Facile synthesis of a pentasaccharide repeating unit corresponding to the common O-antigen of Salmonella enterica O57 and Escherichia coli O51

A concise chemical synthetic strategy has been developed for the synthesis of a pentasaccharide present in the O-antigen of Salmonella enterica O57 and Escherichia coli O51 strains. A sequential glycosylation strategy has been adopted for the synthesis of the target pentasaccharide. All intermediate steps are high yielding and the glycosylation steps are stereoselective. A number of recently developed methodologies have been used in the synthesis.     

Concise synthesis of a pentasaccharide repeating unit corresponding to the O-antigen of Escherichia coli O102

An efficient synthetic strategy has been developed for the synthesis of a pentasaccharide repeating unit of the O-antigen of Escherichia coli O102 strain. The target pentasaccharide 1 has been synthesized using a [2+3] block glycosylation strategy. All glycosylation steps are highly stereoselective and high yielding. Concept of armed-disarmed and orthogonal glycosylation strategies has been applied during the synthesis. The target compound has been synthesized using the minimum number of steps.     

Straightforward sequential and one-pot synthesis of a pentasaccharide repeating unit corresponding to the cell wall O-antigen of Shigella boydii type 18

Synthesis of a pentasaccharide repeating unit corresponding to the cell of wall O-antigen Shigella boydii type 18 has been achieved by sequential as well as iterative glycosylations in one-pot. Use of p-methoxybenzyl group (PMB) as an in situ removable protecting group allowed obtaining the desired pentasaccharide derivative in a generalized glycosylation condition and in one-pot condition. Synthesis of a beta-L-rhamnosidic linkage present in the molecule has been successfully achieved using l-rhamnosyl thioglycoside donor having a picoloyl group at remote C-3 position influencing beta selectivity in the glycosylation. A combination of N-iodosuccinimide (NIS) and perchloric acid supported over silica (HClO₄–SiO₂) has been used as thiophilic glycosylation promoter in all glycosylation reactions. TEMPO mediated selective oxidation of the primary hydroxyl group has been carried out at the late stage of the synthetic strategy.     

Synthetic routes toward pentasaccharide repeating unit corresponding to the O-antigen of Escherichia coli O181

An efficient synthetic strategy has been developed for the synthesis of the pentasaccharide repeating unit corresponding to the O-antigen of Escherichia coli O181. A one-pot, two step iterative glycosylation and [2?+?3] block glycosylation strategy have been adopted for the construction of the pentasaccharide derivative 2, which was then transformed into target compound 1 after a series of functional group transformations. Here H₂SO₄-silica has been used successfully as a promoter for all glycosylation reaction. The stereoselective outcomes of all glycosylation reactions were very good. The 2-acetamido-2,6-dideoxy-l-glucose (l-QuipNAc) building block was obtained from known carbohydrate l-rhamnose precursors.     

Expedient synthesis of a tetrasaccharide and a pentasaccharide corresponding to the cell wall O-antigen of Escherichia coli O77 and Escherichia coli O17

A concise chemical synthetic strategy has been developed for the synthesis of a tetrasaccharide and a pentasaccharide corresponding to the O-antigen of Escherichia coli O77 and E. coli O17 strains, respectively using [2+2] and [3+2] block glycosylation approaches from suitably functionalized common monosaccharide intermediates. All of the intermediate steps are high yielding while the glycosylation steps are highly stereoselective. A number of recently developed methodologies have been used in the synthesis.     

Synthesis of a pentasaccharide repeating unit of the O-antigen of enteroadherent Escherichia coli O154 strain

A straightforward linear synthetic strategy has been developed for the synthesis of the pentasaccharide repeating unit of the cell wall O-antigenic polysaccharide of enteroadherent Escherichia coli O154 strain. Newly developed glycosylation conditions using glycosyl trichloroacetimidate derivatives as glycosyl donors and nitrosyl tetrafluoroborate as the glycosylation activator have been used in all of the glycosylation reactions throughout the synthetic scheme. The stereochemical outcomes of the glycosylations were excellent and the yields were very good.     

Synthesis of the hexasaccharide repeating unit corresponding to the cell wall lipopolysaccharide of Azospirillum irakense KBC1

A convenient chemical synthesis of the hexasaccharide repeating unit of the cell wall lipopolysaccharide of Azospirillum irakense KBC1 has been successfully achieved. A stereo- and regioselective [4 + 2] block glycosylation strategy has been used to obtain the target hexasaccharide as its octyl glycoside. All synthetic intermediates have been prepared in high yields from commercially available reducing sugars following a series of protection–deprotection reactions. An oxidation–reduction methodology has been applied to convert β-d-glucosidic unit to a β-d-mannosidic moiety.     

First synthesis of a pentasaccharide repeating unit of the O-antigenic polysaccharide from enterohaemorrhagic Escherichia coli O48:H21

A concise synthesis of a pentasaccharide as its 4-methoxyphenyl glycoside, found in the O-antigenic polysaccharide of enterohaemorrhagic Escherichia coli O48:H21 has been achieved for the first time in excellent yield. Most of the intermediate steps are high yielding and the stereooutcome of each glycosylation step was excellent. Stereoselective glycosylation and removal of the 4-methoxybenzyl group were achieved in one-pot by tuning the reaction conditions. A late-stage TEMPO-mediated oxidation strategy has been adopted for the oxidation of a primary hydroxyl group to carboxylic acid.     

First synthesis of C. difficile PS-II cell wall polysaccharide repeating unit

Clostridium difficile is the most commonly diagnosed cause of nosocomial diarrhea with increasing incidence and mortality among elderly and hospitalized patients. We report the first synthesis of the surface polysaccharide PS-II repeating unit and its nonphosphorylated analogue, with a linker for conjugation, via a (4 + 2) convergent approach from a common AB(D)C tetrasaccharide intermediate.     

Blockwise synthesis of a pentasaccharide structurally related to the mannan fragment from the Candida albicans cell wall corresponding to the antigenic factor 6

Russian Chemical Bulletin - A spacer-armed pentasaccharide structurally related to a fragment of the mannan from the cell wall of the fungus Candida albicans and corresponding to the antigenic...     

Synthesis of tri- and pentasaccharide fragments corresponding to the O-antigen of Shigella boydii type 6

A convenient synthetic strategy for the synthesis of the acidic pentasaccharide repeating unit and its trisaccharide fragment corresponding to the O-antigen of Shigella boydii type 6 has been successfully developed. A stereoselective sequential glycosylation method has been exploited to obtain the target tri- and pentasaccharide derivatives. Most of the synthetic intermediates were solid and prepared in high yields from commercially available reducing sugars following a series of protection–deprotection reactions. A late-stage TEMPO mediated selective oxidation reaction finally resulted in the pentasaccharide containing a glucuronic acid unit. A 2-(4-methoxyphenoxy) ethyl group has been chosen as the anomeric protecting group to provide trisaccharide and pentasaccharide derivatives linked to an ethylene glycol linker.     

Expedient synthesis of two structurally close tetrasaccharides corresponding to the O-antigens of Escherichia coli O127 and Salmonella enterica O13

Two structurally close tetrasaccharides corresponding to the O-antigens of Escherichia coli O127 and Salmonella enterica O13 have been synthesized using a ‘unichemo’ approach and minimum number of reaction steps. The yields of all glycosylation steps were excellent with a high stereochemical outcome. A common synthetic strategy has been adopted for the simultaneous synthesis of two tetrasaccharides.     

First synthesis of the beta-D-rhamnosylated trisaccharide repeating unit of the O-antigen from Xanthomonas campestris pv. campestris 8004

The trisaccharide repeating unit of the O-antigen of the lipopolysaccharide from Xanthomonas campestris pv. campestris 8004, a pathogen of cruciferous crops, presents some structural features that renders it a challenging synthetic target: the presence of a beta-D-rhamnosidic linkage, the steric crowd on a 1,2-cis-diglycosylated D-rhamnose, and finally the noncommercial availability of its monosaccharide constituents. The synthesis of this trisaccharide as methyl glycoside has been accomplished by exploiting a strategy whose key steps were the sequential beta-D-rhamnosylation with a 2-O-benzylsulfonyl-N-phenyltrifluoroacetimidate donor, debenzylsulfonylation, and coupling with a D-Fucp3NAc thioglycoside donor.     

Convergent synthesis of the tetrasaccharide repeating unit related to the O-antigenic polysaccharide of Escherichia coli 78

A convergent synthesis of the tetrasaccharide repeating unit of the O-antigenic cell wall polysaccharide of Escherichia coli 78, as the corresponding methyl glycoside (I), is being reported. It involved stereoselective glycosidation of a β-linked mannodisaccharide acceptor with a β-linked glucosamine based disaccharide thioglycoside donor, which were prepared from the corresponding functionalised monosaccharide based glycosyl donors and acceptors. The resulting tetrasaccharide derivative was finally converted to (I) by selective deprotection and also by global protection and deprotection techniques.     

Synthesis of the pentasaccharide repeating unit of the O-specific polysaccharide from salmonella strasbourg

The pentasaccharide α - Tyv - (1→3) - β - d - Man - (1→4) - α - l - Rha - (1→3) - d - Gal - (4←1) -α - d - Glc 1, the repeating unit of the O-specific polysaccharide chain of the lipopolysaccharide from S. Strasbourg, was obtained by glycosylation of benzyl - 2,6 - di - O - benzyl - 4 - O - (2,3,4 - tri - O - benzyl - 6 - O - benzoyl - α - d - glucopyranosyl) - β - d - galactopyranoside with 1,2 - methylorthoacetyl - 3 - O - acetyl - 4- O - [3 - O - (2,4 - di - O - acetyl - 3, 6 - dideoxy,- α - d - arabino - hexopyranosyl) - 2,4,6 - tri - O - acetyl - β - d - mannopyranosyl] - β - l - rhamnopyranose 3 followed by removal of protecting groups. The structure of the synthetic pentasaccharide was proved by methylation analysis and ¹³C NMR.     

Synthesis of a derivative of a pentasaccharide repeating unit of the O-antigenic polysaccharide of the bacterium Klebsiella pneumoniae O3 as a benzoylated 2-methoxycarbonylethyl thioglycoside

Block synthesis of a fully benzoylated derivative of the pentasaccharide α-d-Manp-(1→3)-α-d-Manp-(1→2)-α-d-Manp-(1→2)-α-d-Manp-(1→2)-α-d-Manp-SCH₂CH₂CO₂Me, the glycoside of the repeating unit of the O-antigenic polysaccharide of the bacterium Klebsiella pneumoniae O3, was performed.     

Convergent synthesis of a common pentasaccharide-repeating unit corresponding to the O-specific polysaccharide of Escherichia coli O4:K3, O4:K6, and O4:K12

A convergent chemical synthesis of a pentasaccharide found in the O-specific polysaccharide of Escherichia coli O4:K3, O4:K6, and O4:K12 has been achieved in excellent yield. A [3+2] block synthetic strategy has been adopted to couple a disaccharide donor 11 with a trisaccharide acceptor 10 for the construction of the pentasaccharide derivative 12 which on deprotection furnished target pentasaccharide 1 as its 4-methoxyphenyl glycoside. Disaccharide thioglycoside donor 11 and trisaccharide acceptor 10 were prepared from suitably protected monosaccharide intermediates. Yields were excellent in all steps.     

Characterization of the core oligosaccharide and the O-antigen biological repeating unit from Halomonas stevensii lipopolysaccharide: the first case of O-antigen linked to the inner core

A novel core structure among bacterial lipopolysaccharides (LPS) that belong to the genus Halomonas has been characterized. H. stevensii is a moderately halophilic microorganism, as are the majority of the Halomonadaceae. It brought to light the pathogenic potential of this genus. On account of their role in immune system elicitation, elucidation of LPS structure is the mandatory starting point for a deeper understanding of the interaction mechanisms between host and pathogen. In this paper we report the structure of the complete saccharidic portion of the LPS from H. stevensii. In contrast to the finding that the O-antigen is usually covalently linked to the outer core oligosaccharide, we could demonstrate that the O-polysaccharide of H. stevensii is linked to the inner core of an LPS. By means of high-performance anion-exchange chromatography with pulsed amperometric detection we were able to isolate the core decasaccharide as well as a tridecasaccharide constituted by the core region plus one O-repeating unit after alkaline degradation of the LPS. The structure was elucidated by one- and two-dimensional NMR spectroscopy, ESI Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry, and chemical analysis.