A Hitchhiker's Guide to Problem Selection in Carbohydrate Synthesis

A Fluorinated Sialic Acid Vaccine Lead Against Meningitis B and C

Inspired by the specificity of α-(2,9)-sialyl epitopes in bacterial capsular polysaccharides (CPS), a doubly fluorinated disaccharide has been validated as a vaccine lead against Neisseria meningitidis serogroups C and/or B. Emulating the importance of fluorine in drug discovery, this molecular editing approach serves a multitude of purposes, which range from controlling α-selective chemical sialylation to mitigating competing elimination. Conjugation of the disialoside with two carrier proteins (CRM197 and PorA) enabled a semisynthetic vaccine to be generated; this was then investigated in six groups of six mice. The individual levels of antibodies formed were compared and classified as highly glycan-specific and protective. All glycoconjugates induced a stable and long-term IgG response and binding to the native CPS epitope was achieved. The generated antibodies were protective against MenC and/or MenB; this was validated in vitro by SBA and OPKA assays. By merging the fluorinated glycan epitope of MenC with an outer cell membrane protein of MenB, a bivalent vaccine against both serogroups was created. It is envisaged that validation of this synthetic, fluorinated disialoside bioisostere as a potent antigen will open new therapeutic avenues.

Chemical Synthesis Creates Single Glycoforms of the Ectodomain of Herpes Simplex Virus-1 Glycoprotein D

Herpes simplex virus-1 (HSV-1) utilizes multiple viral surface glycoproteins to trigger virus entry and fusion. Among these glycoproteins, glycoprotein D (gD) functions as a receptor-binding protein, which makes it an attractive target for the development of vaccines against HSV-1 infection. Several recombinant gD subunit vaccines have been investigated in both preclinical and clinical phases with varying degrees of success. It is fundamentally critical to explore the functions of gD glycans. In light of this, we report an efficient synthetic platform to construct glycosylated gDs bearing homogeneous glycans at N94 and N121. The oligosaccharides were prepared by enzymatic synthesis and conjugated to peptidyl sectors. The glycoproteins were constructed via a combination of 7-(piperazin-1-yl)-2-(methyl)quinolinyl (PPZQ)-assisted expressed protein ligation and β-mercapto amino acid-assisted-desulfurization strategies. Biological studies showed that synthetic gDs exhibited potent in vivo activity in mice.

On the influence of solvent on the stereoselectivity of glycosylation reactions

Methodology development in carbohydrate chemistry entails the stereoselective formation of C-O bonds as a key step in the synthesis of oligo- and polysaccharides. The anomeric selectivity of a glycosylation reaction is affected by a multitude of parameters, such as the nature of the donor and acceptor, activator/promotor system, temperature and solvent. The influence of different solvents on the stereoselective outcome of glycosylation reactions employing thioglucopyranosides as glycosyl donors with a non-participating protecting group at position 2 has been studied. A large change in selectivity as a function of solvent was observed and a correlation between selectivity and the Kamlet-Taft solvent parameter π* was found. Furthermore, molecular modeling using density functional theory methodology was conducted to decipher the role of the solvent and possible reaction pathways were investigated.