[show abstract][hide abstract] ABSTRACT: The ring-opening polymerization of beta-butyrolactone and lactide in solvent-free conditions and using NHC carboxylates as a (pre)catalyst is described. This class of catalysts enables the synthesis of aliphatic polyesters. These organocatalysts, which are easily synthesized, are remarkably robust, thus allowing the use of a bench-top reaction setup. In addition, NHC carboxylates are highly active in bulk conditions without the use of additives. Also, we have demonstrated for the first time that decarboxylation of NHC carboxylates depends on the nature of solvents under polymerization conditions.
[show abstract][hide abstract] ABSTRACT: New lupeol long-chain alkanoic ester 1 and lupeol β-hydroxy fatty acid esters 2c,d (laevigatins I and II) in a mixture with the previously isolated procrims a and b (2a,b) were isolated together with lupeol 3 and lupeol acetate 4 from the latex of Periploca laevigata collected in Tunisia. Their structures were elucidated by extensive spectroscopic methods including 1D (1H, 13C and DEPT 135), 2D-NMR experiments, (1H–1H COSY and NOESY), EI–MS, MALDI-TOF and GC analysis. Anti-acetylcholinesterase activity of most isolated compounds was evaluated and showed that lupeol (3) was the best inhibitor of AChE.
Arabian Journal of Chemistry 01/2013; · 2.27 Impact Factor
[show abstract][hide abstract] ABSTRACT: Cobalt and chromium complexes have been prepared from chiral calix–salen cyclic ligands. The corresponding tetrahydrosalen reduced forms have been used for copper salt complexation. These new chiral catalysts have been tested for their ability to promote asymmetric Henry reactions between various aldehydes and nitromethane under heterogeneous conditions. The best results were obtained by using tetrahydrosalen-based copper macrocycles, in terms of activity, selectivity, and stability during the recycling process. Ten consecutive runs could indeed be performed with the same catalyst batch to produce the target 1-(2-methoxy-phenyl)-2-nitro-ethanol with highly stable values in terms of yield and enantioselectivity (up to 94% ee).
[show abstract][hide abstract] ABSTRACT: Cyclic imine neurotoxins constitute an emergent family of neurotoxins of dinoflagellate origin that are potent antagonists of nicotinic acetylcholine receptors. We developed a target-directed functional method based on the mechanism of action of competitive agonists/antagonists of nicotinic acetylcholine receptors for the detection of marine cyclic imine neurotoxins. The key step for method development was the immobilization of Torpedo electrocyte membranes rich in nicotinic acetylcholine receptors on the surface of microplate wells and the use of biotinylated-a-bungarotoxin as tracer. Cyclic imine neurotoxins competitively inhibit biotinylated-a-bungarotoxin binding to Torpedo-nicotinic acetylcholine receptors in a concentration dependent manner. The microplate-receptor binding assay allowed rapid detection of nanomolar concentrations of cyclic imine neurotoxins directly in shellfish samples. Although highly sensitive and specific for the detection of neurotoxins targeting nicotinic acetylcholine receptors as a class, the receptor binding assay cannot identify a given analyte. To tackle the low selectivity of the microplate-receptor binding assay, the cyclic imine neurotoxins tightly bound to the coated Torpedo nicotinic receptor were eluted with methanol and the chemical nature of the eluted ligands was identified by mass spectrometry. The immobilization of Torpedo electrocyte membranes on the surface of microplate wells proved to be a high throughput format for the survey of neurotoxins targeting nicotinic acetylcholine receptors directly in shellfish matrices with high sensitivity and reproducibility.
[show abstract][hide abstract] ABSTRACT: The human tRNA m ( 5) C methyltransferase Misu is a novel downstream target of the proto-oncogene Myc that participates in controlling cell division and proliferation. Misu catalyzes the transfer of a methyl group from S-adenosyl-L-methionine to carbon 5 of cytosines in tRNAs. It was previously shown to catalyze in vitro the intron-dependent formation of m ( 5) C at the first position of the anticodon (position 34) within the human pre-tRNA (Leu) (CAA). In addition, it was recently reported that C48 and C49 are methylated in vivo by Misu. We report here the expression of hMisu in Escherichia coli and its purification to homogeneity. We show that this enzyme methylates position 48 in tRNA (Leu) (CAA) with or without intron and positions 48, 49 and 50 in tRNA (Gly2) (GCC) in vitro. Therefore, hMisu is the enzyme responsible for the methylation of at least four cytosines in human tRNAs. By comparison, the orthologous yeast enzyme Trm4 catalyzes the methylation of carbon 5 of cytosine at positions 34, 40, 48 or 49 depending on the tRNAs.
[show abstract][hide abstract] ABSTRACT: While ToF-SIMS is typically used to localize elemental ions in inorganic materials, it is also successfully utilized since several years to get images of a large variety of organic compounds, such as lipids (up to m/z 1500) at the surface of biological tissue sections. This technique can be associated with histology for medical diagnosis in order to correlate structural features with ion images. The possibility to use the same tissue section for both histology and mass spectrometry imaging would be a major advantage in terms of sample preparation and precision on the histological structure localization. In this study, on the one hand, rat brain sections were stained with Hematoxylin-Eosin (HE) after a ToF-SIMS surface analysis, and on the other hand, the lipid mapping with ToF-SIMS was performed after the HE staining procedure. In the first case, we evidenced that the high vacuum conditions applied in ToF-SIMS imaging did not disturb the staining neither the recognition of the brain structures. In the second case, a cholesterol fragment ion, chosen for imaging, was still detected in the brain structure after HE staining. However, it has not been possible to totally overlay the optical image before the staining with the ionic images after the staining, likely because of a distention of the tissue.
Surface and Interface Analysis 01/2012; 45(1):260-263. · 1.22 Impact Factor
[show abstract][hide abstract] ABSTRACT: We investigated in a rabbit model, the eye distribution of topically instilled benzalkonium_(BAK) chloride a commonly used preservative in eye drops using mass spectrometry imaging. Three groups of three New Zealand rabbits each were used: a control one without instillation, one receiving 0.01%BAK twice a day for 5 months and one with 0.2%BAK one drop a day for 1 month. After sacrifice, eyes were embedded and frozen in tragacanth gum. Serial cryosections were alternately deposited on glass slides for histological (hematoxylin-eosin staining) and immunohistological controls (CD45, RLA-DR and vimentin for inflammatory cell infiltration as well as vimentin for Müller glial cell activation) and ITO or stainless steel plates for MSI experiments using Matrix-assisted laser desorption ionization time-of-flight. The MSI results were confirmed by a round-robin study on several adjacent sections conducted in two different laboratories using different sample preparation methods, mass spectrometers and data analysis softwares. BAK was shown to penetrate healthy eyes even after a short duration and was not only detected on the ocular surface structures, but also in deeper tissues, especially in sensitive areas involved in glaucoma pathophysiology, such as the trabecular meshwork and the optic nerve areas, as confirmed by images with histological stainings. CD45-, RLA-DR- and vimentin-positive cells increased in treated eyes. Vimentin was found only in the inner layer of retina in normal eyes and increased in all retinal layers in treated eyes, confirming an activation response to a cell stress. This ocular toxicological study confirms the presence of BAK preservative in ocular surface structures as well as in deeper structures involved in glaucoma disease. The inflammatory cell infiltration and Müller glial cell activation confirmed the deleterious effect of BAK. Although these results were obtained in animals, they highlight the importance of the safety-first principle for the treatment of glaucoma patients.
PLoS ONE 01/2012; 7(11):e50180. · 3.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: An extract of Styrax agrestis fruits, collected in Vietnam, significantly inhibited acetylcholinesterase (AChE) in vitro. Bioassay-guided fractionation revealed three new egonol-type benzofurans: egonol-9(Z),12(Z) linoleate (1), 7-demethoxyegonol-9(Z),12(Z) linoleate (2), and 7-demethoxyegonol oleate (4). Ten known egonol-type benzofurans were also isolated (3, 5, 6-13). In order to better understand structure-activity relationships in this series, egonol derivatives 14-19 were prepared by chemical modifications and evaluated for their inhibition of AChE, butyrylcholinesterase (BChE), and AChE-induced Aβ aggregation. Compounds 1-4 were the most potent inhibitors of the series, which exhibited inhibitory activity against AChE (IC50 1.4-3.1 μM) and, for 1, Aβ aggregation (77.6%). Molecular docking studies were also performed to investigate interaction of these compounds with the active site of AChE.
Journal of Natural Products 09/2011; 74(10):2081-8. · 3.29 Impact Factor
[show abstract][hide abstract] ABSTRACT: The flavoprotein TrmFO catalyzes the C5 methylation of uridine 54 in the TΨC loop of tRNAs using 5,10-methylenetetrahydrofolate (CH(2)THF) as a methylene donor and FAD as a reducing agent. Here, we report biochemical and spectroscopic studies that unravel the remarkable capability of Bacillus subtilis TrmFO to stabilize, in the presence of oxygen, several flavin-reduced forms, including an FADH(•) radical, and a catalytic intermediate endowed with methylating activity. The FADH(•) radical was characterized by high-field electron paramagnetic resonance and electron nuclear double-resonance spectroscopies. Interestingly, the enzyme exhibited tRNA methylation activity in the absence of both an added carbon donor and an external reducing agent, indicating that a reaction intermediate, containing presumably CH(2)THF and FAD hydroquinone, is present in the freshly purified enzyme. Isolation by acid treatment, under anaerobic conditions, of noncovalently bound molecules, followed by mass spectrometry analysis, confirmed the presence in TrmFO of nonmodified FAD. Addition of formaldehyde to the purified enzyme protects the reduced flavins from decay by probably preventing degradation of CH(2)THF. The absence of air-stable reduced FAD species during anaerobic titration of oxidized TrmFO, performed in the absence or presence of added CH(2)THF, argues against their thermodynamic stabilization but rather implicates their kinetic trapping by the enzyme. Altogether, the unexpected isolation of a stable catalytic intermediate suggests that the flavin-binding pocket of TrmFO is a highly insulated environment, diverting the reduced FAD present in this intermediate from uncoupled reactions.
[show abstract][hide abstract] ABSTRACT: Guadeloupean Parkinsonism has been linked epidemiologically to the consumption of Annonaceae fruits. These were proposed to be etiological agents for sporadic atypical Parkinsonism worldwide, because of their content of neurotoxins such as isoquinolinic alkaloids and Annonaceous acetogenins. The pulp of Annona cherimolia Mill. from Spain was screened for these toxic molecules using Matrix-Assisted Laser Desorption Ionisation - Time of Flight mass spectrometry (MALDI-TOF MS) and it was found not to be a source of exposure. However, kaurenoic acid, a diterpene considered to be cytotoxic, was detected in high amounts (66 mg/fresh fruit). Treatment of rat embryonic striatal primary cultures, up to a high concentration (50 µM), did not cause neuronal death nor astrogliosis, suggesting that this molecule is not at risk of implication in human neurodegenerative diseases.
Phytotherapy Research 04/2011; 25(12):1861-4. · 2.07 Impact Factor
[show abstract][hide abstract] ABSTRACT: Mass spectrometry imaging of lipids using MALDI-TOF/TOF mass spectrometers is of growing interest for chemical mapping of organic compounds at the surface of tissue sections. Many efforts have been devoted to the best matrix choice and deposition technique. Nevertheless, the identification of lipid species desorbed from tissue sections remains problematic. It is now well-known that protonated, sodium- and potassium-cationized lipids are detected from biological samples, thus complicating the data analysis. A new sample preparation method is proposed, involving the use of lithium salts in the matrix solution in order to simplify the mass spectra with only lithium-cationized molecules instead of a mixture of various cationized species. Five different lithium salts were tested. Among them, lithium trifluoroacetate and lithium iodide merged the different lipid adducts into one single lithium-cationized species. An optimized sample preparation protocol demonstrated that the lithium trifluoroacetate salt slightly increased desorption of phosphatidylcholines. Mass spectrometry images acquired on rat brain tissue sections by adding lithium trifluoroacetate showed the best results in terms of image contrast. Moreover, more structurally relevant fragments were generated by tandem mass spectrometry when analyzing lithium-cationized species.
Analytical and Bioanalytical Chemistry 03/2011; 401(1):75-87. · 3.66 Impact Factor
[show abstract][hide abstract] ABSTRACT: Novel gold(I) complexes containing N-heterocyclic carbene ligands
have been synthesized and fully characterized. The resulting mononuclear gold
complexes act as active initiators in the polymerization of rac-β-butyrolactone under solvent-free conditions to provide the corresponding biodegradable poly(3-hydroxybutyrate).
[show abstract][hide abstract] ABSTRACT: A new acrylamide-type monomer (N-(4-hydroxy-3-methoxy-benzyl)-acrylamide) derived from guaiacol was successfully synthesized. Polymers containing guaiacol moiety were obtained via conventional radical polymerization of this monomer with AIBN as initiator. The influence of reaction time, initiator concentration and temperature on polymers characteristics was studied. Evaluation of the termination mode in free-radical polymerization was performed by MALDI-TOF mass spectrometry. Termination occurs mainly by disproportionation reaction. Additional peaks in the spectrum were attributed to side chain reactions implying phenoxy radicals. This new polymer exhibits a potential antibacterial activity against Bacillus subtilis by using anti-adhesion and anti-biofilm tests. After an adhesion time of 3 h, compared to a non-coated glass slide, there was a decrease of bacteria of 99% on the polymer coated glass slide. After three days of culture in a bacterial suspension, no biofilm was observed on the polymer coated surface.Graphical abstract
[show abstract][hide abstract] ABSTRACT: We describe here the conjugation of polyclonal goat anti-rabbit antibody to generation 4 polyamidoamine (G4-PAMAM) dendrimers carrying (i) (η(5)-cyclopentadienyl) iron dicarbonyl succinimidato complexes as infrared (IR) probes, (ii) nitroaniline entities as nuclear magnetic resonance (NMR) probes, (iii) acetamide groups for surface neutralization, and (iv) hydrazide-terminated spacer arms for the reaction with aldehyde. To preserve a high binding affinity, the conjugation was performed on the carbohydrate moieties located on the Fc fragment. The resulting conjugates were characterized by Fourier transform-IR, ultraviolet (UV), and high-mass matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. On the basis of relative concentration ratios of IR probes and antibody, an average labeling of 30 IR probes per antibody was reached (i.e., more than twice the value obtained with our previous strategy that generated no spacer arm). Immunoassays revealed that the antibody-dendrimer conjugates retained 55.1% of immunoreactivity on average with respect to underivatized antibody. Finally, the conjugates were used to quantify their antigen by solid-phase carbonyl metallo immunoassay (CMIA). Results showed a significant enhancement of the IR signal, demonstrating the efficiency of the new conjugation strategy and the potential of the new antibody-dendrimer conjugates as universal immunoanalytical reagents.
[show abstract][hide abstract] ABSTRACT: The S-adenosyl-L-methionine dependent methylation of adenine 58 in the T-loop of tRNAs is essential for cell growth in yeast or for adaptation to high temperatures in thermophilic organisms. In contrast to bacterial and eukaryotic tRNA m(1)A58 methyltransferases that are site-specific, the homologous archaeal enzyme from Pyrococcus abyssi catalyzes the formation of m(1)A also at the adjacent position 57, m(1)A57 being a precursor of 1-methylinosine. We report here the crystal structure of P. abyssi tRNA m(1)A57/58 methyltransferase ((Pab)TrmI), in complex with S-adenosyl-L-methionine or S-adenosyl-L-homocysteine in three different space groups. The fold of the monomer and the tetrameric architecture are similar to those of the bacterial enzymes. However, the inter-monomer contacts exhibit unique features. In particular, four disulfide bonds contribute to the hyperthermostability of the archaeal enzyme since their mutation lowers the melting temperature by 16.5°C. His78 in conserved motif X, which is present only in TrmIs from the Thermococcocales order, lies near the active site and displays two alternative conformations. Mutagenesis indicates His78 is important for catalytic efficiency of (Pab)TrmI. When A59 is absent in tRNA(Asp), only A57 is modified. Identification of the methylated positions in tRNAAsp by mass spectrometry confirms that (Pab)TrmI methylates the first adenine of an AA sequence.
Nucleic Acids Research 10/2010; 38(18):6206-18. · 8.28 Impact Factor