Expeditious Synthesis of C-Glycosyl Barbiturate Ligands of Bacterial Lectins: From Monomer Design to Glycoclusters and Glycopolymers

Abstract

The approach developed here offers a straightforward and efficient access to -C-glycosyl barbiturates ligands, spanning from glycomimetics to multivalent C-neoglycoconjugates, with the aim of deciphering structural parameters impacting the binding to pathogenic lectins. We reinvestigated the Knoevenagel condensation of barbituratic acid on protecting-group free carbohydrates and successfully designed sodium and 5,5-disubstituted N,N-dimethyl barbiturate forms of D-galactose, Lfucose, melibiose, 2'-fucosyllactose, maltose and evaluated their binding affinity by isothermal titration calorimetry with LecA (galactose-binding lectin) and LecB (fucose-binding lectin) from Pseudomonas aeruginosa and RSL (fucose-binding lectin) from Ralstonia solanacearum. The barbiturate ring was shown detrimental for binding to LecA (K D in mM range) and even more to LecB (non-interaction) while RSL is much more tolerant especially in presence of an aromatic group (K D in M range). However, distancing the barbiturate ring from the recognition carbohydrate residue by using oligosaccharides increased affinity up to low micromolar range. Extension of our convenient synthetic approach led in two-steps to melibiose-based C-glycosyl barbiturates clusters and C-glycosyl barbiturate glycopolymers exhibiting a dramatic enhancement of binding avidity for LecA.

N,N′‐Disubstituted Barbituric Acid: A Versatile and Modular Multifunctional Platform for Obtaining β‐C‐Glycoconjugates from Unprotected Carbohydrates in Water

“…The experimental ITC data (see SI) evidenced that galactosyl monosaccharides whether the monovalent 26 or the divalent 28 ones, do not interact with PNA. These results confirmed our recent observation revealed that the presence of the barbituric ring directly linked to the recognition carbohydrate is detrimental for the related lectin binding relying on steric hindrances. However, the interaction could be restored by using oligosaccharides enabling distance of the recognition carbohydrate from the barbituric ring.…”

“…Advantageously, the Knoevenagel condensation was performed in water at neutral pH and led to sodium salt of β‐ C ‐glycosylbarbiturates in excellent yields. In continuation of our long‐term program of chemo‐selective synthesis of (neo)glyconconjugates with the ultimate goal of facilitating the development of glycosciences, we were interested in exploring barbituric acid‐mediated Knoevenagel condensation and determined structural parameters of β‐ C ‐glycosylbarbiturates required for the interaction with pathogenic lectins …”

Supramolecular carbohydrate-based hydrogels from oxidative hydroxylation of amphiphilic β-C-glycosylbarbiturates and α-glucosidase-induced hydrogelation

“…1). A survey of the literature indicated that reactions of (i) bromination, 19 (ii) alkylation, 20,21 (iii) hydroxymethylation, 22 (iv) malonyl peroxide-mediated oxidation, 23 and (v) oxidative hydroxylation could be envisioned. Keeping in mind that green chemistry approaches should be favored, we took the route of oxidative hydroxylation 24 that occurs in water.…”

Enzymatic Synthesis of 2-(β-Galactosyl)-ethyl Methacrylate by β-Galactosidase fromPyrococcus woeseiand Application for Glycopolymer Synthesis and Lectin Studies

“…Glycopolymers can ideally mimic natural multivalent glycoconjugates and thus offer a platform to tailor multivalences for lectin binding with high affinity and avidity − or the design of toxin scavengers and inhibitors − and biosensors. − Important factors for the binding efficiency of glycopolymers are the glycan density and the polymer backbone itself. Chemical synthesis of glycan-containing monomers has seen significant progress in recent years. − However, chemical synthesis remains challenging and affords multiple reaction steps, resulting in moderate overall product yields. ,, In contrast, enzymatic synthesis offers a viable alternative to chemical synthesis. For the enzymatic synthesis of glycosylated monomers for later use in polymerization experiments, mainly hydrolases, such as lipases, proteases, or glycosidases, have been used. − Lipases catalyze the transesterification of divinyl esters with the terminal alcohol at the C-6 position of monosaccharides in organic solvents.…”