary electrophoresis with indirect absorbance detection and high performance anion-exchange chromatography with pulsed amperometric detection. Beside glycosylcarbamate, a known reaction by-product, fructose and lactulose were detected during the synthesis of 1-amino-1-deoxyglucose and 1-amino-1-deoxylactose, respectively. Quantification of glycosylamines was carried out by micellar electrokinetic chromatography with UV detection of their 9-fluorenylmethyloxycarbonyl (Fmoc) derivatives; lactulosylamine was thus detected in the synthesis mixture of 1-amino-1-deoxylactose. The Fmoc-glycosylamines were easily purified from the other components of the crude synthesis mixtures.
- Campa, Cristiana,Donati, Ivan,Vetere, Amedeo,Gamini, Amelia,Paoletti, Sergio
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p. 263 - 273
(2007/10/03)
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- Kinetics and mechanism of the reduction of chromium(VI) and chromium(V) by D-glucitol and D-mannitol
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The oxidation of D-glucitol and D-mannitol by CrVI yields the aldonic acid (and/or the aldonolactone) and CrIII as final products when an excess of alditol over CrVI is used. The redox reaction occurs through a CrVI → CrV → CrIII path, the CrVI → CrV reduction being the slow redox step. The complete rate laws for the redox reactions are expressed by: a) - d[CrVI]/dt = {kM2H [H-]2 +kMH [H+]}[mannitol][CrVI], where kM2H = (6.7 ± 0.3) · 10-2 M-3 S-1 and kMH = (9±2) · 10-3 M-2 S-1: b) - d [CrVI] /dt = {kG2H[H+]2 + kGH [H+]}[GLUCITOL][CrVI]. where kG2H = (8.5 ± 0.2) · 10-2 M-3 S-1 and kGH = (1.8 ± 0.1) · 10-2 M-2S-1 at 330. The slow redox steps are preceded by the formation of a CrVI oxy ester with λMAX 371 nm. at pH 4.5. In acid medium, intermediate CrV reacts with the substrate faster than CrVI does. The EPR spectra show that five- and six-coordinate oxo-CrV intermediates are formed, with the alditol or the aldonic acid acting as bidentate ligands. Pentacoordinate oxo-CrV species are present at any [H+], whereas hexacoordinate ones are observed only at pH V species are not observed, CrV complexes are stable enough to remain in solution for several days to months.
- Roldan, Viviana P.,Daier, Veronica A.,Goodman, Bernard,Santoro, Mabel I.,Gonzalez, Juan Carlos,Calisto, Nancy,Signorella, Sandra R.,Sala, Luis F.
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p. 3211 - 3228
(2007/10/03)
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- Stereoselective hydrolysis of p-nitrophenyl glycoside by boronic acid
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The alkaline hydrolysis of p-nitrophenyl α-D-glucoside, α-D-galactoside, and β-D-mannoside was selectively accelerated by addition of methyl boronic acid, as compared to that of the corresponding β-D-glucoside, α-D-galactoside, and α-D-mannoside. In the c
- Ohe, Takeru,Kida, Toshiyuki,Zhang, Wanbin,Nakatsuji, Yohji,Ikeda, Isao
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p. 1077 - 1078
(2007/10/03)
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- Rare keto-aldoses from enzymatic oxidation: Substrates and oxidation products of pyranose 2-oxidase
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Pyranose oxidases are known to oxidise D-glucose, D-xylose and L- sorbose to keto-aldoses, biochemically interesting compounds that may also be used for synthetic purposes in a variety of reactions. In this study pyranose oxidase from the basidiomycete Peniophora gigantea was investigated, and it was found that this enzyme is able to oxidise a broad variety of substrates very effectively. In analogy to its natural mode of action, most substrates are oxidised regioselectively in position 2. Certain compounds, however, are converted into 3-keto derivatives, and the enzyme even exhibits transfer potential, that is, disscharides are formed from β-glycosides of higher alcohols. Substrates that may be oxidised at C-2 in yields between 40-98% are D-allose, D-galactose, 6-deoxy-D-glucose, D-gentiobiose, α-D-glucopyranosyl fluoride and the very interesting 3-deoxy-D-glucose. 1,5-Anhydro-D-glucitol (1-deoxy-D-glucose) is very effectively oxidised in position 2 in 98% yield and additionally gives a product of dioxidation at C-2 and C-3 upon prolonged reaction time Selective oxidation at C-3 was found for 2-deoxy-D-glucose in very good yields and for methyl β-D-gluco- and methyl β-galactopyranoside in lower yields. All oxidation products were unequivocally characterised by NMR spectroscopy and/or chemical derivatisation. In addition, the kinetic data of the enzymatic reactions were determined for all substrates. On the basis of these data and the structural characteristics of the substrates, a model for the minimal structural requirements of the enzyme-substrate interaction is suggested. The enzyme presumably uses two different binding modes for the regioselective C-2 and the C-3 oxidations, which are described.
- Freimund, Stefan,Huwig, Alexander,Giffhorn, Friedrich,Koepper, Sabine
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p. 2442 - 2455
(2007/10/03)
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- Sequential removal of monosaccharides from the reducing end of oligosaccharides. I. A reaction between hydrazine and sugars having a glycosidic substituent on a carbon atom adjacent to the carbonyl group
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Hydrazine reacts smoothly with sugars having a glycosidic substituent when the glycosyl moiety is located on a carbon atom adjacent to an aldehyde or keto group, resulting in cleavage of the glycosidic linkage. In excess hydrazine, the released glycoside forms a hydrazone from which the reducing sugar may be recovered in high yields.
- Bendiak,Salyan,Pantoja
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p. 685 - 688
(2007/10/02)
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- C-2 Epimerization of Aldoses by Calcium Ion in Basic Solutions. A Simple System to Transform D-Glucose and D-Xylose into D-Mannose and D-Lyxose
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Aldoses were epimerized at C-2 by Ca2+ in aqueous or alcoholic basic solutions through a stereospecific rearrangement of the carbon skeletons of the aldose.The skeletal rearrangement was confirmed by 13C NMR analysis of the reaction products.The reaction of - and -D-glucose afforded - and -D-mannose, respectively, as major products.The effects of metal ions, bases, and solvents were examined, and it was found that a high concentration of Ca2+ and a base (>pH 12.3) were especially effective for the present rearrangement.Separation of the reaction products was also effected by using Ca2+ cation-exchange chromatography.Thus, under the optimized conditions, D-mannose and D-lyxose, which are rare in nature and expensive, were easily obtained in high isolated yields from D-glucose and D-xylose, respectively.
- Yanagihara, Ryoji,Soeda, Kaori,Shiina, Sumito,Osanai, Shuichi,Yoshikawa, Sadao
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p. 2268 - 2272
(2007/10/02)
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- Epimerization of Aldoses Catalysed by Self-organized Metallomicelles in an Aqueous Solution
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Nickel(II) complexes coordinated with long chain N-alkylated ethylenediamine ligands were synthesized.It was found that the complexes possessed a marked C-2 epimerization activity for aldoses in aqueous media.In contrast, a short chain diamine nickel(II) complex had little activity.The agreement between the formation of micelles and the enhancement of epimerization was clearly recognized.Amphiphilic complexes formed "metallomicelles" which coordinated the aldoses and produced a new ternary complex composed of nickel, diamine and sugar.The stereospecific epimerization occurred in this aggregate accompanied by carbon skeleton rearrangement.One explanation for the high epimerizing ability of the amphiphilic nickel complex is the accumulation effect of nickel ion and ethylenediamine at the micelle surface.
- Osanai, Shuichi,Yanagihara, Ryoji,Uematsu, Kimitake,Okumura, Atsuo,Yoshikawa, Sadao
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p. 1937 - 1940
(2007/10/02)
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- Transacetalation: a convenient, nonaqueous method for effecting the deprotection of isopropylidene and benzylidene derivatives of sugars
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Sugar isopropylidene and benzylidene derivatives can be readily deprotected under nonaqueous conditions by treatment of a dichloromethane solution of the protected sugar with an excess of a sacrificial glycol in the presence of a catalytic amount of p-toluenesulfonic acid.The reaction is conveniently monitored by GLC, and the fully or partially deprotected product precipitates from solution.
- Andrews, Mark A.,Gould, George L.
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p. 141 - 148
(2007/10/02)
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- Stereoselective and Rapid Synthesis of D-Mannose
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During the course of our studies on labeling reactions with tracer elements, a new rapid and stereoselective synthesis of D-mannose was found.Reaction of 2,3:4,5-di-O-isopropylidene-D-arabinose with trimethylsilylcyanide and zinc iodide in dichloromethane followed by reduction gave D-mannose in good yield.
- Nishimura, Shintaro,Hayashi, Nobuyoshi
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p. 1815 - 1818
(2007/10/02)
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- Metal-mediated decarbonylation and dehydration of ketose sugars
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Ketose sugars can be decarbonylated and/or dehydrated by the action of certain metal complexes. Fructose reacts with 1 equiv of RhCl(PPh3)3 (1) in N-methyl-2-pyrrolidinone (NMP) at 130°C to give furfuryl alcohol, Rh(CO)Cl(PPh3)2 (2), and a small amount of 1-deoxyerythritol. 1,3-Dihydroxyacetone consumes 2 equiv of 1, giving methane and ca. 2 mol of 2. With manno-2-heptulose the primary product is 2,7-anhydromanno-2-heptulopyranose. The mechanisms of these unusual reactions have been studied by using 13C-labeling experiments and model reactions employing Pd(II) and HCl. Attempts to make the reactions catalytic using [Rh(Ph2PCH2CH2CH2PPh 2)2]+[BF4]- in place of 1 were not successful. The use of NMP as a solvent offers some advantages in the acid-catalyzed synthesis of certain carbohydrate dehydration products, as exemplified by the conversion of manno-2-heptulose to its 2,7-anhydride and of 2-deoxyglucose to 1-(2-furanyl)-1,2-ethanediol.
- Andrews, Mark A.
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p. 2703 - 2708
(2008/10/08)
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- Structure of the capsular polysaccharide of Klebsiella serotype K40.
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The capsular polysaccharide from Klebsiella Serotype K40 contains D-galactose, D-mannose, L-rhamnose, and D-glucuronic acid in the ratios of 4:1:1:1. Methylation analysis of the native and carboxyl-reduced polysaccharide provided information about the glycosidic linkages in the repeating unit. Degradation of the permethylated polymer with base established the identity of the sugar unit preceding the glycosyluronic acid residue. The modes of linkages of different sugar residues were further confirmed by Smith degradation and partial hydrolysis of the K40 polysaccharide. The anomeric configurations of the different sugar residues were determined by oxidation of the peracetylated native and carboxyl-reduced polysaccharide with chromium trioxide. Based on all of these results, the heptasaccharide structure 1 was assigned to the repeating unit of the K40 polysaccharide. (Formula: see text)
- Ray,Roy,Roy
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- NEW MECHANISTIC PROPOSAL FOR SOME HEPTAMOLYBDATE-ION-CATALYZED ISOMERIZATIONS
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Heptamolybdate-ion(HM)-catalyzed C(2) epimerization of D-glucose and racemization of D-glyceraldehyde proceed with comparable rates and activation parameters; HM catalyzes the isomerisation of glucal and galactal triacetates as well.For all of the above transformations, a common, new mechanism is proposed that invokes stabilization of 3-oxa-allylic cation species by the central Mo(VI) atom.
- Klaic, Branimir,Raza, Zlata,Sankovic, Mauricio,Sunjic, Vitomir
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- THE STRUCTURAL ELUCIDATION OF THE CAPSULAR POLYSACCHARIDE OF Klebsiella K68
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The structure of the capsular polysaccharide isolated from Klebsiella K68 bacteria has been elucidated by both chemical and spectroscopic methods.The structure is of the "3+1" type, similar in pattern to the structures of the polysaccharides of Klebsiella K11 and K57, having a single branch point on the uronic acid.The polysaccharide is shown to consist of the following repeating unit:
- Dutton, Guy G. S.,Parolis, Haralambos,Parolis, Lesley A. S.
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p. 249 - 260
(2007/10/02)
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