The Experts below are selected from a list of 165 Experts worldwide ranked by ideXlab platform
Laurence A Mulard - One of the best experts on this subject based on the ideXlab platform.
-
Total synthesis of a tetra- and two pentasaccharide fragments of the O-specific polysaccharide of Shigella flexneri serotype 2a
Tetrahedron, 2004Co-Authors: Laurence A Mulard, Catherine GuerreiroAbstract:The synthesis of the Methyl Glycoside of the branched pentasaccharide biological repeating unit of the O-antigen of Shigella flexneri serotype 2a is described together with that of the Methyl Glycoside of the corresponding tetrasaccharide and frame-shifted linear pentasaccharide. All the strategies disclosed herein involve a key disaccharide corresponding to the branching point and otherwise appropriate monosaccharide building blocks activated as their trichloroacetimidate. Our data suggest partial lack of conformational flexibility at the branched residue.
-
synthesis of the Methyl Glycoside of a branched octasaccharide fragment specific for the shigella flexneri serotype 2a o antigen
Tetrahedron Letters, 2002Co-Authors: Frederic Belot, Corina Costachel, Karen Wright, Armelle Phalipon, Laurence A MulardAbstract:An efficient synthesis of the Methyl Glycoside of a branched octasaccharide representative of Shigella flexneri serotype 2a O-specific polysaccharide is described. The synthesis is based on the use of the trichloroacetimidate methodology, and involves the condensation of a pentasaccharide acceptor and a trisaccharide donor as the key step.
Thierry Doco - One of the best experts on this subject based on the ideXlab platform.
-
Determination of Must and Wine Polysaccharides by Gas Chromatography–Mass Spectrometry (GC–MS) and Size-Exclusion Chromatography (SEC)
Polysaccharides, 2021Co-Authors: Zenaida Guadalupe, Belén Ayestarán, Pascale Williams, Thierry DocoAbstract:Polysaccharides are one of the major classes of macromolecules found in wines. They play a critical role in stabilizing other molecules in solution and thus are able to modify both the wine processing and organoleptic properties. Detailed analyses of these polysaccharides are essential to know their physicochemical properties and biological functions.We present analytical techniques not only to define the fine chemical structures of individual wine polysaccharides but also to estimate the overall polysaccharide composition of must and wines. The procedure covers the preparation of the sample, together with gas chromatography–mass spectrometry-based methods, for both the analysis of monosaccharides as their volatile triMethylsilyl Methyl Glycoside derivatives and for Methylation analysis to determine linkage positions between monosaccharide residues as their volatile partially Methylated alditol acetate derivatives. We also provide a protocol for estimating the global content of wine polysaccharides by using size-exclusion chromatography with refractive index detector (SEC-RID). This is a rapid and simple method that can be used routinely in a reasonably equipped laboratory. Analysis complexity and time will vary depending on the method used, and the duration ranges from 2 days for a global polysaccharide estimation to 2 weeks for a carboxyl reduction/Methylation linkage analysis.
-
Determination of Must and Wine Polysaccharides by Gas Chromatography-Mass Spectrometry (GC-MS) and Size-Exclusion Chromatography (SEC)
2014Co-Authors: Zenaida Guadalupe, Belén Ayestarán, Pascale Williams, Thierry DocoAbstract:Polysaccharides are one of the major classes of macromolecules found in wines. They play a critical role in stabilizing other molecules in solution and thus are able to modify both the wine processing and organoleptic properties. Detailed analyses of these polysaccharides are essential to know their physicochemical properties and biological functions. We present analytical techniques not only to define the fine chemical structures of individual wine polysaccharides but also to estimate the overall polysaccharide composition of must and wines. The procedure covers the preparation of the sample, together with gas chromatography-mass spectrometry-based methods, for both the analysis of monosaccharides as their volatile triMethylsilyl Methyl Glycoside derivatives and Methylation analysis to determine linkage positions between monosaccharide residues as their volatile partially Methylated alditol acetate derivatives. We also provide a protocol for estimating the global content of wine polysaccharides by using size-exclusion chromatography with refractive index detector (SEC-RID). This is a rapid and simple method that can be used routinely in a reasonably equipped laboratory. Analysis complexity and time will vary depending on the method used, and the duration ranges from 2 days for a global polysaccharide estimation to 2 weeks for a carboxyl reduction/Methylation linkage analysis.
-
determination of the neutral and acidic glycosyl residue compositions of plant polysaccharides by gc ei ms analysis of the triMethylsilyl Methyl Glycoside derivatives
Carbohydrate Polymers, 2001Co-Authors: Thierry Doco, Malcolm A Oneill, Patrice PellerinAbstract:A method, using GC-EI-MS analysis of the triMethylsilyl Methyl Glycoside derivatives, has been developed to identify the neutral and acidic glycosyl-residue compositions of plant polysaccharides. Monosaccharides (15) including four pentoses (arabinose, xylose, 2-O-Methylxylose, and apiose), three hexoses (galactose, glucose, and mannose), three 6-deoxy hexoses (rhamnose, fucose, and 2-O-Methylfucose), two hexuronic acids (galacturonic and glucuronic acids), two 2-keto-3-deoxy sugars (Kdo and Dha), and aceric acid were quantified. The monosaccharide derivatives were identified by their retention times and by their characteristic GC-MS fragmentation patterns. These monosaccharides are components of plant cell wall polysaccharides and red wine polysaccharides. Thus, GC-MS analysis of triMethylsilyl Methyl Glycoside derivatives is suitable for determining the neutral and acidic glycosyl-residue compositions of plant cell wall polysaccharides and of polysaccharides present in plant-derived foods and beverages.
Samuel J. Danishefsky - One of the best experts on this subject based on the ideXlab platform.
-
a total synthesis of the Methyl Glycoside of ganglioside gm 1
Journal of Organic Chemistry, 2000Co-Authors: Samit K Bhattacharya, Samuel J. DanishefskyAbstract:The total synthesis of the Methyl Glycoside of GM1 (1b) has been accomplished. The key step in the synthesis involves the sulfonamidoglycosidation reaction, which is used to create a β-linkage leading to a GalNAc residue joined to the C4 hydroxyl group of a galactose unit of a C3 sialylated lactosyl moiety. The “proximal hydroxyl” directing effect, which has been postulated before, manifests in this context as well leading to the preponderant formation of the β-Glycoside. Together with asialo GM1 and other substructures, the GM1 Methyl Glycoside has been submitted for biological assays as potential ligands for bacterial and viral infection sites.
-
specific inhibition of formation of transcription complexes by a calicheamicin oligosaccharide a paradigm for the development of transcriptional antagonists
Proceedings of the National Academy of Sciences of the United States of America, 1994Co-Authors: Steffan N. Ho, Serge H Boyer, Stuart L. Schreiber, Samuel J. Danishefsky, Gerald R CrabtreeAbstract:Sequence-specific DNA ligands that antagonize DNA-protein interactions represent a potentially powerful means of modulating gene expression. Calicheamicin gamma 1I, a member of the DNA-cleaving enediyne class of anticancer antibiotics, binds to specific DNA sequences through an aryltetrasaccharide domain. To take advantage of this unique sequence-specific recognition capability, the Methyl Glycoside of the aryltetrasaccharide of calicheamicin gamma 1I (CLM-MG) was used to investigate the ability of glycoconjugate DNA ligands to inhibit DNA-protein interactions. CLM-MG inhibits the formation of DNA-protein complexes at micromolar concentrations in a sequence-specific manner and rapidly dissociates preformed complexes. CLM-MG also inhibits transcription in vivo with similar sequence specificity. These results suggest a strategy for the development of a class of novel biological probes and therapeutic agents.
Fanzuo Kong - One of the best experts on this subject based on the ideXlab platform.
-
Synthesis of a heptasaccharide fragment of the O-deacetylated GXM of C. neoformans serotype C.
Carbohydrate research, 2005Co-Authors: Wei Zhao, Fanzuo KongAbstract:Beta-D-Xylp-(1-->2)-alpha-D-Manp-(1-->3)-[beta-D-Xylp-(1-->2)][beta-D-Xylp-(1-->4)]-alpha-D-Manp-(1-->3)-[beta-D-Xylp-(1-->4)]-alpha-D-Manp, the fragment of the exopolysaccharide from Cryptococcus neoformans serovar C, was synthesized as its Methyl Glycoside. Thus, chloroacetylation of allyl 3-O-acetyl-4,6-O-benzylidene-alpha-D-mannopyranoside (1) followed by debenzylidenation and selective 6-O-benzoylation afforded allyl 2-O-chloroacetyl-3-O-acetyl-6-O-benzoyl-alpha-D-mannopyranoside (4). Glycosylation of 4 with 2,3,4-tri-O-benzoyl-D-xylopyranosyl trichloroacetimidate (5) furnished the beta-(1-->4)-linked disaccharide 6. Dechloroacetylation gave the disaccharide acceptor 7 and subsequent coupling with 5 produced the trisaccharide 8. Deacetylation of 8 gave the trisaccharide acceptor 9 and subsequent coupling with a disaccharide 10 produced the pentasaccharide 11. Reiteration of deallylation and trichloroacetimidate formation from 11 yielded the pentasaccharide donor 12. Coupling of a disaccharide acceptor 13 with 12 afforded the heptasaccharide 14. Subsequent deprotection gave the heptaoside 16, while selective 2-O-deacetylation of 14 gave the heptasaccharide acceptor 15. Condensation of 15 with glucopyranosyluronate imidate 17 did not yield the expected octaoside, instead, an orthoester product 18 was obtained. Rearrangement of 18 did not give the target octaoside; but produced 15. Meanwhile, there was no reaction between 15 and the glycosyl bromide donor 19.
-
facile synthesis of the heptasaccharide repeating unit of o deacetylated gxm of c neoformans serotype b
Bioorganic & Medicinal Chemistry, 2005Co-Authors: Wei Zhao, Fanzuo KongAbstract:Abstract A heptasaccharide, β- d -Xyl p -(1→2)-α- d -Man p -(1→3)-[β- d -Xyl p -(1→2)]-α- d -Man p -(1→3)-[β- d -Glc p A-(1→2)][β- d -Xyl p -(1→4)]-α- d -Man p , the repeating unit of the exopolysaccharide from Cryptococcus neoformans serovar B, was synthesized as its Methyl Glycoside. Thus 2,3,4-tri- O -benzoyl-β- d -xylopyranosyl-(1→2)-3,4,6-tri- O -benzoyl-α- d -mannopyranosyl trichloroacetimidate ( 7 ) and allyl 2,3,4-tri- O -benzoyl-β- d -xylopyranosyl-(1→2)-4,6-di- O -benzoyl-α- d -mannopyranoside ( 8 ), readily obtained from the corresponding monosaccharide derivatives via simple transformation, were coupled to give a (1→3)-linked tetrasaccharide 9 . Deallylation of 9 followed by trichloroacetimidate formation produced the tetrasaccharide donor 11 . Condensation of Methyl 2,3,4-tri- O -benzoyl-β- d -xylopyranosyl-(1→4)-2- O -acetyl-6- O -benzoyl-α- d -mannopyranoside ( 18 ) with 11 followed by selective deacetylation yielded hexasaccharide acceptor 20 . Coupling of 20 with Methyl 2,3,4-tri- O -acetyl-α- d -glucopyranosyluronate bromide ( 21 ) and subsequent deprotection furnished the target heptaoside. A hexasaccharide fragment, α- d -Man p -(1→3)-[β- d -Xyl p -(1→2)]-α- d -Man p -(1→3)-[β- d -Glc p A-(1→2)][β- d -Xyl p -(1→4)]-α- d -Man p , was also similarly synthesized as its Methyl Glycoside.
-
synthesis of a heptasaccharide fragment of the o deacetylated gxm of c neoformans serotype c
Carbohydrate Research, 2004Co-Authors: Wei Zhao, Fanzuo KongAbstract:Abstract β- d -Xyl p -(1 → 4)-α- d -Man p -(1 → 3)-[β- d -Xyl p -(1 → 2)]-α- d -Man p -(1 → 3)-[β- d -Xyl p -(1 → 2)]-α- d -Man p , the fragment of the exopolysaccharide from Cryptococcus neoformans serovar B, was synthesized as its Methyl Glycoside. Thus, acetylation of allyl 3- O -benzoyl-4,6- O -benzylidene-α- d -mannopyranoside ( 1 ) followed by debenzylidenation and selective 6-O-benzoylation afforded allyl 2- O -acetyl-3,6-di- O -benzoyl-α- d -mannopyranoside ( 4 ). Glycosylation of 4 with 2,3,4-tri- O -benzoyl- d -xylopyranosyl trichloroacetimidate ( 5 ) furnished the β-(1 → 4)-linked disaccharide 6 . Deallylation followed by trichloroacetimidate formation gave the disaccharide donor 8 , and subsequent coupling with allyl 2,3,4-tri- O -benzoyl-β- d -xylopyranosyl-(1 → 2)-4,6-di- O -benzoyl-α- d -mannopyranoside ( 9 ), produced the tetrasaccharide 10 . Reiteration of deallylation and trichloroacetimidate formation from 10 yielded the tetrasaccharide donor 12 . The downstream disaccharide acceptor 18 was obtained by condensation of 5 with Methyl 3- O -acetyl-4,6- O -benzylidene-α- d -mannopyranoside, followed by debenzylidenation, benzoylation, and selective 3-O-deacetylation. Coupling of 18 with 12 afforded the hexasaccharide 19 , and subsequent deprotection gave the hexasaccharide Glycoside 20 . Selective 2″-O-deacetylation of 19 gave the hexasaccharide acceptor 21 . Condensation of 21 with glucopyranosyluronate imidate 22 did not produce the expected heptasaccharide Glycoside; instead, a transacetylation product 19 was obtained. Meanwhile, there was no reaction between 21 and the bromide donor 23 .
-
efficient synthesis of a heptasaccharide the repeating unit of the o chain lipopolysaccharide produced by xanthomonas campestris strain 642
Carbohydrate Research, 2003Co-Authors: Jianjun Zhang, Jun Ning, Fanzuo KongAbstract:α-l-Rhap-(1→3)-α-l-Rhap-(1→2)-α-l-Rhap-(1→3)-[β-d-Xylp-(1→2)-][β-d-Xylp-(1→4)-]α-l-Rhap-(1→3)-α-l-Rhap, the repeating unit of the O-chain lipopolysaccharide produced by Xanthomonas campestris strain 642 was synthesized as its Methyl Glycoside via 3-O-selective glycosylation of Methyl α-l-rhamnopyranosyl-(1→3)-2,4-di-O-benzoyl-α-l-rhamnopyranoside (9) with 2,3,4-tri-O-benzoyl-α-l-rhamnopyranosyl-(1→3)-2,4-di-O-benzoyl-α-l-rhamnopyranosyl-(1→2)-3,4-di-O-benzoyl-α-l-rhamnopyranosyl trichloroacetimidate (8), followed by dixylosylation with 2,3,4-tri-O-benzoyl-α,β-d-xylopyranosyl trichloroacetimidate (12) and subsequent deacylation.
Frederic Belot - One of the best experts on this subject based on the ideXlab platform.
-
synthesis of the Methyl Glycoside of a branched octasaccharide fragment specific for the shigella flexneri serotype 2a o antigen
Tetrahedron Letters, 2002Co-Authors: Frederic Belot, Corina Costachel, Karen Wright, Armelle Phalipon, Laurence A MulardAbstract:An efficient synthesis of the Methyl Glycoside of a branched octasaccharide representative of Shigella flexneri serotype 2a O-specific polysaccharide is described. The synthesis is based on the use of the trichloroacetimidate methodology, and involves the condensation of a pentasaccharide acceptor and a trisaccharide donor as the key step.
-
Unexpected stereochemical outcome of activated 4,6-O-benzylidene derivatives of the 2-deoxy-2-trichloroacetamido-d-galacto series in glycosylation reactions during the synthesis of a chondroitin 6-sulfate trisaccharide Methyl Glycoside
Carbohydrate Research, 2000Co-Authors: Frederic Belot, Jean-claude JacquinetAbstract:Abstract The synthesis of Methyl (β- d -glucopyranosyluronic acid)-(1→3)-(2-acetamido-2-deoxy-6- O -sulfonato-β- d -galactopyranosyl)-(1→4)-(β- d -glucopyranosid)uronate trisodium salt, a chondroitin 6-sulfate trisaccharide derivative, is described. Loss of stereocontrol in glycosylation reactions involving activated 4,6- O -benzylidene derivatives of the 2-deoxy-2-trichloroacetamido- d - galacto series and d -glucuronic acid-derived acceptors was highlighted. This drawback was overcome through the use of phenyl 3,4,6-tri- O -acetyl-2-deoxy-1-thio-2-trichloroacetamido-β- d -galactopyranoside, which afforded the desired β-linked disaccharide derivative in high yield with an excellent stereoselectivity. This later was submitted to acid-catalyzed methanolysis, followed by benzylidenation, and condensed with Methyl 2,3,4-tri- O -benzoyl-1- O -trichloroacetimidoyl-α- d -glucopyranuronate to afford the expected trisaccharide derivative. Subsequent transformation of the N -trichloroacetyl group into N -acetyl, mild acid hydrolysis, selective O-sulfonation at C-6 of the amino sugar moiety, and saponification afforded the target molecule as its sodium salt in high yield.