251 research outputs found
How to Identify Protective Carbohydrate Epitopes in the Development of a Glycoconjugate Vaccine Against Cryptococcus neoformans
No full textCryptococcus neoformans is an opportunistic pathogen that causes severe diseases and death in immunocompromised individuals. The cell wall of C. neoformans is surrounded by a polysaccharide capsule, which is the main virulence factor and thus a potential target for the development of a capsular polysaccharide based vaccine. The synthetic approaches to prepare part structures of the polysaccharide capsule are described together with the recent efforts to identify a protective epitope against this pathogen
A new route for the synthesis of Streptococcus pneumoniae 19F and 19A capsular polysaccharide fragments avoiding the beta-mannosamine glycosylation step
No full textSUMMARY The recently described (Carbohydr. Res. 2008, 43, 2545-2556) b-D-MaNAcp- (1→4)-b-D-Glcp thiophenyl glycosyl donor 3 was used in a-glycosylation reactions of OH-2 and OH-3 of the suitably protected p-MeO-benzyl a-L-rhamnopyranoside acceptors 7 and 8. The glycosylation of axial OH-2 of 7 took place in high yield (76%) and with good stereoselectivity (a/b = 3.4) leading to the protected trisaccharide a-11, corresponding to the repeating unit of Streptococcus pneumoniae 19F. The same reaction on equatorial OH-3 of acceptor 8 gave the trisaccharide a-15, constituent of the repeating unit of S. pneumoniae 19A, but in lower yield (41%) and without stereoselection (a/b = 1:1.3). Utilizing the introduced orthogonal protection of OH-1 and OH-4’’, the trisaccharide a-11 was transformed into a trisaccharide building block suitable for the synthesis of its phosphorylated oligomers
Synthesis of a Glucuronic Acid-Containing Thioglycoside Trisaccharide Building Block and Its Use in the Assembly of Cryptococcus Neoformans Capsular Polysaccharide Fragments
No full textAs part of an ongoing project aimed at identifying protective capsular polysaccharide epitopes for the development of vaccine candidates against the fungal pathogen Cryptococcus neoformans, the synthesis and glycosylation properties of a naphthalenylmethyl (NAP) orthogonally protected trisaccharide thioglycoside, a common building block for construction of serotype B and C capsular polysaccharide structures, were investigated. Et (benzyl 2,3,4-tri-O-benzyl-β-D-glucopyranosyl- uronate)-(1→2)-[2,3,4-tri-O-benzyl-β-D-xylopyranosyl-(1→4)]-6-O-benzyl-3-O-(2-naphthalenylmethyl)-1-thio-α-D-mannopyranoside was prepd. and used both as a donor and an acceptor in glycosylation reactions to obtain spacer equipped hexa- and heptasaccharide structures suitable either for continued elongation or for deprotection and printing onto a glycan array or conjugation to a carrier protein. The glycosylation reactions proceeded with high yields and α-selectivity, proving the viability of the building block approach also for construction of 4-O-xylosyl-contg. C. neoformans CPS structures
Synthesis of benzyl protected β-d-GlcA-(1 → 2)-α-d-Man thioglycoside building blocks for construction of Cryptococcus neoformans capsular polysaccharide structures
No full textIn a project targeting the synthesis of large oligosaccharide structures corresponding to the Cryptococcus neoformans GXM capsular polysaccharide, an easy access to thiodisaccharide building blocks comprising a β-linked glucuronic acid moiety and a 6-O-acetyl group was required. Several pathways to such building blocks have been investigated, addressing the problem of constructing a β-linked glucuronic acid residue protected with groups that are orthogonal to a primary acetyl group. Two efficient routes have been developed, one using benzoylated glucosyl donors to form the β-linkage followed by a change of protecting groups to benzyls and subsequent introduction of the carboxyl function and the acetyl group. The second route explored the possibility to achieve β-selectivity using glucuronyl donors without acyl protecting groups. BF3-etherate promoted glycosylations with benzyl (2,3,4-tri-O-benzyl-α-d-glucupyranosyl)uronate trichloroacetimidate in the presence of nitrile solvents and at low temps. reproducibly gave good yields of disaccharides with high β-selectivity. Furthermore, the use of recently reported glucuronyl thioglycoside donors protected with a cyclic 2,4-silylene acetal was found to represent another efficient and completely β-selective way to desired disaccharide building blocks
Synthesis of part structures of Cryptococcus neoformans serotype C capsular polysaccharide
No full textCryptococcus neoformans is a fungal pathogen that can cause life-threatening infections in immunocompromised patients. The development of a vaccine based on the capsular polysaccharide of C. neoformans is still an open challenge due to the heterogeneity of the capsular polysaccharide and the difficulty of identifying protective epitopes. Therefore, construction of structurally defined part structures of the C. neoformans GXM capsule is in great demand. Herein is presented the synthesis of a 3-O-naphthalenylmethyl protected trisaccharide thioglycoside building block which is present in C. neoformans serotype C polysaccharide. Its property as a donor in a glycosylation reaction with a model acceptor has been evaluated together with its behaviour as an acceptor following removal of the temporary protecting group. The heavily branched hexasaccharide was obtained in good yields and excellent α-selectivity. The frame shifted octasaccharide structural triad motif for serotype C was also prepared following the same building block strategy. For the first time this structural motif, which is the most substituted amongst the four C. neoformans serotypes, was prepared. Three synthesized C. neoformans serotype C fragments of varying size, from penta-up to octasaccharide, were deprotected and will be included in unique glycoarrays to further investigate the possibility to develop a synthetic vaccine against this pathogen
Large scale synthesis and regioselective protection schemes of ethyl 2-azido-2-deoxy-1-thio-alpha-D-cellobioside for preparation of heparin thiodisaccharide building blocks
No full textCrystalline acetylated ethyl 2-azido-2-deoxy-1-thio-a-D-cellobioside has been prepared on a multigram scale from cellobiose in an overall yield of 23% with no chromatography required and converted after deacetylation into the 40,60-O-benzylidene and 40,60-O-benzylidene-6-O-TBDMS protected derivatives. Applying a number of regioselective benzylation methods on these gave access to a variety of regioselectively protected derivatives, both mono-ols (20- and 3-OH), diols (20,6-, 20,3-, and 3,6-di-OH), and triols (20,3,6- and 20,30,3-tri-OH). A number of these derivatives were further processed by benzoylation followed by removal or opening of the benzylidene acetal and selective oxidation of the exposed primary alcohol to give heparin building block intermediates comprising a range of possible sulfation patterns
A synthetic strategy to xylose-containing thioglycoside tri- and tetrasaccharide building blocks corresponding to Cryptococcus neoformans capsular polysaccharide structures
No full textAs part of an ongoing project aimed at developing vaccine candidates against Cryptococcus neoformans the prepn. of tri- and tetrasaccharide thioglycoside building blocks, to be used in construction of structurally defined part structures of C. neoformans GXM capsular polysaccharide, was investigated. Using a naphthalenylmethyl (NAP) ether as a temporary protecting group and trichloroacetimidate donors in optimized glycosylations the target building blocks, Et 6-O-acetyl-2,4-di-O-benzyl-3-O-(2-naphthalenylmethyl)-α-D-mannopyranosyl-(1→3)-[2,3,4-tri-O-benzyl-β-D-xylopyranosyl-(1→2)]-4,6-di-O-benzyl-1-thio-α-D-mannopyranoside (16) and Et 2,3,4-tri-O-benzyl-β-D-xylopyranosyl-(1→2)-4,6-di-O-benzyl-3-O-(2-naphthalenylmethyl)-α-D-mannopyranosyl-(1→3)-[2,3,4-tri-O-benzyl-β-D-xylopyra-nosyl-(1→2)]-6-O-acetyl-4-O-benzyl-1-thio-α-D-mannopyranoside (21), were efficiently prepd. These synthesized thiosaccharide building blocks were then used as donors in high-yielding (∼90%) DMTST promoted glycosylations to a spacer-contg. acceptor to, after deprotection, afford GXM polysaccharide part structures ready for protein conjugation to give vaccine candidates. Also, the NAP groups in the building blocks were removed to obtain tri- and tetrasaccharide acceptors suitable for further elongation towards larger thiosaccharide building blocks
Alternate synthesis to d-glycero-\u3b2-d-manno-heptose 1,7-biphosphate
No full textd-glycero-\u3b2-d-manno-heptose 1,7-biphosphate (HBP) is an enzymatic intermediate in the biosynthesis of the heptose component of lipopolysaccharide (LPS), and was recently revealed to be a pathogen-associated molecular pattern (PAMP) that allows detection of Gram-negative bacteria by the mammalian immune system. Cellular detection of HBP depends upon its stimulation of a cascade that leads to the phosphorylation and assembly of the TRAF-interacting with forkhead-associated domain protein A (TIFA), which activates the transcription factor NF-\u3baB. In this note, an alternate chemical synthesis of HBP is described and its biological activity is established, providing pure material for further assessing and exploiting the biological activity of this compound.Peer reviewed: YesNRC publication: Ye
Isothermal titration calorimetric study defines the substrate binding residues of calreticulin
No full textEarlier we established using modeling studies the residues in calreticulin (CRT) important for sugar-binding (M. Kapoor, H. Srinivas, K. Eaazhisai, E. Gemma, L. Ellgaard, S. Oscarson, A. Helenius, A. Surolia, Interactions of substrate with calreticulin, an endoplasmic reticulum chaperone, J. Biol. Chem. 278 (8) (2003) 6194-6200). Here, we discuss the relative roles of Trp-319, Asp-317, and Asp-160 for sugar-binding by using site-directed mutagenesis and isothermal titration calorimetry (ITC). Residues corresponding to Asp-160 and Asp-317 in CNX play important role towards sugar-binding. From the present study we demonstrate that the residue Asp-160 is not involved in sugar-binding, while Asp-317 plays a crucial role. Further, it is also validated that cation-π interactions of the sugar with Trp-319 dictate sugar-binding in CRT. This study not only defines further the binding site of CRT but also highlights its subtle differences with that of calnexin
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