Enantioselective Crystallization of Diglycerol Dicarbonate: Impact of the Microstructure on Polyhydroxyurethane Properties.

Bicylic carbonates are precursors employed in non-isocyanate polyurethane syntheses, namely polyhydroxyurethanes (PHUs) and, among them, ether-activated biobased diglycerol dicarbonate (DGDC) is widely investigated. Herein, the original separation of DGDC stereoisomers, thanks to a recrystallization procedure, leading to enantiomers having different crystal lattices, that is, square transparent crystals and needle-like structures, respectively, is reported. In this study, the separation and the characterization of the two crystal structures is first discussed and, second, the impact of the stereochemistry of DGDC on the corresponding PHUs properties is investigated.

Synthesis and Self-Assembly of Xylan-Based Amphiphiles: From Bio-Based Vesicles to Antifungal Properties.

This work aims at designing functional biomaterials through selective chemical modification of xylan from beechwood. Acidic hydrolysis of xylan led to well-defined oligomers with an average of six xylose units per chain and with an aldehyde group at the reductive end. Reductive amination was performed on this aldehyde end group to introduce an azide reactive group. "Click chemistry" was then applied to couple these hydrophilic xylans moieties with different hydrophobic fatty acid methyl esters that were previously functionalized with complementary alkyne functions. The resulting amphiphilic bio-based conjugates were then self-assembled using three different methods, namely, direct solubilization, thin-film rehydration/extrusion, and microfluidics. Well-defined micelles and vesicles were obtained, and their high loading capacity with propiconazole as an antifungal active molecule was shown. The resulting vesicles loaded with propiconazole in a microfluidic process proved to significantly improve the antifungal activity of propiconazole, demonstrating the high potential of such xylan-based amphiphiles.

Versatile cross-linked fatty acid-based polycarbonate networks obtained by thiol-ene coupling reaction.

Bio-sourced polycarbonate networks have been synthesized from an alkene-functional fatty-acid based polycarbonate precursor. Cross-linked networks were created using the radical thiol-ene coupling reaction. The resulting polycarbonate materials exhibited versatile properties either influenced by the structure of the cross-linker or the cross-linker/olefin unit ratio. Indeed, the storage modulus above the glass transition temperature could be modulated from 0.9 to 8.9 MPa only by changing the type of cross-linker, i.e. 1,9-nonanedithiol vs. 1,4-benzenedimethanethiol. The cross-linker/olefin unit ratio was also shown to largely impact the polycarbonate networks properties. An elongation at break of nearly 200% was reached when a low cross-linker/olefin ratio was applied. Moreover, functional polycarbonate networks bearing pendant thiol groups were obtained when an excess of dithiol was used with respect to olefin groups.

Simple and Efficient Approach toward Photosensitive Biobased Aliphatic Polycarbonate Materials.

Fatty acids were used as precursors for the synthesis of photosensitive polycarbonate materials. In order to avoid multistep reactions, a simple and straightforward methodology toward the synthesis of photosensitive monomers has been developed. Hence, a fatty acid-based cyclic carbonate bearing an unsaturation was synthesized and subsequently polymerized in a controlled manner (D = 1.07) by organo-catalyzed ring-opening polymerization (ROP). A thio-cinnamate derivative was then readily synthesized via a one-pot reaction and grafted onto the polycarbonate backbone by thiol-ene reaction. The content of photoresponsive cinnamoyl moiety grafted on the polycarbonate was tunable with the reaction time. Such functionalized polycarbonates could be crosslinked (by UV irradiation at 365 nm) and partially decrosslinked (irradiated at 254 nm) and exhibit versatile properties ranging from rather tough materials to elastomeric networks with respect to the content of the photosensitive cinnamoyl moiety grafted on the polymer.

Bleaching Earths as Powerful Additives for Ru-Catalyzed Self-Metathesis of Non-Refined Methyl Oleate at Pilot Scale.

A practical and cost-effective ruthenium-catalyzed self-metathesis of non-refined methyl oleate (85 %) derived from very high oleic sunflower oils was demonstrated at pilot scale using a robust and kg-scale commercially available SIPr-M71 pre-catalyst. The simple addition of 1 wt % bleaching earths (Tonsil 110FF) to a thermally pretreated oil could efficiently prevent catalyst deactivation. Remarkably, without the need for filtration, the catalytic system was able to achieve a turnover number (TON) of more than 744 000 at a catalyst loading of only 1 ppm. At large scale (up to 200 kg), the equilibrium of the self-metathesis reaction was reached within 1 hour at 50 °C under neat conditions at a very low 5 ppm catalyst loading to produce the expected primary metathesis products (PMP), that is, 9-octadecene and dimethyl-9-octadecenoate, with a productive TON of 94900.

Periodate oxidation of 4-O-methylglucuronoxylans: Influence of the reaction conditions.

This work aims at studying the sodium periodate oxidation of 4-O-methylglucuronoxylans (MGX) in different experimental conditions for a control of the oxidation degree. A series of sodium periodate oxidation reactions were conducted at three NaIO4/xylose molar ratios: 0.05, 0.20 and 1.00. The effects of xylan molar mass, xylan concentration and reaction temperature on the reaction rate have been evaluated by UV/visible spectroscopy at 0.20 NaIO4/xylose ratio. No depolymerization is observed at 0.05 ratio while depolymerization occurs at 0.20 and is even complete at 1.00 NaIO4/xylose ratio. An increase of the reaction temperature - up to 80 °C - leads to an increase of the oxidation rate with no effect on the depolymerization. At high xylan concentrations, the oxidation rate increases but promotes chains aggregation.

Total synthesis and biological evaluation of the cytotoxic resin glycosides ipomoeassin A-F and analogues.

A multitasking C-silylation strategy using the readily available compound 26 as a surrogate for cinnamic acid represents the key design element of a total synthesis of all known members of the ipomoeassin family of resin glyosides. This protecting group maneuver allows the unsaturated acids decorating the glucose subunit of the targets to be attached at an early phase of the synthesis, prevents their participation in the ruthenium-catalyzed ring-closing metathesis (RCM) used to form the macrocyclic ring, and protects them against reduction during the hydrogenation of the resulting cycloalkene over Wilkinson's catalyst. As the C-silyl group can be concomitantly removed with the O-TBS substituent using tris(dimethylamino)sulfonium difluorotrimethylsilicate (TASF) in acetonitrile, no separate protecting group manipulations were necessary in the final stages, thus contributing to a favorable overall "economy of steps". In addition to the naturally occurring ipomoeassins, a small set of synthetic analogues has also been prepared by "diverted total synthesis". The cytotoxicity of these compounds was assayed with two different cancer cell lines. The recorded data confirm previous findings that the acylation- and oxygenation pattern of these amphiphilic glycoconjugates is highly correlated with their biological activity profile. Ipomoeassin F turned out to be the most promising member of the series, showing IC(50) values in the low nanomolar range.

Reusable catalysts for the asymmetric Diels-Alder reaction.

A new method for recycling chiral bis(oxazoline)-copper complexes is described based on the formation of charge-transfer complexes, their subsequent precipitation, and reuse after addition of new substrates. The conditions to perform this procedure were optimized in the presence of three bis(oxazoline)-based ligands. When associated with copper salts, these ligands efficiently catalyzed the Diels-Alder reaction between cyclopentadiene and alpha,beta-unsaturated acyloxazolidinones. These catalysts were successfully recycled up to ten times while maintaining their high activities and enantioselectivities.

A new method for recycling asymmetric catalysts via formation of charge transfer complexes.

[reaction: see text]. A new concept for recycling asymmetric bis(oxazoline)-type catalysts is reported. The formation of charge-transfer complexes between the chiral ligand and trinitrofluorenone and their subsequent precipitation and reuse by addition of new substrate solutions is described. The efficiency of this procedure is demonstrated in a Diels-Alder reaction to reach the expected endo product as major isomer (up to 97% de and 94% ee): the catalyst was used up to 12 times without loss of either activity or selectivity.