Emerging Trends in Glycoscience, Part #1

L-Hexoses are a family of exceptionally rare, prohibitively expensive, and synthetically challenging sugars with great biological significance. Requiring access to L-iduronic acid building blocks for the construction of glycosaminoglycan mimetics, we have recently developed the “fluorine-directing effect” to rapidly access these compounds with high efficiency. Our strategy, which entails the stereoselective C-5 epimerisation of D-hexose derivatives, has been optimised for the construction of L-IdoA and L-idose glycosyl donors. Its success has also been understood with the aid of density functional theory (DFT) calculations. Herein we describe the harnessing of this chemistry to carve out new synthetic routes to other rare L-hexoses. These include the commercially unavailable L-alturonic acid, a component of the capsular polysaccharides of the pathogens A. viridans var. homi and P. mirabilis O10, and L-guluronic acid, a key component of alginates which are polysaccharides of considerable industrial importance.

Avian pathogenic Escherichia coli (APEC) O1 is one of the pathogens that cause significant economic losses to the poultry industry. Therefore, developing a vaccine is an urgent necessity because of concerns about the emergence of drug-resistant bacteria and zoonosis [1]. In this context, it has been reported that O antigen of APEC O1 LPS has an antigenicity, but the detailed antigenic glycan structure has not been elucidated yet. Herein we report the efficient synthesis and biological evaluation of glycoconjugates consisting of pentasaccharide repeating units of lipopolysaccharide (LPS) derived from E. coli O1 and BSA using our boron-mediated aglycon delivery (BMAD) method [2-4]. ELISA tests using the synthesized glycoconjugates and the APEC O1 immune chicken serum revealed that the pentasaccharide derived from E. coli O1A is a glycotope candidate of APEC O1, with great potential as an antigen for vaccine development [5,6].