Semi-Synthetic Glycoconjugate Vaccine Lead Against Acinetobacter baumannii 17978

Abstract

Acinetobacter baumannii is a opportunistic bacterial pathogen responsible for serious nosocomial infections that is becoming increasingly resistant against antibiotics. Capsular polysaccharides (CPS) that cover A. baumannii are a major virulence factor that play an important role in pathogenesis, are used to assign serotypes and provide the basis for vaccine development. Synthetic oligosaccharides resembling the CPS of A. baumannii 17978 were printed onto microarray slides and used to screen sera from patients infected with A. baumannii as well as a monoclonal mouse antibody (mAb C8). A synthetic oligosaccharide emerged from glycan array screening as lead for the development of a vaccine against A. baumannii 17978. Tetrasaccharide 20 is a key epitope for recognition by an antibody and is a vaccine lead.

Keywords: Acinetobacter Baumannii; Carbohydrate; Glycans; Immunology; Total Synthesis.

Figure 1

A. baumannii CPS repeating units contain rare amino sugars.

Figure 2

A) Repeating unit of A. baumannii 17978 CPS and related oligosaccharides synthesized from building blocks 3–14; B) Structure of A. baumannii 17978 related glycans 15–30. TCA=trichloroacetyl; N₃=azide; Ac=acetyl; Bn=benzyl, Bz=benzoyl, TBS=tert‐butyldimethylsilyl, Nap=2‐naphthylmethyl; Lev=levulinyl; Fmoc=fluorenylmethyloxycarbonyl; Cbz=carboxybenzyl; Ph=phenyl.

Figure 3

A) Synthesis of tri‐, tetrasaccharides (19, 25); B) Attempted synthesis of pentasaccharide 15.

Figure 4

A) Efficient syntheses of pentasaccharides 15 and 16 using building blocks 5 and 11 followed by modification of the core of pentasaccharide fragment. B) Synthesis of tetrasaccharides 20 and 21 using direct glycosylation with diamino‐D‐glucuronate 12 building block.

Figure 5

Assembly of short oligosaccharides. A) Synthesis of trisaccharides 22 and 23. B) Synthesis of disaccharide 26 and monosaccharide 30.

Figure 6

Glycan array analysis of A. baumannii ATCC17978 oligosaccharides. A) Printing pattern of microarray and binding pattern of human serum to immobilized glycans. B) IgG antibody binding to glycans with sera from infected patients. A serum dilution of 1 : 100 was used. C) IgG antibody binding to glycans with the monoclonal mouse antibody C8. Dilutions of 1 : 50 and 1 : 100 of mAb C8 were used MFI, mean fluorescence in intensity (mean±standard deviation); PB, printing buffer; For glycan structures please see Figure 2B. D) Structure of the identified repeating unit.