- 1,2-Acyloxyl Migration in Pyranosyl Radicals
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Tetra-O-acetylgalactosyl radical (5) and tetra-O-acetylglucosyl radical (10) undergo a 1,2-migration of acetoxyl groups to the corresponding 2-deoxytetra-O-acetylpyranosan-2-yl radicals.The activation parameters for the rearrangement of tetra-O-acetylgalactosyl radical, as determined by ESR spectroscopy, are ΔH(excit.) = 12.2 +/- 0.3 kcal/mol and ΔS(excit.) = -6.7 +/- 1.0 eu.Labeling studies with 18 O support a five-membered cyclic transition state for the rearrangement with exchange of the oxygen atoms of the carboxy group.The driving force for the rearrangement, which is unfavorable in terms of the stability of the radical centers, derives from the gain in anomeric stabilization of the product radical.
- Korth, Hans-Gert,Sustmann, Reiner,Groeninger, Kay Stefan,Leisung, Michael,Giese, Bernd
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Read Online
- Pachymoside A - A novel glycolipid isolated from the marine sponge Pachymatisma johnstonia
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Crude extracts of the North Sea marine sponge Pachymatisma johnstonia showed promising activity in a new assay for inhibitors of bacterial type III secretion. Bioassay-guided fractionation resulted in the isolation of the pachymosides, a new family of sponge glycolipids. A major part of the structural diversity in this family of glycolipids involves increasing degrees of acetylation and differing positions of acetylation on a common pachymoside glycolipid template. All of the metabolites with these variations in acetylation pattern were converted into the same peracetylpachymoside methyl ester (2) for purification and spectroscopic analysis. Pachymoside A (1) is the component of the mixture that has natural acetylation at the eight galactose hydroxyls and at the C-6 hydroxyls of glucose-B and glucose-D. Chemical degradation and transformation in conjunction with extensive analysis of 800 MHz NMR data was used to elucidate the structure of pachymoside A (1).
- Warabi, Kaoru,Zimmerman, William T.,Shen, Jingkai,Gauthier, Annick,Robertson, Marilyn,Finlay, B. Brett,Van Soest, Rob,Andersen, Raymond J.
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- Probing the Transition States of Four Glucoside Hydrolyses with 13C Kinetic Isotope Effects Measured at Natural Abundance by NMR Spectroscopy
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Kinetic isotope effects (KIEs) were measured for methyl glucoside (4) hydrolysis on unlabeled material by NMR. Twenty-eight 13C KIEs were measured on the acid-catalyzed hydrolysis of α-4 and β-4, as well as enzymatic hydrolyses with yeast α-glucosidase and almond β-glucosidase. The 1-13C KIEs on the acid-catalyzed reactions of α-4 and β-4, 1.007(2) and 1.010(6), respectively, were in excellent agreement with the previously reported values (1.007(1), 1.011(2): Bennet and Sinnott, J. Am. Chem. Soc. 1986, 108, 7287). Transition state analysis of the acid-catalyzed reactions using the 13C KIEs, along with the previously reported 2H KIEs, confirmed that both reactions proceed with a stepwise DN*AN mechanism and showed that the glucosyl oxocarbenium ion intermediate exists in an E3 sofa or 4H3 half-chair conformation. 13C KIEs showed that the α-glucosidase reaction also proceeded through a D N*AN mechanism, with a 1-13C KIE of 1.010(4). The secondary 13C KIEs showed evidence of distortions in the glucosyl ring at the transition state. For the β-glucosidase-catalyzed reaction, the 1-13C KIE of 1.032(1) demonstrated a concerted A NDN mechanism. The pattern of secondary 13C KIEs was similar to the acid-catalyzed reaction, showing no signs of distortion. KIE measurement at natural abundance makes it possible to determine KIEs much more quickly than previously, both by increasing the speed of KIE measurement and by obviating the need for synthesis of isotopically labeled compounds.
- Lee, Jason K.,Bain, Alex D.,Berti, Paul J.
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- General Strategy for the Synthesis of Rare Sugars via Ru(II)-Catalyzed and Boron-Mediated Selective Epimerization of 1,2- trans-Diols to 1,2- cis-Diols
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Human glycans are primarily composed of nine common sugar building blocks. On the other hand, several hundred monosaccharides have been discovered in bacteria and most of them are not readily available. The ability to access these rare sugars and the corresponding glycoconjugates can facilitate the studies of various fundamentally important biological processes in bacteria, including interactions between microbiota and the human host. Many rare sugars also exist in a variety of natural products and pharmaceutical reagents with significant biological activities. Although several methods have been developed for the synthesis of rare monosaccharides, most of them involve lengthy steps. Herein, we report an efficient and general strategy that can provide access to rare sugars from commercially available common monosaccharides via a one-step Ru(II)-catalyzed and boron-mediated selective epimerization of 1,2-trans-diols to 1,2-cis-diols. The formation of boronate esters drives the equilibrium toward 1,2-cis-diol products, which can be immediately used for further selective functionalization and glycosylation. The utility of this strategy was demonstrated by the efficient construction of glycoside skeletons in natural products or bioactive compounds.
- Li, Xiaolei,Tang, Weiping,Wu, Jicheng
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p. 3727 - 3736
(2022/03/02)
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- Structure of the unusual Sinorhizobium fredii HH103 lipopolysaccharide and its role in symbiosis
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Rhizobia are soil bacteria that form important symbiotic associations with legumes, and rhizobial surface polysaccharides, such as K-antigen polysaccharide (KPS) and lipopolysaccharide (LPS), might be important for symbiosis. Previously, we obtained a mutant of Sinorhizobium fredii HH103, rkpA, that does not produce KPS, a homopolysaccharide of a pseudaminic acid derivative, but whose LPS electrophoretic profile was indistinguishable from that of the WT strain. We also previously demonstrated that the HH103 rkpLMNOPQ operon is responsible for 5-acetamido-3,5,7,9-tetradeoxy-7-(3-hydroxybutyramido)-L-glyc-ero-L-manno-nonulosonic acid [Pse5NAc7(3OHBu)] production and is involved in HH103 KPS and LPS biosynthesis and that an HH103 rkpM mutant cannot produce KPS and displays an altered LPS structure. Here, we analyzed the LPS structure of HH103 rkpA, focusing on the carbohydrate portion, and found that it contains a highly heterogeneous lipid A and a peculiar core oligosaccharide composed of an unusually high number of hexuronic acids containing b-configured Pse5NAc7(3OHBu). This pseudaminic acid derivative, in its a-configuration, was the only structural component of the S. fredii HH103 KPS and, to the best of our knowledge, has never been reported from any other rhizobial LPS. We also show that Pse5NAc7(3OHBu) is the complete or partial epitope for a mAb, NB6-228.22, that can recognize the HH103 LPS, but not those of most of the S. fredii strains tested here. We also show that the LPS from HH103 rkpM is identical to that of HH103 rkpA but devoid of any Pse5NAc7(3OHBu) residues. Notably, this rkpM mutant was severely impaired in symbiosis with its host, Macroptilium atropurpureum.
- Di Lorenzo, Flaviana,Speciale, Immacolata,Silipo, Alba,Alías-Villegas, Cynthia,Acosta-Jurado, Sebastián,Rodríguez-Carvajal, Miguel-ángel,Dardanelli, Marta S.,Palmigiano, Angelo,Garozzo, Domenico,Ruiz-Sainz, José-Enrique,Molinaro, Antonio,Vinardell, José-María
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p. 10969 - 10987
(2021/01/07)
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- Direct dehydrative glycosylation catalyzed by diphenylammonium triflate
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Methods for direct dehydrative glycosylations of carbohydrate hemiacetals catalyzed by diphenylammonium triflate under microwave irradiation are described. Both armed and disarmed glycosyl-C1-hemiacetal donors were efficiently glycosylated in moderate to excellent yields without the need for any drying agents and stoichiometric additives. This method has been successfully applied to a solid-phase glycosylation.
- Hsu, Mei-Yuan,Lam, Sarah,Lin, Mei-Huei,Lin, Su-Ching,Wang, Cheng-Chung,Wu, Chia-Hui
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supporting information
(2020/03/13)
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- Phosphotungstic acid as a novel acidic catalyst for carbohydrate protection and glycosylation
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This work demonstrates the utilization of phosphotungstic acid (PTA) as a novel acidic catalyst for carbohydrate reactions, such as per-O-acetylation, regioselective O-4,6 benzylidene acetal formation, regioselective O-4 ring-opening, and glycosylation. These reactions are basic and salient during the synthesis of carbohydrate-based bioactive oligomers. Phosphotungstic acid's high acidity and eco-friendly character make it a tempting alternative to corrosive homogeneous acids. The various homogenous acid catalysts were replaced by the phosphotungstic acid solely for different carbohydrate reactions. It can be widely used as a catalyst for organic reactions as it is thermally stable and easy to handle. In our work, the reactions are operated smoothly under ambient conditions; the temperature varies from 0 °C to room temperature. Good to excellent yields were obtained in all four kinds of reactions.
- Chen, Jyun-Siao,Sankar, Arumugam,Lin, Yi-Jyun,Huang, Po-Hsun,Liao, Chih-Hsiang,Wu, Shen-Shen,Wu, Hsin-Ru,Luo, Shun-Yuan
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p. 33853 - 33862
(2019/11/11)
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- ACYLATED ACTIVE AGENTS AND METHODS OF THEIR USE FOR THE TREATMENT OF AUTOIMMUNE DISORDERS
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Disclosed herein are acylated active agents (e.g., acylated catechin polyphenols, acylated carotenoids, acylated mesalamines, acylated sugars, acylated shikimic acids, acylated ellagic acid, acylated ellagic acid analogue, and acylated hydroxybenzoic acids), active agent combinations (e.g., with a second agent that is a fatty acid) and methods of their use, e.g., for modulating an autoimmunity marker or for treating an autoimmune disorder.
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Page/Page column 157; 128
(2019/12/28)
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- Structural properties of D-mannopyranosyl rings containing O-Acetyl side-chains
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The crystal structures of 1,2,3,4,6-penta-O-Acetyl--d-mannopyranose, C16H22O11, and 2,3,4,6-Tetra-O-Acetyl--d-mannopyranosyl-(1.2)-3,4,6-Tri-O-Acetyl--d-mannopyranosyl-( 1.3)-1,2,4,6-Tetra-O-Acetyl--d-mannopyranose, C40H54O27, were determined and compared to those of methyl 2,3,4,6-Tetra-O-Acetyl--d-mannopyranoside, methyl -d-mannopyranoside andmethyl -d-mannopyranosyl-(1.2)--d-mannopyranoside to evaluate the effects of O-Acetylation on bond lengths, bond angles and torsion angles. In general, O-Acetylation exerts little effect on the exo-and endocyclic C-C and endocyclic C-O bond lengths, but the exocyclic C-O bonds involved in O-Acetylation are lengthened by -0.02 A ° . The conformation of the O-Acetyl side-chains is highly conserved, with the carbonyl O atom either eclipsing the H atom attached to a 2-Alcoholic C atom or bisecting the H-C-H bond angle of a 1-Alcoholic C atom. Of the two C-O bonds that determine O-Acetyl side-chain conformation, that involving the alcoholic C atom exhibits greater rotational variability than that involving the carbonyl C atom. These findings are in good agreement with recent solution NMR studies of O-Acetyl side-chain conformations in saccharides. Experimental evidence was also obtained to confirm density functional theory (DFT) predictions of C-O and O-H bond-length behavior in a C-O-H fragment involved in hydrogen bonding.
- Turney, Toby,Zhang, Wenhui,Oliver, Allen G.,Serianni, Anthony S.
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p. 1166 - 1174
(2019/08/13)
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- Calcium hypophosphite mediated deiodination in water: Mechanistic insights and applications in large scale syntheses of d-quinovose and d-rhamnose
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The inorganic calcium hypophosphite was found to be a cheap, non-toxic, water-soluble and environmentally friendly reducing reagent for radical deiodination in water. Thorough mechanism studies revealed that calcium hypophosphite was oxidized to water insoluble calcium phosphite which was the major co-product of the deiodination reaction. Based on this observation, a practical synthesis of rare d-quinovose and d-rhamnose from cheap and commercially available materials on a hundred-mmol scale was reported.
- Song, Zejin,Meng, Lingkui,Xiao, Ying,Zhao, Xiang,Fang, Jing,Zeng, Jing,Wan, Qian
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supporting information
p. 1122 - 1127
(2019/03/12)
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- Antimycobacterial 1,4-napthoquinone natural products from Moneses uniflora
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A new 1,4-naphthoquinone derivative, 5,8-dihydro-3-hydroxychimaphilin (4) and five known compounds (1, 2 and 5–7) were isolated from an extract of the Canadian medicinal plant Moneses uniflora that significantly inhibited the growth of Mycobacterium tuberculosis H37Ra. The structure of 4 was established through analysis of NMR and MS data and the absolute configuration of the glycone of 5 was determined by chemical transformation and comparison with standards prepared from D- and L-glucose. All compounds isolated were screened against Mycobacterium tuberculosis (H37Ra) and the mammalian HEK 293 cell line and, with the exception of compounds 5 and 7, exhibited marked selectivity in their bioactivity: Compound 1 exhibited potent antimycobacterial activity (IC50 of 5.4 μM) and moderate cytotoxicity (IC50 of 30 μM); compounds 2, 4 and 6 showed moderate antimycobacterial activity (IC50 values from 28 to 47 μM) without affecting the viability of mammalian cells; compound 5 displayed moderate activity in both assays (IC50 values of 44 and 55 μM respectively); and compound 7 was not active in either assay. These data suggest that the Moneses napthaquinone derivatives elicit biological responses in mycobacterial and mammalian cells through disparate modes of action that warrant further investigation.
- Li, Haoxin,Bos, Allyson,Jean, Stéphanie,Webster, Duncan,Robichaud, Gilles A.,Johnson, John A.,Gray, Christopher A.
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p. 229 - 233
(2018/08/21)
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- Sequential Dy(OTf)3-Catalyzed Solvent-Free Per-O-Acetylation and Regioselective Anomeric De-O-Acetylation of Carbohydrates
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Dysprosium(III) trifluoromethanesulfonate-catalyzed per-O-acetylation and regioselective anomeric de-O-acetylation of carbohydrates can be tuned by adjusting the reaction medium. In this study, the per-O-acetylation of unprotected sugars by using a near-stoichiometric amount of acetic anhydride under solvent-free conditions resulted in the exclusive formation of acetylated saccharides as anomeric mixtures, whereas anomeric de-O-acetylation in methanol resulted in a moderate-to-excellent yield. Reactions with various unprotected monosaccharides or disaccharides followed by a semi-one-pot sequential conversion into the corresponding acetylated glycosyl hemiacetal also resulted in high yields. Furthermore, the obtained hemiacetals could be successfully transformed into trichloroimidates after Dy(OTf)3-catalyzed glycosylation.
- Yan, Yi-Ling,Guo, Jiun-Rung,Liang, Chien-Fu
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p. 2471 - 2479
(2017/09/06)
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- Highly Regioselective Monoacylation of Unprotected Glucopyranoside Using Transient Directing-Protecting Groups
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The regioselective functionalization of monosaccharides is notoriously achieved using metal catalysis, lengthy synthetic strategies requiring protection/deprotection, various enzymes, or other methods that target cis-diols (and thus cannot be used with glucopyranose derivatives), In this paper, we report a new method using selected boronic acids as temporary protecting groups, and describe its application to the regioselective functionalization of methyl α-d-glucopyranoside, the most difficult monosaccharide to functionalize regioselectively. Generally, reactions of glucopyranosides may lead to a plethora of mono- and polyfunctionalized derivatives, yet our method gave the 3-O-acetylated, 2-O-benzoylated, and 2-O-pivaloylated derivatives of methyl α-d-glucopyranoside as major products. We focused on the use of recyclable and green temporary protecting groups (in a one-pot reaction) and on the modulation of the intramolecular hydrogen-bonding network using selected arylboronic acids. A complete scalable procedure leading to a single regioisomer from unprotected methyl α-d-glucopyranoside is presented.
- Rocheleau, Sylvain,Pottel, Joshua,Huski?, Igor,Moitessier, Nicolas
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p. 646 - 656
(2017/02/05)
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- DMAP-based flexible polymer networks formed via Heck coupling as efficient heterogeneous organocatalysts
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Two DMAP-based flexible polymer networks TPB-DMAP and TPA-DMAP have been successfully synthesized via palladium catalyzed Heck cross-coupling. The structures of these polymers were confirmed by solid state 13C CP/MAS and Fourier transform infrared spectroscopy (FTIR). Although both polymers have negligible surface areas, they exhibit excellent catalytic efficiency for the acylation of 1-phenylethanol with acetic anhydride due to their good swelling capacities. Utilized as a typical catalyst, the polymer TPA-DMAP shows high activities for acylation of a variety of alcohols to the corresponding esters. Moreover, the catalyst can be recycled at least ten times without obvious loss of catalytic activity.
- Xu, Wei,Xia, Wu,Guan, Yukun,Wang, Yiming,Lu, Cuifen,Yang, Guichun,Nie, Junqi,Chen, Zuxing
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- Tunable microwave-assisted method for the solvent-free and catalyst-free peracetylation of natural products
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Background: The peracetylation is a simple chemical modification that can be used to enhance the bioavailability of hydrophilic products and to obtain safe and stable pro-drugs. Results: A totally green, solvent-free and catalyst-free microwave (MW)-assisted method for peracetylation of natural products such as oleuropein, alpha-hederin, quercetin and rutin is presented. By simply tuning the MW heating program, polyols with chemical diverse -OH groups or thermolabile functionalities can be peracetylated to improve the biological activity without degradation of the natural starting molecules. An evaluation of the process greenness was performed. Conclusion: The method is potentially universally applicable for green acetylation of hydrophilic biological molecules, potentially easily scalable for industrial applications, including pharmaceutical, cosmetic and food industry.
- Oliverio, Manuela,Costanzo, Paola,Nardi, Monica,Calandruccio, Carla,Salerno, Raffaele,Procopio, Antonio
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supporting information
p. 2222 - 2233
(2016/11/17)
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- Tetranuclear zinc cluster: A dual purpose catalyst for per-: O -acetylation and de- O -acetylation of carbohydrates
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The trifluoroacetic acid adduct of tetranuclear zinc cluster Zn4(OCOCF3)6O catalysis in per-O-acetylation and de-O-acetylation of carbohydrates at 70 °C can be tuned by adjusting the reaction medium. Per-O-acetylation of hexopyranoses with a near stoichiometric amount of acetic anhydride in toluene resulted in the exclusive formation of pyranosyl products as an anomeric mixture, whereas de-O-acetylation of acetates occurred in methanol in high yields. In the latter, methanol acts as both nucleophile and solvent, and the reaction conditions were compatible to acid- and base-sensitive groups and amino acid derivatives.
- Lin, Ting-Wei,Adak, Avijit K.,Lin, Hong-Jyune,Das, Anindya,Hsiao, Wei-Chen,Kuan, Ting-Chun,Lin, Chun-Cheng
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p. 58749 - 58754
(2016/07/07)
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- Conversion of β-glycopyranoside to α-glycopyranoside by photo-activated radical reaction
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By using carbon tetrachloride as the chloride radical and boron trifluoride etherate as the Lewis acid, the halogen-light-activated anomeric inversion of glycoside was achieved. This reaction is a novel guide to invert the glycosidic bond from a β-anomer to an α-anomer.
- Lai, Yu-Chen,Luo, Chin-Hung,Chou, Hsin-Chun,Yang, Cheng-Jhang,Lu, Le,Chen, Chien-Sheng
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supporting information
p. 2474 - 2477
(2016/05/24)
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- Cu(ClO4)2·6H2O catalyzed solvent free per-O-acetylation and sequential one-pot conversions of sugars to thioglycosides
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The solvent free per-O-acetylation of various reducing and non-reducing sugars has been carried out using stoichiometric amounts of acetic anhydride and copper(ii) perchlorate hexahydrate as the catalyst. The reactions with various reducing monosaccharides have also been followed by a one-pot sequential conversion to the corresponding thioglycosides in high yields. This journal is
- Chatterjee, Debnath,Paul, Abhijit,Rajkamal,Yadav, Somnath
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p. 29669 - 29674
(2015/05/20)
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- Acyl transfer reactions of carbohydrates, alcohols, phenols, thiols and thiophenols under green reaction conditions
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Acyl transfer reactions of various carbohydrates, alcohols, phenols, thiols and thiophenols were achieved at room temperature in high yields and catalytic efficiency in the presence of methane sulfonic acid, a green organic acid, under solvent-free conditions over short time periods. The method is mild enough to allow acid labile substituents such as isopropylidene acetals and trityl ethers on the reacting substrates to be left completely unaffected. Esterification of free mono- and dicarboxylic acids such as acetic acid, cinnamic acid, sialic acid and tartaric acid with alcohols such as menthol, ethanol, methanol or propylene glycol has also been achieved efficiently at room temperature. A comparative study of the method with the silica-sulfuric acid is also reported.
- Giri, Santosh Kumar,Kartha, K. P. Ravindranathan
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p. 11687 - 11696
(2015/02/19)
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- Three Solvent-Free Catalytic Approaches to the Acetal Functionalization of Carbohydrates and Their Applicability to One-Pot Generation of Orthogonally Protected Building Blocks
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Three alternative protocols were developed to carry out the selective installation of acetal groups on carbohydrates and polyols under mildly acidic, solvent-free conditions. One protocol is based on a diol/aldehyde condensation at room temperature, with an acetolysis process serving for the activation of the carbonyl component. A second approach is based on an orthoester-mediated activation of the carbonyl component at high temperature. The third protocol is instead entailing a transacetalation mechanism. Combination of these methods allows a wide set of acetal-protected building blocks to be accessed in short times under very simple experimental conditions working under air. The scope of the latter two approaches was also extended to unusual one-pot synthetic sequences leading to concomitant Fischer glycosidation/acetal protection of reducing sugars.
- Traboni, Serena,Bedini, Emiliano,Giordano, Maddalena,Iadonisi, Alfonso
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p. 3562 - 3572
(2016/01/25)
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- Mode of alkylation of alcohols with O-cyclopropylmethyl trichloroacetimidate and O-cyclobutyl trichloroacetimidate
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Acid promoted alkylation of hydroxy group containing acceptors 3-14 with O-cyclopropylmethyl and O-cyclobutyl trichloroacetimidates 1 and 2, respectively, afforded ethers with cyclopropylmethyl, cyclobutyl, and homoallyl residues as a result of the rearrangement of the cation intermediates. The dependence of product formation on acceptor structure is discussed. ARKAT-USA, Inc.
- Ali, Ibrahim A.I.,Zhu, Xiangming,El Ashry, El Sayed H.,Schmidta, Richard R.
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experimental part
p. 35 - 44
(2012/03/09)
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- One-pot oxidation-hydrocyanation sequence coupled to lipase-catalyzed diastereoresolution in the chemoenzymatic synthesis of sugar cyanohydrin esters
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A three-step, one-pot synthesis and diastereoresolution sequence is described in anhydrous toluene starting from methyl α-D-2,3,4-tri-O- acetylgalacto- (1a), -manno- (1b) and -glucopyranosides (1c). The reaction sequence, including consecutive transformations through the aldehyde [PhI(OAc)2, 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)] and cyanohydrin [basic resin or (R)-oxynitrilase] into the (6R)-cyanohydrin ester (lipase) is shown to proceed in a one-pot cascade, except that the basic resin (when used) should be removed before the addition of the enzymatic acylation reagents. We have shown that the effective transformation of 1a (75 % reaction yield) through labile intermediates gives the stable (6R)-cyanohydrin butanoate (85 % de). Further diastereomeric purification by chromatography is possible, although the product is already of high diastereopurity. (6R)-Cyanohydrin esters are obtained through acylation with Burkholderia cepacia lipase. The (6S)-ester (de 99 %) is produced by Candida rugosa lipase when the sequence is started from 1c whereas the other sugar derivatives are less suited to the reaction with lipase. Copyright
- Hietanen, Ari,Kanerva, Liisa T.
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experimental part
p. 2729 - 2737
(2012/07/13)
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- Intramolecular glycosidation by click reaction mediated spacer generation followed by spacer cleavage
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2-O-Propargyl-substituted glycosyl donors and O-(2-azidobenzyl)-substituted acceptors having a vicinal hydroxy group readily underwent the click reaction. Intramolecular glycosidation with N-iodosuccinimide/trifluoromethansulfonic acid as the activating system afforded β-(1-3)- and α-(1-2)-linked disaccharides as part of 14-membered macrocycles. Descriptors for these reactions are proposed that consider the donor and acceptor attachment sites and the stereochemistry of the functional groups. Investigation of the influence of 2-O-linked 1-aryl-1,2,3-triazol-4-ylmethyl groups, as contained in the spacer, on the anomeric selectivity exhibited no anchimeric assistance. In addition, it was shown that the spacer group can be readily cleaved under Birch reduction conditions. The 1,2,3-triazole-forming click reaction was employed to generate glycosyl donor-spacer-acceptor constructs. Upon glycosidation, 14-membered macrocycles were obtained with high anomeric selectivity. Spacer cleavage was performed under Birch reduction conditions. Copyright
- Kumar, Amit,Geng, Yiqun,Schmidt, Richard R.
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supporting information
p. 6846 - 6851
(2013/03/13)
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- Methyl 1,2-orthoesters as useful glycosyl donors in glycosylation reactions: A comparison with n-pent-4-enyl 1,2-orthoesters
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Mannopyranose-derived methyl 1,2-orthoacetates (R = Me) and -benzoates (R = Ph) can function as glycosyl donors - upon BF3·Et 2O activation in CH2Cl2 - in glycosylation reactions with monosaccharide acceptors to afford disaccharides in good yields. In the process, glycosylation is preferred to acid-catalyzed rearrangement leading to methyl mannopyranosides. Methyl 1,2-orthoesters can be also used in regioselective glycosylation protocols with monosaccharide diols, in which they display good regioselectivity. Copyright
- Uriel, Clara,Ventura, Juan,Gomez, Ana M.,Lopez, J. Cristobal,Fraser-Reid, Bert
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experimental part
p. 3122 - 3131
(2012/07/13)
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- Unexpected stereocontrolled access to 1α,1′β-disaccharides from methyl 1,2-ortho esters
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Mannopyranose-derived methyl 1,2-orthoacetates (R = Me) and 1,2-orthobenzoates (R = Ph) undergo stereoselective formation of 1α,1′β-disaccharides, upon treatment with BF 3?Et2O in CH2Cl2, rather than the expected acid-catalyzed reaction leading to methyl glycosides by way of a rearrangement-glycosylation process of the liberated methanol.
- Uriel, Clara,Ventura, Juan,Gomez, Ana M.,Lopez, J. Cristobal,Fraser-Reid, Bert
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experimental part
p. 795 - 800
(2012/03/22)
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- Glycosylation of α-amino acids by sugar acetate donors with InBr 3. Minimally competent Lewis acids
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A simplified method for the preparation of Fmoc-serine and Fmoc-threonine glycosides for use in O-linked glycopeptide synthesis is described. Lewis acids promote glycoside formation, but also promote undesired reactions of the glycoside products. Use of 'minimally competent' Lewis acids such as InBr 3 promotes the desired activation catalytically, and with greatly reduced side products from sugar peracetates.
- Lefever, Mark R.,Szab, Lajos Z.,Anglin, Bobbi,Ferracane, Michael,Hogan, Joanna,Cooney, Lauren,Polt, Robin
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scheme or table
p. 121 - 125
(2012/05/20)
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- 4-(N,N-dimethylamino)pyridine-embedded nanoporous conjugated polymer as a highly active heterogeneous organocatalyst
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We report herein for the first time the incorporation of a versatile organocatalyst, 4-(N,N-dimethylamino)pyridine (DMAP), into the network of a nanoporous conjugated polymer (NCP) by the "bottom-up" approach. The resulting DMAP-NCP material possesses highly concentrated and homogeneously distributed DMAP catalytic sites (2.02 mmol g-1). DMAP-NCP also exhibits enhanced stability and permanent porosity due to the strong covalent linkage and the rigidity of the "bottom-up" monomers. As a result, DMAP-NCP shows excellent catalytic activity in the acylation of alcohols with yields of 92-99 %. The DMAP-NCP catalyst could be easily recovered from the reaction mixture and reused in at least 14 consecutive cycles without measurable loss of activity. Moreover, the catalytic acylation reaction could be performed under neat and continuous-flow conditions for at least 536 h of continuous work with the same catalyst activity. Copyright
- Zhang, Yuan,Zhang, Yong,Sun, Ya Lei,Du, Xin,Shi, Jiao Yi,Wang, Wei,Wang, Wei David
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experimental part
p. 6328 - 6334
(2012/06/18)
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- DABCO: An efficient promoter for the acetylation of carbohydrates and other substances under solvent-free conditions
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A simple, mild and efficient solvent-free method for the acetylation of carbohydrates, and their partially protected derivatives, as well as non-carbohydrate substances in excellent yields in the presence of 1,4-diazabicyclo[2.2.2]octane (DABCO) is described with the advantage of tolerance to various functional groups, short reaction time and ease of product isolation.
- Ch, Ratnasekhar,Tyagi, Mohit,Patil, Premanand Ramrao,Kartha, K.P. Ravindranathan
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experimental part
p. 5841 - 5846
(2011/12/03)
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- Iodine-hexamethyldisilane (HMDS)-mediated anomerization of peracetylated 1,2-trans-linked alkyl and aryl glycosides
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Treatment of peracetylated alkyl and aryl 1,2-trans-glycosides with iodine in the presence of HMDS has been found to result in the anomerization leading to the formation of the respective 1,2-cis-glycosides. In the case of alkyl glycosides with aglycons of short alkyl chain length complete anomerization to the α-glycosides was observed while with those of longer chain length the process was found to be incomplete. The observations have been interpreted mechanistically.
- Malik, Satish,Shah, Krupesh J.,Ravindranathan Kartha
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scheme or table
p. 867 - 871
(2010/06/14)
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- Variations on the SnCl4 and CF3CO2Ag-promoted glycosidation of sugar acetates: a direct, versatile and apparently simple method with either α or β stereocontrol
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Glycosidation of sugar peracetates (d-gluco, d-galacto) with SnCl4 and CF3CO2Ag led to either 1,2-cis-, or 1,2-trans-glycosides, depending primarily on the alcohols used. In particular, 1,2-trans-glycosides, expected from acyl-protected glycosyl donors, were formed in high yields with alcohols sharing specific features such as bulkiness, presence of electron-withdrawing groups or polyethoxy motifs. In contrast, simple alcohols afforded ~1:1 mixtures of 2,3,4,6-tetra-O-acetyl, and 3,4,6-tri-O-acetyl 1,2-cis-glycosides due to anomerization and/or acid-catalyzed fragmentation of 1,2-orthoester intermediates. After reacetylation or deacetylation, acetylated or fully deprotected 1,2-cis-glycosides (α-d-gluco, α-d-galacto) were obtained in ~90% yields by a simple and direct method.
- Xue, Jia Lu,Cecioni, Samy,He, Li,Vidal, Sébastien,Praly, Jean-Pierre
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experimental part
p. 1646 - 1653
(2009/12/24)
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- Indium(III) triflate: A highly efficient catalyst for reactions of sugars
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Indium(III) trifluoromethanesulfonate has been found to be extremely efficient in catalyzing acyl transfer reactions of various carbohydrates and their derivatives. Selective acetolyses of certain benzyl ethers/isopropylidene acetals of sugars have been possible using In(OTf)3 in Ac2O (neat). Reaction of the per-O-acetate of 2-deoxy-2-phthalimido-D-glucose with benzyl mercaptan in the presence of In(OTf)3 led to the formation of the corresponding thioglycoside in high yield. Facile formation and hydrolysis of the isopropylidene and benzylidene acetals of various carbohydrates have also been achieved very efficiently in the presence of In(OTf)3. The results show great promise for In(OTf)3 in synthetic carbohydrate chemistry.
- Giri, Santosh Kumar,Verma, Monika,Kartha, K. P. Ravindranathan
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scheme or table
p. 464 - 478
(2009/04/06)
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- Fe2(SO4)3·xH2O-catalyzed per-O-acetylation of sugars compatible with acid-labile protecting groups adopted in carbohydrate chemistry
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Fully acetylated saccharides are inexpensive and very useful starting materials for the synthesis of many naturally occurring glycosides, oligosaccharides, and glycoconjugates. Ferric sulfate hydrate (Fe2(SO4)3·xH2O) was found to be a valuable Lewis acid promoter in the per-O-acetylation reaction of saccharides with acetic anhydride in 100% of conversion rate and 88-99% yields. Interestingly, the procedure is perfectly compatible with the presence of a variety of acid-labile protecting groups, such as isopropylidene, benzylidene, trityl, and TBDMS groups. The reactions were simply performed by stirring the mixture of a sugar with a slight excessive acetic anhydride in the presence of 2.0 mol % of Fe2(SO4)3·xH2O at rt and the pure products were obtained by a simple dilution of the reaction mixture with dichloromethane and washings with aqueous Na2CO3.
- Shi, Lei,Zhang, Guisheng,Pan, Feng
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p. 2572 - 2575
(2008/09/19)
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- Samarium trifluoromethanesulfonate: An efficient moisture tolerant acylation catalyst under solvent-free condition
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Samarium trifluoromethanesulfonate catalyzed the acylation of phenols, alcohols, thiols, free reducing sugars, and glycosides in excellent yields at ambient temperature under solvent-free condition using stoichiometric amounts of various anhydrides. (Chemical Equation Presented). Copyright Taylor & Francis Group, LLC.
- Roy, Bimalendu,Dasgupta, Somnath,Kumar Rajput, Vishal,Mukhopadhyay, Balaram
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- Tandem epoxidation-alcoholysis or epoxidation-hydrolysis of glycals catalyzed by titanium(IV) isopropoxide or Venturello's phosphotungstate complex
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Venturello's phosphotungstate complex and titanium(IV) isopropoxide [Ti(O-i-Pr)4] were successfully used as catalysts for the epoxidation-alcoholysis of glycals using hydrogen peroxide [H2O 2]. Reaction substrates included a range of variously protected glycals and different alcohols were used as solvents. Ti(O-i-Pr)4 was only effective in methanol as solvent, but gave methyl glycosides in high yields and high selectivities. The Venturello complex proved to be a very versatile and efficient catalyst. Apart from epoxidation-alcoholysis in alcoholic solvents it also showed activity in biphasic conditions to allow for glycosylation of long-chain alcohols and was very effective in the stereoselective dihydroxylation of benzylated glucal.
- Levecque, Pieter,Gammon, David W.,Kinfe, Henok Hadgu,Jacobs, Pierre,De Vos, Dirk,Sels, Bert
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body text
p. 1557 - 1568
(2009/07/10)
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- Indium trichloride promoted stereoselective synthesis of O-glycosides from trialkyl orthoformates
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A novel, highly stereoselective method for O-glycosylation of glycals and glycosylbromides is developed using orthoformates as acceptors in the presence of InCl3 to afford the corresponding O-glycopyranosides in 66-94% yield. Both perbenzyl and peracetyl glycals afford the corresponding 2,3-unsaturated-O-glycosides with high α-selectivity. Stoichiometric amounts of orthoformates are sufficient to bring about this transformation instead of large excesses of alcohols.
- Mukherjee, Debaraj,Yousuf, Syed Khalid,Taneja, Subhash C.
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p. 4944 - 4948
(2008/09/21)
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- Widely useful DMAP-catalyzed esterification under auxiliary base- and solvent-free conditions
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With regard to atom economy and E-factor, catalytic condensation of carboxylic acids with equimolar amounts of alcohols is the most desirable. Although several highly active dehydration catalysts have been reported, more efficient alternatives are still strongly needed because the dehydrative esterification of tertiary alcohols, phenols, acid-sensitive alcohols, amino acids, and hardly soluble alcohols has never proceeded satisfactorily. Here we report new insights into the classical DMAP-catalyzed acylation of alcohols: surprisingly, only a 0.05-2 mol % of DMAP can efficiently promote acylation of alcohols with acid anhydrides under auxiliary base- and solvent-free conditions to give the corresponding esters in high yields. Furthermore, we achieved the recovery and reuse of commercially available polystyrene-supported DMAP without using any solvents. These serendipitous findings provide widely useful and environmentally benign esterification methods, which might be more practical and reliable than catalytic dehydrative condensation methods, in particular, for the less reactive alcohols which hardly condense with carboxylic acid directly.
- Sakakura, Akira,Kawajiri, Kimio,Ohkubo, Takuro,Kosugi, Yuji,Ishihara, Kazuaki
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p. 14775 - 14779
(2008/09/17)
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- Tandem acetalation-acetylation of sugars and related derivatives with enolacetates under solvent-free conditions
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(Chemical Equation Presented) Molecular iodine catalyzes acetalation and acetylation of reducing sugars and sugar glycosides with stoichiometric amounts of enol acetates under solvent-free conditions, thereby facilitating the synthesis of various types of orthogonally protected sugar derivatives in short time and good yields. The outcome of the reaction can be controlled by variation in temperature. Thus at lower temperature, it is possible to obtain the acetonide acetate as a single product whereas peracetate is the major product at higher temperature.
- Mukherjee, Debaraj,Shah, Bhahwal Ali,Gupta, Pankaj,Taneja, Subhash Chandra
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p. 8965 - 8968
(2008/03/12)
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- Mild and efficient method for the cleavage of benzylidene acetals using HClO4-SiO2 and direct conversion of acetals to acetates
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HClO4-SiO2 has been used successfully for the deprotection of benzylidene acetals and the direct conversion of benzylidene acetals to the corresponding di-O-acetates. The reactions are very fast and yields are excellent.
- Agnihotri, Geetanjali,Misra, Anup Kumar
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p. 3653 - 3658
(2007/10/03)
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- Methyltrioxorhenium-catalyzed epoxidation-methanolysis of glycals under homogeneous and heterogeneous conditions
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The efficient and high yielding domino epoxidation-methanolysis of glycals 8-15 has been achieved by oxidation with UHP in MeOH catalyzed by MTO. The products have been conveniently isolated as 2-acetoxy derivatives 16-23a, b by direct acetylation of the crude mixtures. Homogeneous MTO-amine complexes 5-7, heterogeneous poly(4-vinyl-pyridine)/MTO compounds I-III, and microencapsulated polystyrene/MTO systems IV-VII were also tested and demonstrated their effectiveness as catalysts for the oxidation step. The facial diastereoselectivity of the oxidation ranged from satisfactory to excellent depending on the substrate and could be optimized by ample screening of catalysts. Complete conversions of substrates and nearly quantitative yields of products were obtained under environmentally friendly experimental conditions and with the use of simple work-up procedures.
- Goti, Andrea,Cardona, Francesca,Soldaini, Gianluca,Crestini, Claudia,Fiani, Cinzia,Saladino, Raffaele
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p. 476 - 486
(2007/10/03)
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- Efficient acetylation of carbohydrates promoted by imidazole
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An efficient per-O-acetylation of carbohydrate derivatives and unprotected reducing sugars promoted by imidazole is reported. The reaction conditions have been successfully employed to acetylate carbohydrate derivatives containing acid-susceptible functional groups. In most of the cases the yields obtained were excellent. Wiley-VCH Verlag GmbH & Co. KGaA, 2005.
- Tiwari, Pallavi,Kumar, Rishi,Maulik, Prakas R.,Misra, Anup Kumar
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p. 4265 - 4270
(2007/10/03)
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- One-pot acetalation-acetylation of sugar derivatives employing perchloric acid immobilised on silica
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Perchloric acid immobilised on silica gel has been used as an efficient promoter for per-O-acetylation, and acetalation and subsequent O-acetylation of glycosides and thioglycosides in one-pot using stoichiometric reagents.
- Mukhopadhyay, Balaram,Russell, David A.,Field, Robert A.
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p. 1075 - 1080
(2007/10/03)
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- InCl3 as a powerful catalyst for the acetylation of carbohydrate alcohols under microwave irradiation
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Indium(III) chloride catalyzed microwave assisted acetylation of different carbohydrates is an efficient synthesis of per-O-acetyl derivatives and provides the products in good to excellent yields.
- Das, Saibal Kumar,Reddy, K. Anantha,Krovvidi, V. L. Narasimha Rao,Mukkanti
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p. 1387 - 1392
(2007/10/03)
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- Mild and efficient method for the cleavage of benzylidene acetals by using erbium (III) triflate
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Er(OTf)3 is proposed as new efficient Lewis acid catalyst in a mild deprotection protocol of benzylidene derivatives. In a modified procedure, where acetic anhydride is used as the reaction solvent, the simultaneous cleavage of the benzylidene acetal and the peracetylation of the substrates is obtained in quantitative yields and very short reaction times. The Royal Society of Chemistry 2005.
- Procopio, Antonio,Dalpozzo, Renato,De Nino, Antonio,Maiuolo, Loredana,Nardi, Monica,Romeo, Giovanni
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p. 4129 - 4133
(2007/10/03)
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- Iodine promoted glycosylation with glycosyl iodides: α-glycoside synthesis
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Glycosidation of fully acetylated glucopyranosyl iodide with methanol under the influence of iodine gave α-glucoside selectively. Use of less reactive acceptors led to the formation of α/β-mixtures. Glycosylations with fully benzoylated glucosyl iodide yielded β-glucosides only. In contrast, iodine-promoted glycosylation of serine and threonine with 2-azido-2-deoxy-glycosyl iodides, easily obtained in three steps, proceeded smoothly, resulting in only α-linked products in high yield in most cases. Copyright Taylor & Francis, Inc.
- Van Well, Renate M.,Kartha, K. P. Ravindranathan,Field, Robert A.
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p. 463 - 474
(2007/10/03)
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- Facile catalyzed acylation of alcohols, phenols, amines and thiols based on ZrOCl2·8H2O and acetyl chloride in solution and in solvent-free conditions
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Acylation of heteroatoms (O, N and S) with acetyl chloride based on the use of a catalytic amount of the moisture stable, inexpensive ZrOCl 2?8H2O, proceeds efficiently producing the corresponding acylated products in excellent yields.
- Ghosh, Rina,Maiti, Swarupananda,Chakraborty, Arijit
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p. 147 - 151
(2007/10/03)
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- Indium-promoted Barbier-type allylations in aqueous media: A convenient approach to 4-C-branched monosaccharides and (1→4)-C-disaccharides
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Starting from methyl 6-bromo-4,6-dideoxy-α-d-threo-4-enopyranoside, 4-C-branched sugars have been prepared through indium-promoted Barbier-type allylation of various aldehydes in aqueous media followed by hydroboration of the resulting double bond. The intermediate unsaturated monosaccharides were shown to rearrange in acidic media to give 4-C-acetyl-5-C-alkyl pyranose compounds. From β-1-formyl sugars the corresponding β-(1→4)-C- disaccharides were obtained.
- Levoirier, Eric,Canac, Yves,Norsikian, Stéphanie,Lubineau, André
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p. 2737 - 2747
(2007/10/03)
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- Simple and efficient per-O-acetylation of carbohydrates by lithium perchlorate catalyst
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Lithium perchlorate is demonstrated to be a highly efficient and convenient catalyst for the per-O-acetylation of various saccharides with excellent yields. Graphical Abstract
- Lu, Kuo-Cheng,Hsieh, Shu-Yi,Patkar, Laxmikant N.,Chen, Chien-Tien,Lin, Chun-Cheng
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p. 8967 - 8973
(2007/10/03)
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- Facile catalyzed acylation of heteroatoms using BiCl3 generated in situ from the procatalyst BiOCl and acetyl chloride
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Acylation of a variety of alcohols, phenols, aliphatic and aromatic amines, a thiol and a thiophenol proceeds efficiently using BiCl3 generated in situ from the procatalyst BiOCl and acetyl chloride in a solvent or under solventless conditions, furnishing the corresponding acylated derivatives in very good to excellent yields.
- Ghosh, Rina,Maiti, Swarupananda,Chakraborty, Arijit
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p. 6775 - 6778
(2007/10/03)
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- Conformational study of the hydroxymethyl group in α-D-mannose derivatives
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A study of the dependence of the hydroxymethyl group in α-D-mannose derivatives on the aglycon and its absolute configuration was performed by means of circular dichroism (CD) and NMR data. Depending mainly on the aglycon present, the gg or the gt rotamer was the most populated, the tg rotamer having a small population. In addition, the study showed a correlation between the rotational populations and the aglycon, the population of the gt rotamer increasing as the pKa of the bonded alcohol (aglycon) increased. Furthermore, the results revealed a strong dependence on the absolute configuration of the aglycon and point to the stereoelectronic exo-anomeric effect being responsible for these rotational dependencies besides nonbonding interactions.
- Nobrega, Chaxiraxi,Vazquez, Jesus T.
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p. 2793 - 2801
(2007/10/03)
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- Methyltrioxorhenium catalyzed domino epoxidation-nucleophilic ring opening of glycals
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The use of catalytic methylrhenium trioxide (MTO) and urea hydrogen peroxide in room temperature ionic liquid for the hydroxyglycosylation with glycals in a domino fashion is reported. Excellent conversions and good selectivities for the epoxidation reaction were observed. Application to the synthesis of glycosylphosphates, good glycosyl donors, has been studied.
- Soldaini, Gianluca,Cardona, Francesca,Goti, Andrea
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p. 5589 - 5592
(2007/10/03)
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- Towards an unprotected self-activating glycosyl donor system: Bromobutyl glycosides
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Bromobutyl mannopyranosides have been successfully used as both protected and unprotected glycosyl donors both with and without the use of an external activator.
- Davis, Benjamin G.,Wood, Steven D.,Maughan, Michael A.T.
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p. 555 - 558
(2007/10/03)
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