# Synthesis of the Tetrasaccharide Repeating Unit from Klebsiella pneumoniae Serotype K2 Capsular Polysaccharide

## TL;DR

This paper describes the synthesis of two tetrasaccharides from the K2 capsular polysaccharide of Klebsiella pneumoniae, useful for immunological and structural studies.

## Contribution

A successful sequential glycosylation strategy was developed to synthesize modified tetrasaccharides with specific structural challenges.

## Key findings

- A convergent [2 + 2] glycosylation approach failed due to C-2 inversion issues.
- A sequential glycosylation method successfully produced both tetrasaccharides.
- The developed route allows for the synthesis of analogs with structural modifications.

## Abstract

Described is the
synthesis of the two tetrasaccharides (1 and 2) related to the repeating unit from the Klebsiella
pneumoniae Serotype K2 capsular polysaccharide.
The compounds differ by the presence or absence of an acetate ester
on O-2 of the mannopyranose residue of the repeating unit. Κey
challenges in the synthesis were the installation of three 1,2-cis glycosidic linkages, including a β-mannopyranoside,
the selective introduction of an α-d-glucuronic acid
residue, and the late-stage incorporation of an acetate ester in 2. A convergent approach employing a key [2 + 2] glycosylation
was initially explored, but the key C-2 inversion needed to install
the β-mannopyranoside in the resulting tetrasaccharide failed.
An alternative strategy, using a sequential glycosylation approach,
was successful in providing both targets. The developed route can
be adapted to provide analogs containing other modifications. Such
compounds are useful probes for immunological and structural biology
investigations.