Total Syntheses of Conjugation-Ready Trisaccharide Repeating Units of Pseudomonas aeruginosa O11 and Staphylococcus aureus Type 5 Capsular Polysaccharide for Vaccine Development

Abstract

Pseudomonas aeruginosa belongs to the group of three "critical priority" multi-drug-resistant pathogens listed by WHO and is responsible for severe and often deadly infections such as bloodstream infections and pneumonia. Staphylococcus aureus is also a "high priority" pathogen which is a major cause of serious nosocomial infections such as bacteremia, sepsis, and endocarditis. Owing to their ability to adapt resistance to almost any antibiotics, vaccines against these pathogens are urgently required. These pathogens express structurally unique and densely functionalized glycans on their surfaces which are absent on the host cells. Such carbohydrate antigens are valuable targets for the development of glycoconjugate vaccines and diagnostics. Here, we report the first total synthesis of the conjugation-ready trisaccharide repeating unit of Pseudomonas aeruginosa O11 via a highly stereoselective and efficient assembly of a rare Lfucosamine-and D-fucosamine-containing 1,2-cis-linked disaccharide motif and its regioselective glycosylation at O3. A systematic study was conducted for the notoriously difficult glycosylation with the most unreactive axial 4-OH of the rare disaccharide, and the successful outcome was utilized to accomplish the total synthesis of an aminopropyl linker-attached trisaccharide repeating unit of Staphylococcus aureus capsular polysaccharide type 5, which is also a potential antigen for immunotherapy and vaccine development. The judicious selection of protecting groups and reaction conditions allowed the stereoselective assembly and selective functional group interconversions to access the structurally complex linker-attached trisaccharide repeating units, which are valuable tools for immunological evaluation and vaccine development. The strategy is useful for the synthesis of other structurally related complex glycans.

Transfer learning enables the molecular transformer to predict regio- and stereoselective reactions on carbohydrates

“…We obtained similar prediction performances from both models when analyzing a recently published total syntheses of the trisaccharide repeating unit of Pseudomonas aeruginosa and Staphylococcus aureus 43 . Those synthetic sequences comprises four difficult regio-and stereoselective glycosylation steps and five regioselective protection steps that are of particular interest.…”

“…The USPTO data set derived from Lowe 12 that we used for training and evaluation, our carbohydrate reactions, as well as the ones from the work of Behera et al 43 are available from (https://github.com/rxn4chemistry/OpenNMT-py/tree/carbohydrate_transformer). Source data are provided with this paper.…”

“…Our assessment consists of a 14-step total synthesis of a modified substrate of a eukaryotic oligosaccharil transferase (OST). We also challenge our Carbohydrate Transformer to predict the reactions from the recently published total syntheses of the trisaccharide of Pseudomonas aeruginosa and Staphylococcus aureus 43 as a further assessment on more complex carbohydrate reactions. Those reactions would be considered challenging to predict, even for carbohydrate experts.…”

Conjugation of Synthetic Trisaccharide of Staphylococcus aureus Type 8 Capsular Polysaccharide Elicits Antibodies Recognizing Intact Bacterium

“…aureus CP5 and CP8 have been found as highly potent antigenic targets. To date, chemical synthesis of the trisaccharide repeating units of CP5 (Danieli et al, 2012;Yasomanee et al, 2016;Hagen et al, 2017;Behera et al, 2020) and CP8 (Visansirikul et al, 2015) has been achieved. The immunological mechanism remains unclear.…”

Chemical Synthesis and Immunological Evaluation of Helicobacter pylori Serotype O6 Tridecasaccharide O‐Antigen Containing a dd‐Heptoglycan

“…[20] Thechemical synthesis of the H. pylori O6A Oantigen tridecasaccharide and O6B O-antigen octasaccharide is essential for immunological identification of H. pyloriexpressing Le y tetrasaccharide and dd-heptoglycan. The chemical synthesis of H. pylori O6 O-antigen tridecasaccharide poses an umber of challenges,e specially the steric hindrance of dd-heptoglycan that influences glycosylation efficiencies.T oi mprove the yield of glycosylation reactions, an electronic-effect-based protecting-group strategy, [29,30] optimization of leaving group/activator conditions, [31] and steric-effect-based assembly sequence planning [32][33][34] served well to tune the reactivities of the glycosyl donor and acceptor.Here, we report the first total synthesis of H. pylori serotype O6A and O6B O-antigens by at rial-and-error approach based on the reactivities of the glycosyl donor and acceptor to prepare sterically hindered long-chain glycans.Glycan array screening identified the key epitopes that can be recognized by IgG antibodies against native LPS as ab asis for the design of synthetic carbohydrate conjugate vaccines. [35] Therefore, al ibrary of synthetic serotype O6 O-antigen fragments has been established for immunological investigations,p articularly to elucidate the antigenicity of the Le y oligosaccharide and dd-heptoglycan.…”