Chemical synthesis of the tetrasaccharide repeating unit of the O-antigenic polysaccharide from Plesiomonas shigelloides strain AM36565

Chemical synthesis of the pentasaccharide repeating unit of the O-antigen from Escherichia coli strain SDLZB008 in the form of its 2-aminoethyl glycoside

Chemical synthesis of the pentasaccharide repeating unit of the O-antigen from E. coli strain SDLZB008 is accomplished through a linear strategy using rationally protected monosaccharide derivatives ensuring desired stereochemical outcome up on glycosylations. 2-Aminoethyl glycoside is incorporated at the reducing end of the target pentasaccharide. The terminal free amine may be used for further conjugation with suitable aglycon without hampering the reducing end stereochemistry. The rare D-Fucp3NAc moiety is incorporated through the corresponding 3-azido derivative derived from a known 3-azido quinovose derivative.

Chemical synthesis of the pentasaccharide repeating unit of the O-specific polysaccharide from Ruminococcus gnavus

Microorganisms present in the guts are the causative agents for various diseases in humans. More and more studies are correlating such diseases and the responsible microorganism. The Gram-positive bacterium Ruminococcus gnavus (R. gnavus) has been identified to be responsible for symptoms of Crohn's disease. R. gnavas produces a glucorhamnan polysaccharide and it is postulated that this polysaccharide induces inflammatory response through toll-like receptor 4 (TLR4). The current manuscript describes the chemical synthesis of the pentasaccharide repeating unit of the O-polysachharide from R. gnavus. The major challenge associated with this particular synthesis is the presence of two consecutive 1,2-cis glucose units. The target oligosaccharide is achieved through a linear strategy from commercially available sugars through rational protecting group manipulation. 1,2-cis glycosylation of glucose through remote participation of acyl group at the 6-O position is used successfully with excellent yield. In both cases, sole 1,2-cis products are obtained at -20 °C through the activation of thioglycosides.

Synthesis of the pentasaccharide repeating unit of the O-antigen from Enterobacter cloacae C4115 containing the rare α-d-FucNAc

Total synthesis of the pentasaccharide repeating unit associated with the O-antigen of Enterobacter cloacae C4115 is reported. The synthesis of the said oligosaccharide was accomplished through rational protecting group manipulations on commercially available monosaccharides followed by stereoselective glycosylations either by activation of thioglycosides or glycosyl trichloroacetimidates and was found to be productive. Towards the synthesis of the rare sugar unit, α-d-FucNAc in this case, it was established that the methoxymethyl (MOM) group is advantageous over the earlier reported tetrahydro pyran (THP) protection. The effect of MOM-protection was successfully tested for the synthesis of a rare sugar synthon which can serve as a precursor to the rare d-fucosamine residue.

Synthesis of the tetrasaccharide related to the repeating unit of the O-antigen from Azospirillum brasilense Jm125A2 in the form of its 2-aminoethyl glycoside

Total chemical synthesis of the linear tetrasaccharide repeating unit β-D-Glc-(1 → 2)-α-L-Rha-(1 → 3)-α-L-Rha-(1 → 2)-α-L-Rha-CH₂CH₂NH₂ of the O-antigen from Azospirillum brasilense Jm125A2 is accomplished through rational protecting group manipulations of commercially available monosaccharides and stereoselective glycosylations. The target tetrasaccharide in the form of its 2-aminoethyl glycoside is obtained in ∼24% yield over 10 steps following a linear strategy. The structure is particularly suitable for further glycoconjugate formation through the terminal free amine without hampering the reducing end stereochemistry.

Chemical O-Glycosylations: An Overview

The development of glycobiology relies on the sources of particular oligosaccharides in their purest forms. As the isolation of the oligosaccharide structures from natural sources is not a reliable option for providing samples with homogeneity, chemical means become pertinent. The growing demand for diverse oligosaccharide structures has prompted the advancement of chemical strategies to stitch sugar molecules with precise stereo- and regioselectivity through the formation of glycosidic bonds. This Review will focus on the key developments towards chemical O-glycosylations in the current century. Synthesis of novel glycosyl donors and acceptors and their unique activation for successful glycosylation are discussed. This Review concludes with a summary of recent developments and comments on future prospects.

Plesiomonas shigelloides Revisited

After many years in the family Vibrionaceae, the genus Plesiomonas, represented by a single species, P. shigelloides, currently resides in the family Enterobacteriaceae, although its most appropriate phylogenetic position may yet to be determined. Common environmental reservoirs for plesiomonads include freshwater ecosystems and estuaries and inhabitants of these aquatic environs. Long suspected as being an etiologic agent of bacterial gastroenteritis, convincing evidence supporting this conclusion has accumulated over the past 2 decades in the form of a series of foodborne outbreaks solely or partially attributable to P. shigelloides. The prevalence of P. shigelloides enteritis varies considerably, with higher rates reported from Southeast Asia and Africa and lower numbers from North America and Europe. Reasons for these differences may include hygiene conditions, dietary habits, regional occupations, or other unknown factors. Other human illnesses caused by P. shigelloides include septicemia and central nervous system disease, eye infections, and a variety of miscellaneous ailments. For years, recognizable virulence factors potentially associated with P. shigelloides pathogenicity were lacking; however, several good candidates now have been reported, including a cytotoxic hemolysin, iron acquisition systems, and lipopolysaccharide. While P. shigelloides is easy to identify biochemically, it is often overlooked in stool samples due to its smaller colony size or relatively low prevalence in gastrointestinal samples. However, one FDA-approved PCR-based culture-independent diagnostic test system to detect multiple enteropathogens (FilmArray) includes P. shigelloides on its panel. Plesiomonads produce β-lactamases but are typically susceptible to many first-line antimicrobial agents, including quinolones and carbapenems.

Convergent synthesis of the hexasaccharide related to the repeating unit of the O-antigen from E. coli O120

The hexasaccharide repeating unit of the O-antigen from E. coli O120 has been synthesized in the form of its 4-methoxyphenyl glycoside by a convergent [2 + 4] strategy.