Greener solvents for the processing of preceramic polycarbosilane: application in the preparation of B4C/SiC composites.

The innovation introduced in this study consists of replacing toluene with safer solvents such as cyclopentane or diethyl ether in the processing of a preceramic polycarbosilane (allylhydridopolycarbosilane, AHPCS) and assessing its impact on the functionalisation of B4C powders to produce B4C/SiC composites. Fourier-transform infrared (FT-IR) with ATR and nuclear magnetic resonance (NMR) spectroscopy revealed no major modification in the polymer structure. SEC/MALS analysis showed a slight change in the number-average molar mass of the polymer regardless of the functionalisation solvent used in correlation with a slight decrease in the polymer ceramic yield due to oligomer loss. The thermal behaviour of the preceramic polymer investigated via mass spectrometry remained unaffected by the solvent change. The search for polymer residues after distillation highlighted the recyclability of both the functionalisation solvent and the polymer, despite a slight increase in the molar mass of the polymer. Finally, the sinterability of B4C/AHPCS samples was studied with the preparation of B4C/SiC composites via a polymer-derived ceramic (PDC) route and spark plasma sintering (SPS). The effect of the solvent on the microstructure and relative density of the specimens (>92%) is negligible. The specimens retain a fine and homogeneous phase distribution despite process modification. The results highlight the approach developed to use greener solvents for the chemical synthesis of functionalised ceramics and represent a step towards the generalisation of more environmentally friendly processes.

First Example of a Heptazine-Porphyrin Dyad; Synthesis and Spectroscopic Properties.

We have prepared the first example of a porphyrin linked to an heptazine photoactive antenna. The two entities, linked with an alkyl spacer, demonstrate the activity of both active moieties. While they behave electrochemically independantly, on the other hand the spectroscopy shows the existence of energy transfer between both partners.

Formation of ZrC-SiC Composites from the Molecular Scale through the Synthesis of Multielement Polymers.

In the field of non-oxide ceramic composites, and by using the polymer-derived ceramic route, understanding the relationship between the thermal behaviour of the preceramic polymers and their structure, leading to the mechanisms involved, is crucial. To investigate the role of Zr on the fabrication of ZrC-SiC composites, linear or hyperbranched polycarbosilanes and polyzirconocarbosilanes were synthesised through either "click-chemistry" or hydrosilylation reactions. Then, the thermal behaviours of these polymeric structures were considered, notably to understand the impact of Zr on the thermal path going to the composites. The inorganic materials were characterised by thermogravimetry-mass spectrometry (TG-MS), X-ray diffraction (XRD), and scanning electron microscopy (SEM). To link the macromolecular structure to the organisation involved during the ceramisation process, eight temperature domains were highlighted on the TG analyses, and a four-step mechanism was proposed for the polymers synthesised by a hydrosilylation reaction, as they displayed better ceramic yields. Globally, the introduction of Zr in the polymer had several effects on the temperature fragmentation mechanisms of the organometallic polymeric structures: (i) instead of stepwise mass losses, continuous fragment release prevailed; (ii) the stability of preceramic polymers was impacted, with relatively good ceramic yields; (iii) it modulated the chemical composition of the generated composites as it led, inter alia, to the consumption of free carbon.

Synthesis and biological evaluation of chalcone-polyamine conjugates as novel vectorized agents in colorectal and prostate cancer chemotherapy.

The aim of this study was to synthesize chalcone-polyamine conjugates in order to enhance bioavailability and selectivity of chalcone core towards cancer cells, using polyamine-based vectors. Indeed, it is well-known that polyamine transport system is upregulated in tumor cells. 3',4,4',5'-tetramethoxychalcone was selected as parent chalcone since it was found to be an efficient anti-proliferative agent on various cancer cells. A series of five chalcone-polyamine conjugates was obtained using the 4-bromopropyloxy-3',4',5'-trimethoxychalcone as a key intermediate. Chalcone core and polyamine tails were fused through an amine bond. These conjugates were found to possess a marked in vitro antiproliferative effect against colorectal (HT-29 and HCT-116) and prostate cancer (PC-3 and DU-145) cell lines. The most active conjugate (compound 8b) was then chosen for further biological evaluations to elucidate mechanisms responsible for its antiproliferative activity. Investigations on cell cycle distribution revealed that this conjugate can prevent the proliferation of human colorectal and prostate cancer cells by blocking the cell cycle at the G1 and G2 phase, respectively. Flow cytometry analysis revealed a sub-G1 peak, characteristic of apoptotic cell population and our inquiries highlighted apoptosis induction at early and later stages through several pro-apoptotic markers. Therefore, this chalcone-N1-spermidine conjugate could be considered as a promising agent for colon and prostatic cancer adjuvant therapy.

Chlorinated bianthrones from the cyanolichen Nephroma laevigatum.

While depsidones, depsides or dibenzofuran-like compounds dominate the chemical composition of lichens, the cyanolichen Nephroma laevigatum affords a diversity of quinoid pigments represented by chlorinated anthraquinones derived from emodin and new bianthrones resulting from the homo- or heterodimerization of monomers. Bianthrones were pointed out from the dichloromethane extract by MS/MS-based molecular networking, then isolated and characterized on the basis of extensive spectroscopic analyzes and GIAO NMR shift calculation followed by CP3 analyzes.

New Phenalenone Derivatives: Synthesis and Evaluation of Their Singlet Oxygen Quantum Yield.

1H-Phenalen-1-one is a very efficient and easy-to-synthesize photosensitizer. Many substitutions have been previously described, but most of them significantly reduce the singlet oxygen quantum yield. The chloromethyl derivative described elsewhere is a good starting point for the synthesis of many useful derivatives because of the methylene bridge that saves its unique photosensitizing properties. Eighteen new phenalenone derivatives have been synthesized, bearing amine, carboxylic acid, alcohol, azide, and other major functional groups in organic chemistry. These reactions were carried out in good-to-excellent yields, and most of these new compounds retained the singlet oxygen quantum yield of the parent molecule. These new derivatives are very promising precursors for a number of applications such as the development of photosensitive antimicrobial agents or materials.

Antibacterial activity of the lichens Usnea Florida and Flavoparmelia caperata (Parmeliaceae).

Acetone extracts of the two common epiphytes lichens Usnea florida and Flavoparmelia caperata have been evaluated for their antimicrobial activities against Staphylococcus aureus, Candida albicans and Aspergillus brasiliensis. The dibenzofuran derivative (+)-usnic acid (1) was the main metabolite in these two species. Thamnolic (5), evernic (6), physodic (7) and 3-hydroxyphysodic acids (8) were isolated from U. florida, as well as 5,7-dihydroxy-6-methylphtalide (2) which was newly identified in this Genus. Protocetraric (3) and caperatic acids (4) and ergosterol peroxide (9) are usually biosynthezised by F. caperata. Antibacterial activity was determined for the four main compounds against Staphylococcus aureus using bioautography and broth dilution method. Minimal inhibitory concentrations of usnic acid, caperatic acid and protocetraric acid were comprised between 7.25 and 12.5 µg/mL.

Enhancement of hydrosolubility and in vitro antiproliferative properties of chalcones following encapsulation into ß-cyclodextrin/cellulose-nanocrystal complexes.

This paper describes the preparation of two chalcone/ß-cyclodextrin/cellulose-nanocrystals complexes and the study of their antiproliferative activities against two colorectal and two prostatic cancer cell lines. The aim of this work was to enhance hydrosolubility of chalcones thanks to the hydrophilic character of cellulose nanocrystals. These latter were linked, through ionic interactions, to a cationic derivative of ß-cyclodextrins whose lipophilic cavity allowed the encapsulation of hydrophobic chalcones: 3-hydroxy-3',4,4',5'-tetramethoxychalcone (1) and 3',4,4',5'-tetramethoxychalcone (2). First, we showed that encapsulation allowed hydrosolubilization of chalcones. Then, chalcone/ß-cyclodextrin/cellulose-nanocrystals complexes demonstrated enhanced in vitro antiproliferative activities, compared to the corresponding free-chalcones.

Lysine Analogue of Polymyxin B as a Significant Opportunity for Photodynamic Antimicrobial Chemotherapy.

In order to highlight the potential of photodynamic antimicrobial chemotherapy in case of infections by antibiotic resistant-strains, a new antimicrobial peptide conjugate has been synthesized, consisting of a derivative of polymyxin B and a cationic porphyrin covalently attached together to a spacer. A polymyxin-derived moiety was subjected to a primary structural modification in the replacement of four diaminobutyrate residues with lysine ones. This modification was done in order to strongly reduce bactericidal activity, with the aim to eliminate the potential rise of polymyxin-resistant strains. Despite this modification, this new conjugate displayed a strong photobactericidal activity against Gram-positive as well as Gram-negative bacteria. It was further shown that this conjugate was able to strongly stick to the cell walls of either kind of strain, thus helping to inactivate bacteria through the production of reactive oxygen species under light irradiation.

Design and multi-step synthesis of chalcone-polyamine conjugates as potent antiproliferative agents.

The aim of this study is to synthesize chalcone-polyamine conjugates in order to enhance bioavailability and selectivity of chalcone core towards cancer cells, using polyamine-based vectors. 3-hydroxy-3',4,4',5'-tetramethoxychalcone (1) and 3',4,4',5'-tetramethoxychalcone (2) were selected as parent chalcones since they were found to be efficient anti-proliferative agents on various cancer cells. A series of ten chalcone-polyamine conjugates was obtained by reacting carboxychalcones with different polyamine tails. Chalcones 1 and 2 showed a strong cytotoxic activity against two prostatic cancer (PC-3 and DU-145) and two colorectal cancer (HT-29 and HCT-116) cell lines. Then, chalcone-spermine conjugates 7d and 8d were shown to be the most active of the series and could be considered as promising compounds for colon and prostatic cancer adjuvant therapy.

Cytochalasin E in the lichen Pleurosticta acetabulum. Anti-proliferative activity against human HT-29 colorectal cancer cells and quantitative variability.

A biological screening of sixteen lichen extracts on human HT-29 colorectal cancer cells, led to the selection of Pleurosticta acetabulum, a lichen widely present in tree barks in Europe. Bioguided purification of the acetonic extract resulted in the isolation of cytochalasin E, a common fungal metabolite. This compound is responsible for the anti-proliferative activity of the extract. Its presence in lichens is reported here for the first time. LC-MS quantitation of cytochalasin E in different samples of P. acetabulum demonstrated quantitative variations of cytochalasin E production in the lichen and especially high concentrations in apothecia.

Synthesis and Biological Evaluations of Click-Generated Nitrogen Mustards.

This paper describes the synthesis of new click-generated nitrogen mustards and their biological evaluation. By using the copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction, we managed to synthesize eight new nitrogen mustards. This strategy paves the way for the synthesis of a new family of nitrogen mustard, with an important structural variability. Furthermore, we studied the biological activity of synthesized compounds by testing their cytotoxicity on four representative cancer cell lines A431, JURKAT, K562, and U266. One structure, 1-benzyl-4-(N,N-di-2-chloroethylaminomethyl)-1H-[1,2,3]triazole, showed an interesting cytotoxic effect.

Uncommon chlorinated xanthone and other antibacterial compounds from the lichen Cladonia incrassata.

Bioassay-guided fractionation of an extract of the lichen Cladonia incrassata against Staphylococcus aureus led to a novel compound, 1,5-dihydroxy-2,4,6-trichloro-7-methylxanthone (1), along with six known compounds: (-)-usnic acid (2), didymic acid (3), condidymic acid (4), squamatic acid (5), thamnolic acid (6), and prasinic acid (7). Didymic, condidymic, and prasinic acids were isolated for the first time from C. incrassata. Didymic, condidymic, and (-)-usnic acids were active against S. aureus (a minimum inhibitory concentration of 7.5 µg/mL).

Reactivity of chalcones with 1-hydroxymethyl radicals.

Reactivity of chalcones with reactive species issued from methanol radiolysis was investigated in the absence or presence of dioxygen. Chalcones are natural antioxidants that are present in fruit and vegetables. Their degradation in the radiolysed solutions was followed by HPLC, NMR, FAB-LSIMS mass spectroscopy and analytical TLC in deaerated solution. Among the 18 identified radiolytic compounds, 16 were new. The formation of the radiolytic products was not influenced by A- and B-ring substitutions. To explain the degradation process, we thus suggested that the primary step was an attack of the alpha,beta-double bond by the 1-hydroxymethyl radical, either at C(alpha) or at C(beta). This step was followed by addition, cyclization or bond dissociations. Different chemical pathways were discussed that implicate the reactive species issued from methanol radiolysis. This paper highlights the relative importance of the different radical species, especially the carbon-centered radical, 1-hydroxymethyl (HMR) and the corresponding oxygen-centered isomer. In addition, an interesting unusual role of dioxygen should be noted; indeed, in the presence of dioxygen, degradation of chalcones was inhibited.

Radiolytic transformation of 2,2',4'-trihydroxychalcone.

Radiolysis of 2,2',4'-trihydroxychalcone, a natural antioxidant present in fruit and vegetables, was performed in ethanol in the absence or in the presence of dioxygen. The degradation process of chalcone was followed in de-aerated solution by HPLC, NMR, FAB-LSIMS mass spectroscopy and analytical TLC. Under anaerobic conditions, six new products (three couples of diastereoisomers) were identified. Four of them kept the chalcone skeleton with OCH(2)CH(3), CH(OH)CH(3) and H substitutions on C(alpha) and C(beta). Thus the target was the alpha-beta double bond on which ethanol radicals were added. The two other compounds were formed in a second stage and exhibited a cyclization between the substituent on C(beta) and the carbonyl group. In the presence of dioxygen, these reactions were prevented and chalcone was protected. This study was the first step toward understanding of the behavior chalcone in irradiated fruits and vegetables.

Synthesis and photocytotoxic activity of new chlorin-polyamine conjugates.

This paper reports the synthesis of new chlorin-polyamine conjugates designed to improve the targeting of cancer cells. Photocytotoxic activity of these photosensitizers was tested against human chronic myelogenous leukemia cells (K562) and compared to the effects of Photofrin II and chlorin e6.

New acyclonucleosides: synthesis and anti-HIV activity.

The synthesis of new acyclic nucleosides is described. These syntheses were accomplished by various methods: glycosylation, selective or total deprotection, oxidation/reduction, chlorination or azidation of hydroxyl groups. The compounds were characterized with NMR, mass and IR spectroscopy. Antiviral properties of these compounds were evaluated on HIV-1 infected cell lines.

Synthesis and evaluation of 4-triazolylflavans as new aromatase inhibitors.

Aromatase is a target of pharmacological interest for the treatment of estrogen-dependent cancers. Azole derivatives such as letrozole or anastrozole have been developed for aromatase inhibition and are used for the treatment of breast tumors. In this paper, four 4-triazolylflavans were synthesized and were found to exhibit moderate to high inhibitory activity against aromatase.

Synthesis and properties of new bolaform and macrocyclic galactose-based surfactants obtained by olefin metathesis.

A series of galactose-based surfactants with various structures likely to display new interesting properties were synthesized. Four monocatenary surfactants were elaborated by microwave-assisted galactosylation of undecanol or 10-undecenol. These compounds were slightly soluble in water. Their tensioactive properties were determined at 45 degrees C. Olefin metathesis was used to synthesize the two single-chain bolaforms from undec-10-enyl galactopyranosides; two pseudomacrocyclic bolaforms were prepared by grafting two carbamates at O-4 and O-4' sugar positions of the single-chain bolaforms. These four surfactants are insoluble in water and undergo monolayer compression. Cyclization of these bolaforms by olefin metathesis led to macrocyclic surfactant analogues of archaeobacterial membrane components.

Radiolysis of kaempferol in water/methanol mixtures. Evaluation of antioxidant activity of kaempferol and products formed.

Oxidative reaction between hydroxymethyl radical ((*)CH(2)OH) and kaempferol, in methanol and methanol/water mixtures, was studied by gamma-radiolysis using a (60)Co source. Radiolysis was performed with concentrations and doses ranging from 5 x 10(-)(5) M to 5 x 10(-)(3) M and from 0.5 kGy to 14 kGy, respectively. Kaempferol degradation was followed by HPLC. Results showed that (*)CH(2)OH reacts with kaempferol at the 3-OH group and produces two depsides (K1 and K2) and other products including K3. K1, K2, and K3 were identified by NMR, LC-MS, and HRMS. The kaempferol degradation pathway leading to the K1, K2, and K3 formation is proposed. It was observed that the more water concentration in the irradiation medium increases, the more K2 concentration increases. Comprehension of food preservation is not clear because many phenomena occurring during irradiation are not established. Radiolysis of kaempferol in water/methanol mixtures helps to elucidate the phenomenon and it is possible that during the treatment of nutriments by gamma-irradiation, a series of products such as depside K2 could be formed. Antioxidant properties of kaempferol radiolysis products were evaluated according to their capacity to decrease the EPR DPPH (1,1-diphenyl-2-picrylhydrazil) signal and to inhibit superoxide radicals formed by the enzyme reaction "xanthine + xanthine oxidase".