- Molecular-Level Understanding of the Major Fragmentation Mechanisms of Cellulose Fast Pyrolysis: An Experimental Approach Based on Isotopically Labeled Model Compounds
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Evaluation of the feasibility of various mechanisms possibly involved in cellulose fast pyrolysis is challenging. Therefore, selectively 13C-labeled cellotriose, 18O-labeled cellobiose, and 13C- and 18O-doubly-labeled cellobiose were synthesized and subjected to fast pyrolysis in an atmospheric pressure chemical ionization source of a linear quadrupole ion trap/orbitrap mass spectrometer. The initial products were immediately quenched, ionized using ammonium cations, and subsequently analyzed using the mass spectrometer. The loss or retention of isotope labels upon pyrolysis unambiguously revealed three major competing mechanisms - sequential losses of glycolaldehyde/ethenediol molecules from the reducing end (the reducing-end unraveling mechanism), hydroxymethylene-assisted glycosidic bond cleavage (HAGBC mechanism), and Maccoll elimination. Important discoveries include the following: (1) Reducing-end unraveling is the predominant mechanism occurring at the reducing end; (2) Maccoll elimination facilitates the cleaving of aglyconic bonds, and it is the mechanism leading to formation of reducing carbohydrates; 3) HAGBC occurs for glycosides but not at the reducing end of cellodextrins; 4) HAGBC and water loss are the predominant reactions for fast pyrolysis of 1,6-anhydrocellodextrins; and 5) HAGBC can proceed after reducing-end unraveling but unraveling does not occur once the HAGBC reaction pathway is initiated. Moreover, hydrolysis was conclusively ruled out for fast pyrolysis of cellobiose, cellotriose, and 1,6-anhydrocellodextrins up to cellotetraosan. No radical reactions were observed.
- Yu, Zaikuan J.,Easton, McKay W.,Murria, Priya,Xu, Lan,DIng, Duanchen,Jiang, Yuan,Zhang, Jifa,Kentt?maa, Hilkka I.
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p. 7037 - 7050
(2019/06/14)
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- Chemical synthesis of diglucosyl diacylglycerols utilizing glycosyl donors with stereodirecting cyclic silyl protective groups
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Chemical syntheses of the bacterial diglucosyl diacylglycerols 1-heptadecanoyl-2-pentadecanoyl-3-O-[6-O-(β-d-glucopyranosyl)-β-d-glucopyranosyl]-sn-glycerol and 1-(cis-13-octadecenoyl)-2-palmitoyl-3-O-[2-O-(α-d-glucopyranosyl)-α-d-glucopyranosyl]-sn-glycerol are described. The syntheses feature the stereoselective construction of glycosidic linkages in glycosylation reaction by utilizing glycosyl donors with stereodirecting cyclic silyl protective groups. The 1,1,3,3-tetraisopropyldisiloxane-1,3-diyl (TIPDS) group was used for formation of the β-glycosidic linkage, while the di-tert-butylsilylene (DTBS) group was used for α-linkage formation. The silyl protective groups were chemoselectively cleavable without affecting acyl functionalities on the glycerol moiety and proved effective for the synthesis of diacylglycoglycerolipids.
- Takato, Koichi,Kurita, Motoki,Yagami, Nahoko,Tanaka, Hide-Nori,Ando, Hiromune,Imamura, Akihiro,Ishida, Hideharu
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- 4,6- O-Pyruvyl Ketal Modified N-Acetylmannosamine of the Secondary Cell Wall Polysaccharide of Bacillus anthracis Is the Anchoring Residue for Its Surface Layer Proteins
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The secondary cell wall polysaccharide (SCWP) of Bacillus anthracis plays a key role in the organization of the cell envelope of vegetative cells and is intimately involved in host-guest interactions. Genetic studies have indicated that it anchors S-layer and S-layer-associated proteins, which are involved in multiple vital biological functions, to the cell surface of B. anthracis. Phenotypic observations indicate that specific functional groups of the terminal unit of SCWP, including 4,6-O-pyruvyl ketal and acetyl esters, are important for binding of these proteins. These observations are based on genetic manipulations and have not been corroborated by direct binding studies. To address this issue, a synthetic strategy was developed that could provide a range of pyruvylated oligosaccharides derived from B. anthracis SCWP bearing base-labile acetyl esters and free amino groups. The resulting oligosaccharides were used in binding studies with a panel of S-layer and S-layer-associated proteins, which identified structural features of SCWP important for binding. A single pyruvylated ManNAc monosaccharide exhibited strong binding to all proteins, making it a promising structure for S-layer protein manipulation. The acetyl esters and free amine of SCWP did not significantly impact binding, and this observation is contrary to a proposed model in which SCWP acetylation is a prerequisite for association of some but not all S-layer and S-layer-associated proteins.
- Chapman, Robert N.,Liu, Lin,Boons, Geert-Jan
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supporting information
p. 17079 - 17085
(2018/12/14)
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- Synthesis, biological evaluation and structure-activity relationship studies of hederacolchiside E and its derivatives as potential anti-Alzheimer agents
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Inspired by the previously reported neuroprotective activity of hederacolchiside E (1), we synthesized hederacolchiside E for the first time along with eleven of its derivatives. The neuroprotective effects of these compounds were further evaluated agains
- Li, Hui-ning,Liu, Yang,Zhang, Zuo-peng,Wang, Zhi-peng,Hao, Jing-zheng,Li, Feng-ran,Fan, Zhan-fang,Zou, Li-bo,Cheng, Mao-sheng
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p. 376 - 389
(2017/12/07)
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- 2,4,6-Trichloro-1,3,5-triazine (TCT) mediated one-pot sequential functionalisation of glycosides for the generation of orthogonally protected monosaccharide building blocks
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Orthogonally protected monosaccharide building blocks have been prepared using TCT in a one-pot multicomponent transformation. The process involves successive steps of arylidene acetalation, esterification and regioselective reductive acetal cleavage. High regioselectivity, scope for using a broad range of substrates, functional group tolerance, mild reaction conditions, easy handling process and wide application range are a few advantages of the current process.
- Tatina, Madhubabu,Yousuf, Syed Khalid,Mukherjee, Debaraj
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supporting information; experimental part
p. 5357 - 5360
(2012/07/30)
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- Efficient acylation and sulfation of carbohydrates using sulfamic acid, a mild, eco-friendly catalyst under organic solvent-free conditions
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A fast and efficient acylation of carbohydrate derivatives and free sugars using a stoichiometric quantity of acylating agents in the presence of sulfamic acid, an environmentally benign catalyst, under organic solvent-free conditions is reported. Excellent yields in the selective acylation and sulfation of carbohydrate derivatives have also been achieved using sulfamic acid as the catalyst. The reaction is fast and the yields were excellent.
- Santra, Abhishek,Guchhait, Goutam,Misra, Anup Kumar
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experimental part
p. 1345 - 1351
(2011/06/26)
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- Acylation of carbohydrates over Al2O3: Preparation of partially and fully acylated carbohydrate derivatives and acetylated glycosyl chlorides
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Selective and per-O-acylation of carbohydrate derivatives using acyl chlorides and Al2O3, a solid support reagent, is reported. This protocol does not require the addition of any base or activator. This methodology has been further extended to the selective acylation of carbohydrate diols and the one-pot preparation of acetylated glycosyl chlorides direct from free reducing sugars. The yields obtained in most of the cases are excellent.
- Tiwari, Pallavi,Misra, Anup Kumar
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p. 339 - 350
(2007/10/03)
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- A facile protocol for direct conversion of unprotected sugars into phenyl 4,6-O-benzylidene-per-O-acetylated-1,2-trans-thioglycosides
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A short and practical methodology for conversion of unprotected D-glucose, maltose, cellobiose and lactose into the corresponding phenyl 4,6-O-benzylidine-per-O-acetylated-1,2-trans-thioglycosides is described. The protocol is based on the execution of five reaction steps (bromoacetylation, thiophenolysis under phase transfer catalysis conditions, deacetylation, benzylidenation and acetylation) in one continuous procedure and provides a fast access to the title compounds as pure crystalline products without chromatographic purification.
- Larsen, Kim,Olsen, Carl Erik,Motawia, Mohammed Saddik
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p. 199 - 202
(2007/10/03)
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- Chemical synthesis of 6'-α-maltosyl-maltotriose, a branched oligosaccharide representing the branch point of starch
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Chemical synthesis of the branched pentasaccharide 6'-α-maltosyl-maltotriose (15) is reported, based on the use of one synthon as a glycosyl acceptor and another synthon as a glycosyl donor. The synthon used as glycosyl acceptor was phenyl 2,3,6-tri-O-benzyl-1-thio-β-D-glucopyranoside (7) and was synthesized from D-glucose with phenyl 2,3-di-O-acetyl-4,6-O-benzylidene-1-thio-β-D-glucopyranoside and phenyl 2,3-di-O-benzyl-4,6-O-benzylidene-1-thio-β-D-glucopyranoside as key intermediates. The synthon used as glycosyl donor was O-(2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl)-(1 → 4)-O-(2,3,6-tri-O-benzyl-α-D-glucopyranosyl)-(1 → 6)-O-[(2,3,4,6-tetra-O-benzylα-D-glucopyranosyl)-(1 → 4)]-2,3-di-O-benzyl-α,β-D-glucopyranosyl trichloroacetimidate (12) and was synthesized from phenyl O-(2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl)-(1 → 4)-O-(2,3,6-tri-O-benzyl-α-D-glucopyranosyl)-(1 → 6)-O-[(2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl)(1 → 4)]-2,3-di-O-acetyl-1-thio-β-D-glucopyranoside with O-(2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl)-(1 → 4)-O-(2,3,6-tri-O-benzyl-α-D-glucopyranosyl)-(1 → 6)-O-[(2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl)-(1 → 4)]-2,3-di-O-benzyl-D-glucopyranose as an intermediate. Condensation of compounds 7 and 12 followed by removal of the phenylthio group and debenzylation provided the branched pentasaccharide 15. Alternatively, the branched pentasaccharide was produced from amylopectin by consecutive alpha- and beta-amylase treatments and purified by chromatography. The identity of the products obtained by chemical synthesis and enzymatic hydrolysis is documented by 1H and 13C NMR spectra.
- Motawia,Olsen,Enevoldsen,Marcussen,Moller
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p. 109 - 123
(2007/10/02)
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- SmI2-promoted chemistry at the anomeric center of carbohydrates. Reductive formation and reaction of glycosyl samarium (III) reagents
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Reaction of 3,4,6-tri-O-benzyl-2-deoxy-α-D-arabino-hexopyranosyl chloride at room temperature with the efficient single electron transfer system of SmI2-THF-HMPA, in the presence of cyclopentanone (Barbier conditions) gave selectively the corresponding α-C-glycoside in 70percent yield.It is postulated that the reactive transient intermediate is a chiral anomeric organosamarium (III) species.Lower yields were obtained in the presence of aldehydes, such as n-butanal or isobutanal.It is also demonstrated that glycosyl phenyl sulfones undergo reductive samariation. 2,3,4,6-Tetra-O-benzyl-β-D-glucopyranosyl phenyl sulfone reacted with cyclopentanone, in the presence of SmI2-THF-HMPA, to give the corresponding β-C-glycoside selectively in 25percent yield, together with the elimination product (40percent).When the protecting group at C-2 was an acetate, a very fast β-elimination of the organosamarium intermediate occurred to give a practically quantitative yield of a substituted glycal.This work constitutes the first application of samarium(II) iodide to the reductive metallation of the anomeric center of carbohydrates.Key words: samarium diiodide / sulfones / carbohydrates / glycals / C-glycosides
- Pouilly, P. de,Chenede, A.,Mallet, J.-M.,Sinay, P.
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p. 256 - 265
(2007/10/02)
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