Synthesis of 7-hydroxydibenzopyran-6-ones via benzannulation of coumarins

We have successfully demonstrated a facile synthesis of a variety of 7-hydroxydibenzopyran-6-ones via a two-step protocol from 3-acylcoumarins having a latent Nazarov dienone functionality. Condensation of 3-acylcoumarins and ethyl cyanoacetate under basic (wet K₂CO₃) and microwave irradiation conditions followed by decarboethoxylative aromatization with Br₂ or DDQ furnished dibenzopyran-6-ones in high yields. The formation of ring C of the dibenzopyran-6-one motif critically depended on an active methylene compound and C7 substitution on coumarins. The Ar-Br or ArOTf substitution in dibenzopyran-6-ones was leveraged for the palladium-catalysed Suzuki coupling with diverse aryl boronic acids to increase the structural diversity. Reductive decyanation of C10 cyano dibenzopyran-6-ones furnished some of the isomers of urolithin A.

Podogigants A and B, two new potentiators of amphotericin B activity, from Sordariomycete Podostroma giganteum

Two new compounds, podogigants A (1) and B (2), were isolated from the culture broth of Podostroma giganteum. This is the first report on the identification of secondary metabolites in P. giganteum. The structures of 1 and 2 were elucidated through spectroscopic analysis, including 2D NMR spectroscopy assisted by chemical derivatization, which revealed the presence of farnesyl- and geranyl-hydroquinone structures, respectively. Compounds 1 and 2 exhibited no antifungal activity even at a concentration of 64 μg/mL, whereas they potentiated amphotericin B (AmB) activity against several species of fungi. In particular, 1 potentiated AmB activity against C. albicans and R. oryzae by up to 32-fold (MIC value of AmB decreased from 1.0 to 0.032 µg/mL), while 2 potentiated AmB activity against C. albicans by up to 16-fold.

Protein-functionalized nanoparticles derived from end-functional polymers and polymer prodrugs for crossing the blood-brain barrier

Nanoparticles may provide a viable way for neuroprotective drugs to cross the blood-brain barrier (BBB), which limits the passage of most drugs from the peripheral circulation to the brain. Heterotelechelic polymer prodrugs comprising a neuroprotective model drug (adenosine) and a maleimide functionality were synthesized by the "drug-initiated" approach and subsequent nitroxide exchange reaction. Nanoparticles were obtained by nanoprecipitation and exhibited high colloidal stability with diameters in the 162-185 nm range and narrow size distributions. Nanoparticles were then covalently surface-conjugated to different proteins (albumin, α2-macroglobulin and fetuin A) to test their capability of enhancing BBB translocation. Their performances in terms of endothelial permeability and cellular uptake in an in vitro BBB model were compared to that of similar nanoparticles with surface-adsorbed proteins, functionalized or not with the drug. It was shown that bare NPs (i.e., NPs not surface-functionalized with proteins) without the drug exhibited significant permeability and cellular uptake, which were further enhanced by NP surface functionalization with α2-macroglobulin. However, the presence of the drug at the polymer chain-end prevented efficient passage of all types of NPs through the BBB model, likely due to adecrease in the hydrophobicity of the nanoparticle surface and alteration of the protein binding/coupling, respectively. These results established a new and facile synthetic approach for the surface-functionalization of polymer nanoparticles for brain delivery purposes.

Nitroxide supported on nanometric metal oxides as new hybrid catalysts for selective sugar oxidation

A new series of supported organocatalysts, prepared by a simple method, were used for selective sugar oxidation. This approach is based on the immobilization of a nitroxide derivative through a carboxylic function on nanometric metal oxides (TiO₂, Al₂O₃ and CeO₂), allowing the recovery of the catalyst. These hybrid materials were carefully characterized by Diffuse Reflectance FT-IR spectroscopy (DRIFT), ThermoGravimetric Analysis (TGA), X-Ray Diffraction (XRD), Brunauer-Emmet-Teller surface area measurements (B.E.T.), elemental and electrochemical analyses, showing different characteristics and behaviors depending on the nature of the metal oxide used. The activity of the supported nitroxide catalyst was evaluated on methyl α-d-glucoside oxidation, used as model reaction. In all cases, high catalytic activity was highlighted, with up to 25 times less nitroxyl radical required for complete conversion than under homogeneous conditions. The influence of several experimental conditions such as the use of phosphate buffer and recyclability of the catalyst were also investigated.

Surface modification using TEMPO and its derivatives

This article provides an overview of the methods for surface modification based on the use of stable radicals: 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and its derivatives. Two approaches are discussed. The first relies on the immobilization of TEMPO moieties on the surface of various materials including silicon wafers, silica particles, organic polymers as well as diverse nanomaterials. Applications of such materials with spin labeled surface/interface, in (electro)catalysis, synthesis of novel hybrid nanostructures and nanocomposites as well as in designing of organic magnets and novel energy storage devices are also included in the discussion. The second approach utilizes TEMPO and its derivatives for the grafting of polymer chains and polymer brushes formation on flat and nanostructure surfaces via Nitroxide Mediated Radical Polymerization (NMRP). The influence of such polymer modification on surface/interface physicochemical properties is also presented.

An advanced and novel one-pot synthetic method for diverse benzo[c]chromen-6-ones by transition-metal free mild base-promoted domino reactions of substituted 2-hydroxychalcones with β-ketoesters and its application to polysubstituted terphenyls

Novel one-pot syntheses of a variety of benzo[c]chromen-6-one derivatives were accomplished by Cs₂CO₃-promoted reactions of 2-hydroxychalcones.

Verrulactones A and B, new inhibitors of Staphylococcus aureus enoyl-ACP reductase produced by Penicillium verruculosum F375

New dimeric compounds of alternariol class, verrulactones A and B, were isolated from a culture broth of the fungal strain Penicillium verruculosum F375 and their structure were established by various spectral analysis. Verrulactones A and B strongly inhibited Staphylococcus aureus enoyl-ACP reductase with IC(50) of 0.92 and 1.41 μM, respectively, and also showed antibacterial activity against S. aureus and MRSA with MICs of 8 and 16 μg/mL, respectively.