Expedient Synthesis of the Pentasaccharide Repeating Unit of the Polysaccharide O‐Antigen of Escherichia coli O11

Abstract

A convergent [3+2] block synthetic strategy was developed for the synthesis of the pentasaccharide repeating unit of the cell wall O‐antigen of Escherichia coli O11 strain in excellent yield in a minimum number of steps. Several suitably functionalized thioglycoside derivatives were used as glycosyl donors during the synthesis of the target compound. A thioglycoside was the glycosyl donor used to couple with another thioglycoside derivative in a highly stereoselective manner exploiting the difference of their reactivity profile. A combination of Niodosuccinimide (NIS) and perchloric acid supported over silica gel (HClO4−SiO2) was used as a thiophilic glycosylation activator system in all stereoselective glycosylation reactions. HClO4−SiO2 acted as a user‐friendly solid acid catalyst. Yields were very good in all glycosylation steps with a high stereoselective outcome. The synthetic pentasaccharide could be coupled to an appropriate protein to furnish a glycoconjugate derivative for its use in immunochemical studies.

Determination of the Structural Integrity and Stability of Polysialic Acid during Alkaline and Thermal Treatment

“…Production processes for polysaccharides from natural sources suffer from difficulties in the extraction and purification of the product [24]. A further disadvantage lies in the batch-dependent variations in size and the related chain length of the polysaccharides [25]. A promising approach for the synthesis of polysaccharides with defined chain lengths is the cleavage of long-chain material through controlled enzymatic or thermal hydrolysis [26,27].…”

Systematic chemoenzymatic synthesis of O-sulfated sialyl Lewis x antigens

“… 27 Initial attempts to glycosylate acceptors 15 and 16 in dichloromethane with 1.2 equivalents of thiophenyl fucoside 14 produced trisaccharides in alpha and beta mixtures. In contrast, stereospecific formation of trisaccharides was achieved when a mixed solvent of diethylether and dichloromethane (1 : 1) 50 , 51 was employed. The reaction of acceptors 15 and 16 with 1.2 equivalents of fucosyl donor 14 produced compounds 17 and 18 in 68% and 65% yields, respectively.…”

Glycoconjugate vaccines: some observations on carrier and production methods

“…Another strategy has been to produce polysaccharides synthetically in blocks. The exact number can vary, such as a di-and tetra-saccharides (Budhadev & Mukhopadhyay, 2015), di-and tri-saccharides (Mandal, 2014;Mondal, Liao, Mondal, & Guo, 2015;Si & Misra, 2016), three disaccharides (Scott et al, 2016) and two tri-saccharides (Seeberger, Pereira, & Govindan, 2017). However, it should be noted that it is possible to compare assembly methods and one study revealed that linear assembly may be more effective than block assembly (Dhara & Misra, 2015;Seeberger et al, 2017).…”