Caroline Nugier-Chauvin

Recent knowledge and innovations related to hexofuranosides: structure, synthesis and applications

Hexofuranosides are widely spread in nature, and notably in numerous pathogenic microorganisms. This particular five-membered ring for hexosides leads to novel biological properties and, as usual in glycochemistry, to completely different reactivity and selectivity. Far from being exhaustive, this review will first focus on the structure of the oligosaccharidic part of hexofuranosyl conjugates found in natural sources. Original syntheses will then be presented, stressing more particularly on the development of chemical and chemo-enzymatic tools for the access to 1,2-trans or 1,2-cis linkages. Finally, innovative applications related to biological, chemical and physicochemical fields for both natural and synthetic hexofuranosyl compounds will be described.

Synergistic relationships in algal-bacterial microcosms for the treatment of aromatic pollutants.

The potential of algal-bacterial microcosms was studied for the biodegradation of salicylate, phenol and phenanthrene. The isolation and characterization of aerobic bacterial strains capable of mineralizing each pollutant were first conducted. Ralstonia basilensis was isolated for salicylate degradation, Acinetobacter haemolyticus for phenol and Pseudomonas migulae and Sphingomonas yanoikuyae for phenanthrene. The green alga Chlorella sorokiniana was then cultivated in the presence of the pollutants at different concentrations, showing increasing inhibitory effects in the following order: salicylate < phenol < phenanthrene. The synergistic relationships in the algal-bacterial microcosms were clearly demonstrated, since for the three contaminants tested, a substantial removal (>85%) was recorded only in the systems inoculated with both algae and bacteria and incubated under continuous lighting. This study presents, to our knowledge, the first reported case of photosynthesis-enhanced biodegradation of toxic aromatic pollutants by algal-bacterial microcosms in a one-stage treatment.

Natural Glycans and Glycoconjugates as Immunomodulating Agents

Covering: up to the end of 2010 This review focuses on recent discoveries performed in the field of glycans and related glycoconjugates that have demonstrated immunomodulatory activities. Their tremendous potential for application, as well as some limitations, are also described.

Specific and non-specific enzymes for furanosyl-containing conjugates: biosynthesis, metabolism, and chemo-enzymatic synthesis.

There is no doubt now that the synthesis of compounds of varying complexity such as saccharides and derivatives thereof continuously grows with enzymatic methods. This review focuses on recent basic knowledge on enzymes specifically involved in the biosynthesis and degradation of furanosyl-containing polysaccharides and conjugates. Moreover, and when possible, biocatalyzed approaches, alternative to standard synthesis, will be detailed in order to strengthen the high potential of these biocatalysts to go further with the preparation of rare furanosides. Interesting results will be also proposed with chemo-enzymatic processes based on nonfuranosyl-specific enzymes.

Enzymatic synthesis of oligo-D-galactofuranosides and L-arabinofuranosides: from molecular dynamics to immunological assays

D-Galactofuranosyl-containing conjugates are ubiquitous in many pathogenic microorganisms, but completely absent from mammals. As they may constitute interesting pharmacophores, recent works have been dedicated to their preparation. Besides well-reported chemical procedures, enzymatic approaches are still limited, mainly due to the lack of the corresponding biocatalysts. Based on the similarity between chemical structures, the arabinofuranosyl hydrolase Araf51 from Clostridium thermocellum was expected to recognize both the L-Araf motif and its D-Galf analogue. Molecular dynamics and STD-NMR were firstly used to confirm this hypothesis and increase our knowledge of the active site. Interestingly, this arabinofuranosidase was not only able to hydrolyze galactosyl derivatives, but was also really efficient in catalyzing oligomerisations using p-nitrophenyl furanosides as donors. The structures of the products obtained were determined using mass spectrometry and NMR. Amongst them, all the possible regioisomers of di-arabino and -galactofuranosides were synthesized, and the ratio of each regioisomer was easily tuned with respect to the reaction time. Especially, the galactofuranobioside displaying the biologically relevant sequence beta-D-Galf-(1,6)-beta-D-Galf was enzymatically prepared for the first time. All fractions going from di- to penta-arabino- and galactofuranosides were tested for their ability in eliciting the production of TNF-alpha. Interesting immunological properties were observed with arabinofuranosides as short as three sugar residues.

Probing UDP-galactopyranose mutase binding pocket : A dramatic effect on substitution of the 6-position of UDP-galactofuranose

UDP-galactopyranose mutase (UGM) catalyzes the isomerization of UDP-galactopyranose (UDP-Galp) into UDP-galactofuranose (UDP-Galf), an essential step of the mycobacterial cell wall biosynthesis. UDP-(6-deoxy-6-fluoro)-D-galactofuranose 1 was tested as substrate of UGM. Turnover could be observed by HPLC. The k(cat) (7.4s(-1)) and the K(m) (24 mM) of 1 were thus measured and compared with those of UDP-Galf and other fluorinated analogs. The presence of the fluorine atom at the 6-position had a moderate effect on the rate of the reaction but a huge one on the interactions between the enzyme and its substrate. This result demonstrated that key interactions occur at the vicinity of the 6-position of UDP-galactose in the Michaelis complex.

Engineering Ribonucleoside Triphosphate Specificity in a Thymidylyltransferase

Natures glycosylation catalysts, glycosyltransferases, indirectly manipulate and control many important biological processes by transferring sugar nucleotide donors onto acceptors. Challenging chemical synthesis impedes synthetic access to sugar nucleotides and limits the study of many glycosyltransferases. Enzymatic access to sugar nucleotides is a rapidly expanding avenue of research, limited only by the substrate specificity of the enzyme. We have explored the promiscuous thymidylyltransferase from Streptococcus pneumoniae, Cps2L, and enhanced its uridylyltransferase and guanidyltransferase activities by active site engineering. Mutagenesis at position Q24 resulted in a variant with 10-, 3-, and 2-fold enhancement of UDP-glucosamine, UDP-mannose, and UDP- N-acetylglucosamine production, respectively. New catalytic activities were observed for the Cps2L variant over the wild-type enzyme, including the formation of GDP-mannose. The variant was evaluated as a catalyst for the formation of a series of dTDP- and UDP-furanoses and notably produced dTDP-Gal f in 90% yield and UDP-Ara f in 30% yield after 12 h. A series of 3- O-alkylglucose 1-phosphates were also evaluated as substrates, and notable conversions to UDP-3- O-methylglucose and UDP-3- O-dodecylglucose were achieved with the variant but not the wild-type enzyme. The Q24S variant also enhanced essentially all thymidylyltransferase activities relative to the wild-type enzyme. Comparison of active sites of uridylyltransferases and thymidylyltransferases with products bound indicate the Q24S variant to be a new approach in broadening nucleotidylyltransferase activity.

NMR Stereochemical analysis of chiral alkylsulfoxides with α-methoxyaryl acetic acids

Abstract (S)-α-methoxyphenyl and (S)-α-methoxy-2-naphtyl acetic acids (MPA and 2-NMA) were used as NMR chiral shift reagents for the stereochemtical analysis of alkylsulfoxides. It was shown that the use of C 6 D 6 as NMR solvent increased the magnitude of the observed effects for both 1 H- and 13 C-NMR spectra. Moreover, 2-NMA led to a much longer range effect on the chain but lowered the signal spliting of the α-methylene groups.

Probing β-(1→3)-d-glucans interactions with recombinant human receptors using high-resolution NMR studies

A full characterization of the high-resolution NMR spectrum of the laminarihexaose is described and used for the determination of the binding epitope of the more complex but structurally related laminarin. These biophysical data extend the current knowledge of β-glucans/Dectin-1 interactions and suggest different biological mechanisms in close relation with the size of the saccharidic chain.

Enantiomeric excess determination of some chiral sulfoxides by NMR: use of (S)-Ibuprofen® and (S)-Naproxen® as shift reagents

Abstract The well known drugs (S)-Ibuprofen and (S)-Naproxen were used as NMR shift reagents for the stereochemical analysis of alkylsulfoxides. It was shown that (S)-Naproxen could be worthwhile substituted to (S)-MPA or (S)-2-NMA for the stereochemical analysis of some chiral alkyl sulfoxides.