Synthesis of α-d-glucosyl substituted methyl glycosides of 3-deoxy-α-d-manno- and d-glycero-α-d-talo-oct-2-ulosonic acid (Kdo/Ko) corresponding to inner core fragments of Acinetobacter lipopolysaccharide

Synthetic Optimizations for Gram-Scale Preparation of 1-O-Methyl d-Glycero-α-d-gluco-heptoside 7-Phosphate from d-Glucose

Heptose phosphates—unique linkers between endotoxic lipid A and O-antigen in the bacterial membrane—are pathogen-associated molecular patterns recognized by the receptors of the innate immune system. Understanding the mechanisms of immune system activation is important for the development of therapeutic agents to combat infectious diseases and overcome antibiotic resistance. However, in practice, it is difficult to obtain a substantial amount of heptose phosphates for biological studies due to the narrow scope of the reported synthetic procedures. We have optimized and developed an inexpensive and convenient synthesis for the first performed gram-scale production of 1-O-methyl d-glycero-α-d-gluco-heptoside 7-phosphate from readily available d-glucose. Scaling up to such amounts of the product, we have increased the efficiency of the synthesis and reduced the number of steps of the classical route through the direct phosphorylation of the O⁶,O⁷-unprotected heptose. The refined method could be of practical value for further biological screening of heptose phosphate derivatives.

Antigen binding by conformational selection in near-germline antibodies

Conformational flexibility in antibody-combining sites has been hypothesized to facilitate polyspecificity toward multiple unique epitopes and enable the limited germline repertoire to match an overwhelming diversity of potential antigens; however, elucidating the mechanisms of antigen recognition by flexible antibodies has been understandably challenging. Here, multiple liganded and unliganded crystal structures of the near-germline anticarbohydrate antibodies S25–2 and S25–39 are reported, which reveal an unprecedented diversity of complementarity-determining region H3 conformations in apparent equilibrium. These structures demonstrate that at least some germline or near-germline antibodies are flexible entities sensitive to their chemical environments, with conformational selection available as an evolved mechanism that preserves the inherited ability to recognize common pathogens while remaining adaptable to new threats.

(2-Ketulosonyl)onate 2,3-O-thionocarbonate donors for the synthesis of KO and KDO α-glycosides and a one-pot glycosylation method for 2-keto acid donors

Bifunctional (2-ketulosonyl)onate thionocarbonates are effective donors for the synthesis of KO and KDO α-glycosides with perfect control in stereoselectivity.

Synthesis of 5-O-oligoglucosyl extended α-(2→4)-Kdo disaccharides corresponding to inner core fragments of Moraxellaceae lipopolysaccharides

The heptose-deficient inner core of the lipopolysaccharide of several pathogenic strains of the Moraxellaceae family (Moraxella, Acinetobacter) and of Bartonella henselae, respectively, comprises an α-D-glucopyranose attached to position 5 of Kdo. In continuation of the synthesis of fragments of Acinetobacter haemolyticus LPS, the branched α-Glcp-(1 → 5)[α-Kdo-(2 → 4)]-α-Kdo trisaccharide motif was elaborated. The glycosylation of a suitably protected, α-(2 → 4)-interlinked Kdo-disaccharide was achieved in high yield and fair anomeric selectivity using a 4,6-O-benzylidene N-phenyltrifluoroacetimidate glucosyl donor. Subsequent regioselective reductive benzylidene opening afforded a trisaccharide acceptor, which was extended with β-D-glucopyranosyl and isomaltosyl residues. Global deprotection provided tri- to pentasaccharide structures corresponding to the inner core region of A. haemolyticus lipopolysaccharide.

Investigation on the Synthesis of Shigella flexneri Specific Oligosaccharides Using Disaccharides as Potential Transglucosylase Acceptor Substrates

Chemo-enzymatic strategies hold great potential for the development of stereo- and regioselective syntheses of structurally defined bioactive oligosaccharides. Herein, we illustrate the potential of the appropriate combination of a planned chemo-enzymatic pathway and an engineered biocatalyst for the multistep synthesis of an important decasaccharide for vaccine development. We report the stepwise investigation, which led to an efficient chemical conversion of allyl α-d-glucopyranosyl-(1→4)-α-l-rhamnopyranosyl-(1→3)-2-deoxy-2-trichloroacetamido-β-d-glucopyranoside, the product of site-specific enzymatic α-d-glucosylation of a lightly protected non-natural disaccharide acceptor, into a pentasaccharide building block suitable for chain elongation at both ends. Successful differentiation between hydroxyl groups features the selective acylation of primary alcohols and acetalation of a cis-vicinal diol, followed by a controlled per-O-benzylation step. Moreover, we describe the successful use of the pentasaccharide intermediate in the [5 + 5] synthesis of an aminoethyl aglycon-equipped decasaccharide, corresponding to a dimer of the basic repeating unit from the O-specific polysaccharide of Shigella flexneri 2a, a major cause of bacillary dysentery. Four analogues of the disaccharide acceptor were synthesized and evaluated to reach a larger repertoire of O-glucosylation patterns encountered among S. flexneri type-specific polysaccharides. New insights on the potential and limitations of planned chemo-enzymatic pathways in oligosaccharide synthesis are provided.