Murielle Muzard

Enzymatic synthesis of alkyl β-D-xylosides and oligoxylosides from xylans and from hydrothermally pretreated wheat bran

Direct and efficient preparation of pentyl and octyl β-D-xylosides and oligoxylosides has been achieved from xylans and n-pentanol or n-octanol in aqueous medium with xylanases. The method has been successfully applied with xylooligosaccharides produced from hydrothermally pretreated wheat bran to produce octyl oligoxylosides. The pentose-based surfactants thus obtained exhibit good surface properties compared to other alkyl glycosides. These molecules represent interesting candidates for the production of new green surfactants.

Fluorophosphonylated Nucleoside Derivatives as New Series of Thymidine Phosphorylase Multisubstrate Inhibitors

The synthesis of new class of potential TPase inhibitors containing a difluoromethylphosphonate function as phosphate mimic is reported. This new series was prepared from a readily available fluorinated building block in few steps. Two series were evaluated as potential inhibitors: a linear series and a conformational constrained series. The activity of these multisubstrate inhibitors depends on the size of the spacer introduced between the pyrimidine ring and the phosphonate function. Best results were observed from triazolyl derivatives, easily obtained from propargylthymine and corresponding azides.

β-Xylopyranosides: synthesis and applications

D-Xylose is the main constituent of hemicelluloses, the second most abundant polysaccharide in nature after cellulose. Thus, the β-xylopyranose motif is widely distributed in the plant kingdom. On the contrary, D-xylose is an unusual carbohydrate in mammalian cells, only present in the structures of proteoglycans, macromolecules with important biological functions. In recent years, β-xylopyranosides have attracted renewed interest due to the development of biomass-derived molecules and their numerous applications. In this review, we will first focus on general routes for the preparation of β-xylopyranosides according to the nature of the glycosidic linkage and the aglycone moiety by chemical and enzymatic pathways. The main uses of these molecules for different applications, such as activators in the biosynthesis of glycosaminoglycans, for enzyme inhibition and as surfactants will be presented.

Chemoenzymatic synthesis of “click” xylosides and xylobiosides from lignocellulosic biomass

Synthesis of bio-based molecules from plant biomass with chemoenzymatic pathways represents a challenging task for the development of green chemistry. In this context, an efficient two-step chemoenzymatic sequence has been achieved for the preparation of triazole-linked xylosides and xylobiosides from biomass-derived xylans. The synthesis of propargyl xyloside and xylobioside catalysed by a xylanase in an aqueous medium was first studied and improved according to different reaction parameters. Cycloaddition reactions between the terminal alkyne moiety of these xylosides or xylobiosides and various aliphatic, aromatic or functionalized azides (“click chemistry”) afforded various triazole-linked O-xylosides and O-xylobiosides in high yields. These molecules are of interest for different biological applications.

'Click'-xylosides as initiators of the biosynthesis of glycosaminoglycans: Comparison of mono-xylosides with xylobiosides.

Different mono‐xylosides and their corresponding xylobiosides obtained by a chemo‐enzymatic approach featuring various substituents attached to a triazole ring were probed as priming agents for glycosaminoglycan (GAG) biosynthesis in the xylosyltransferase‐deficient pgsA‐745 Chinese hamster ovary cell line. Xylosides containing a hydrophobic aglycone moiety were the most efficient priming agents. Mono‐xylosides induced higher GAG biosynthesis in comparison with their corresponding xylobiosides. The influence of the degree of polymerization of the carbohydrate part on the priming activity was investigated through different experiments. We demonstrated that in case of mono‐xylosides, the cellular uptake as well as the affinity and the catalytic efficiency of β‐1,4‐galactosyltransferase 7 were higher than for xylobiosides. Altogether, these results indicate that hydrophobicity of the aglycone and degree of polymerization of glycone moiety were critical factors for an optimal priming activity for GAG biosynthesis.

Exploring the aglycone subsite of a GH11 xylanase for the synthesis of xylosides by transglycosylation reactions

Xylanases Tx-xyn10 and Tx-xyn11 were compared for their transxylosylation abilities in the presence of various acceptors. Tx-xyn10 exhibited a broad specificity for various acceptors, whereas xylanase Tx-xyn11 catalysed transxylosylation reactions only in presence of polyphenolic acceptors. A modelling approach was developed to study the molecular bottlenecks into the active site of the enzyme that could be responsible for this restricted specificity. The glycosyl-enzyme intermediate of Tx-xyn11 was modelled, and a rotamer of the Y78 residue was integrated. In silico mutations of some residues from the (+1) and (+2) subsites were tested for the deglycosylation step in the presence of non-polyphenolic acceptors. The results indicated that the mutant W126A was able to use aliphatic alcohols and benzyl alcohol as acceptors for transxylosylation. Experimental validation was tested by mutating the xylanase Tx-xyn11 at position W126 into alanine. The specific activity and catalytic efficiency of the W126A mutant during the hydrolysis of xylans decreased by 2-fold and 4-fold, respectively, compared to wild-type xylanase. Among tested acceptors, transxylosylation catalysed by mutant W126A was improved with benzyl alcohol leading to a 2-fold higher concentration of benzyl xylobioside, as predicted by in silico mutation. This improved transxylosylation in the presence of benzyl alcohol leading to higher synthesis of benzyl xylobioside could likely be explained by lowest steric hindrance in the aglycone subsite of the mutated xylanase. No secondary hydrolysis of benzyl xylobioside occurred for both wild-type and mutant xylanases. Finally, our results demonstrated that the modelling approach was limited and that accounting for protein dynamics can lead to improved models.

d-Xylose and l-arabinose laurate esters: Enzymatic synthesis, characterization and physico-chemical properties

Efficient enzymatic synthesis of d-xylose and l-arabinose lauryl mono- and diesters has been achieved by transesterification reactions catalysed by immobilized Candida antarctica lipase B as biocatalyst, in organic medium in the presence of d-xylose or l-arabinose and vinyllaurate at 50 °C. In case of l-arabinose, one monoester and one diester were obtained in a 57% overall yield. A more complex mixture was produced for d-xylose as two monoesters and two diesters were synthesized in a 74.9% global yield. The structures of all these pentose laurate esters was solved. Results demonstrated that the esterification first occurred regioselectively onto the primary hydroxyl groups. Pentose laurate esters exhibited interesting features such as low critical aggregation concentrations values all inferior to 25 μM. Our study demonstrates that the enzymatic production of l-arabinose and d-xylose-based esters represents an interesting approach for the production of green surfactants from lignocellulosic biomass-derived pentoses.