913060-93-2Relevant articles and documents
Total Synthesis of the Repeating Unit of Bacteroides fragilis Zwitterionic Polysaccharide A1
Pathan, Ennus K.,Ghosh, Bhaswati,Podilapu, Ananda Rao,Kulkarni, Suvarn S.
, p. 6090 - 6099 (2021/05/06)
Zwitterionic polysaccharides isolated from commensal bacteria are endowed with unique immunological properties and are emerging as immunotherapeutic agents as well as vaccine carriers. Reported herein is a total synthesis of the repeating unit of Bacteroides fragilis zwitterionic polysaccharide A1 (PS A1). The structurally complex tetrasaccharide unit contains a rare sugar 2-acetamido-4-amino-2,4,6-trideoxy-d-galactose (AAT) and two consecutive 1,2-cis glycosidic linkages. The repeating unit was efficiently assembled by rapid synthesis of d-galactosamine and AAT building blocks from cheap and abundant d-mannose via a one-pot SN2 displacement of 2,4-bistriflates and installation of all of the glycosidic bonds in a highly stereoselective manner. The total synthesis involves a longest linear sequence of 17 steps with 3.47% overall yield.
Practical approach for the stereoselective introduction of β-arabinofuranosides
Zhu, Xiangming,Kawatkar, Sameer,Rao, Yu,Boons, Geert-Jan
, p. 11948 - 11957 (2007/10/03)
A practical approach for the stereoselective introduction of β-arabinofuranosides has been developed on the basis of locking an arabinosyl donor in a conformation in which nucleophilic attack from the β face is favored. The new glycosyl donor was designed by analyzing optimized geometries of low-energy conformers of the arabinofuranosyl oxacarbenium ion. The Newman projection of the E3 conformer indicated that nucleophilic attack from the α face is disfavored because an eclipsed H-2 will be encountered. On the other hand, an approach from the β face was expected to be more favorable, because it will experience only staggered substituents. The arabinofuranosyl oxacarbenium ion could be locked in the E3 conformation by employing a 3,5-O-di-tert-butylsilane protecting group, which places C-5 and O-3 in a pseudoequatorial orientation, resulting in a perfect chair conformation of the protecting group. The new glycosyl donor gave excellent β selectivities in a range of glycosylations with glycosyl acceptors having primary and secondary alcohols. The attractiveness of the new methodology was demonstrated by the chemical synthesis of a fragment of arabinogalactan, which is an important constituent of the primary plant cell wall.