Investigation on the stoichiometry of carbon dioxide in isotope-exchange reactions with phenylacetic acids

International audienceThe functionalization of carbon dioxide (CO$_2$) as a C1 building block has attracted enormous attention. Carboxylation reactions, in particular, are of major interest for applications in isotope labeling. Due to the inexpensive nature of CO$_2$, information about its stoichiometric use is generally unavailable in the literature. Because of the rarity and limited availability of CO$_2$ isotopomers, this parameter is of concern for applications in carbon-isotope labeling. We investigated the effects of the stoichiometry of labeled CO$_2$ on carbon isotope exchange of phenyl­acetic acids. Both thermal and photocatalytic procedures were studied, providing insight into product outcome and isotope incorporation. Preliminary results on isotope-dilution effects of carbonate bases in photocatalytic carboxylation reactions have also been obtained

T Cell Immunity to the Alkyl Hydroperoxide Reductase of Burkholderia pseudomallei: A Correlate of Disease Outcome in Acute Melioidosis.

There is an urgent need for a better understanding of adaptive immunity to Burkholderia pseudomallei, the causative agent of melioidosis that is frequently associated with sepsis or death in patients in Southeast Asia and Northern Australia. The imperative to identify vaccine targets is driven both by the public health agenda in these regions and biological threat concerns. In several intracellular bacterial pathogens, alkyl hydroperoxidase reductases are upregulated as part of the response to host oxidative stress, and they can stimulate strong adaptive immunity. We show that alkyl hydroperoxidase reductase (AhpC) of B. pseudomallei is strongly immunogenic for T cells of 'humanized' HLA transgenic mice and seropositive human donors. Some T cell epitopes, such as p6, are able to bind diverse HLA class II heterodimers and stimulate strong T cell immunity in mice and humans. Importantly, patients with acute melioidosis who survive infection show stronger T cell responses to AhpC relative to those who do not. Although the sequence of AhpC is virtually invariant among global B. pseudomallei clinical isolates, a Cambodian isolate varies only in C-terminal truncation of the p6 T cell epitope, raising the possibility of selection by host immunity. This variant peptide is virtually unable to stimulate T cell immunity. For an infection in which there has been debate about centrality of T cell immunity in defense, these observations support a role for T cell immunity to AhpC in disease protection

Parallel Screening with 14 C‐Labeled Carbon Dioxide: De‐risking the Staudinger‐Aza‐Wittig Reaction**

International audienceAbstract Carbon isotope labeling is a useful technology for tracking the fate of organic compounds in the environment and in living organisms. In this context, the development of robust and general methodologies amenable to the direct functionalization of CO 2 remains a significant task. In this communication, a de‐risking approach was developed to evaluate the robustness of the Staudinger aza‐Wittig sequence for carbon isotope labeling. This technology is based on [ 14 C]CO 2 screening that allowed to investigate the tolerance of the procedure with most representative heterocycles and functional groups found in FDA approved drugs

Synthesis and studies on the mGluR agonist activity of FAP4 stereoisomers

International audienceThe four stereoisomers of 1-amino-2-fluoro-2-(phosphonomethyl)cyclopropane-1-carboxylic acid (FAP4) were synthesized via diastereoselective Rh(II)-catalysed cyclopropanation of a phosphonylated fluoroalkene. Different isomers of FAP4 and the corresponding non-fluorinated analogs showed a similar pharmacological profile against the isoforms of metabotropic glutamate receptor (mGluR). Within the fluorinated series, (-)-(Z)-FAP4 and (-)-(E)-FAP4 demonstrated the highest agonist activity against mGlu4 (EC50 0.10 microM). Our results suggest that fluorocyclopropanes bearing an amino-acid function can be suitable for the development of potent conformationally restricted mGluR agonists

The neurotoxic effect of 13, 19-didesmethyl and 13-desmethyl spirolide C phycotoxins is mainly mediated by nicotinic rather than muscarinic acetylcholine receptors.

International audienceSpirolides are a large family of lipophilic marine toxins produced by dinoflagellates that have been detected in contaminated shellfish. Among them, 13,19-didesmethyl and 13-desmethyl spirolide C phycotoxins are widely distributed and their mode of action needs to be clearly defined. In order to further characterize the pharmacological profiles of these phycotoxins on various nicotinic acetylcholine receptor (nAChR) subtypes and to examine whether they act on muscarinic receptors (mAChRs), functional electrophysiological studies and competition binding experiments have been performed. While 13-desmethyl spirolide C interacted efficiently with sub-nanomolar affinities and low selectivity with muscular and neuronal nAChRs, 13,19-didesmethyl spirolide C was more selective of muscular and homopentameric a7 receptors and recognized only weakly neuronal heteropentameric receptors, especially the a4b2 subtype. Thus, the presence of an additional methyl group on the tetrahydropyran ring significantly modified the pharmacological profile of 13-desmethyl spirolide C by notably increasing its affinity on certain neuronal nAChRs. Structural explanations of this selectivity difference are proposed, based on molecular docking experiments modeling different spirolide-receptor complexes. In addition, the 2 spirolides interacted only with low micromolar affinities with the 5 mAChRs, highlighting that the toxicity of the spirolide C analogs is mainly due to their high inhibition potency on various peripheral and central nAChRs and not to their low ability to interact with mAChR subtypes

Robust and General Procedure for Carbon Isotope Labeling of Linear Urea Derivatives with Carbon Dioxide

Carbon isotope labeling is a traceless technology, which allows tracking the fate of organic compounds either in the environment or in living organisms. Despite recent advances in the field, the development of robust and general technologies remains a significant task. This full article reports on a general approach to label urea derivatives with all carbon isotopes, including 14C and 11C. Based on a Staudinger aza-Wittig sequence, it provides access to all aliphatic/aromatic urea combinations as well as to semicarbazides, sulfonylureas, hydroxyl ureas, and simple terminal ureas. A de-risking approach was developed to evaluate the robustness of the reaction. This technology is based on [14C]CO2 screening that allowed to investigate the tolerance of the procedure with most representative heterocycles and functional groups found in FDA approved drugs

A general procedure for carbon isotope labeling of linear urea derivatives with carbon dioxide

International audienceCarbon isotope labeling is a traceless technology, which allows tracking the fate of organic compounds either in the environment or in living organisms. This article reports on a general approach to label urea derivatives with all carbon isotopes, including 14C and 11C, based on a Staudinger aza-Wittig sequence. It provides access to all aliphatic/aromatic urea combinations

The Translocation Domain of Botulinum Neurotoxin A Moderates the Propensity of the Catalytic Domain to Interact with Membranes at Acidic pH

International audienceBotulinum neurotoxin A (BoNT/A) is composed of three domains: a catalytic domain (LC), a translocation domain (H N) and a receptor-binding domain (H C). Like most bacterial toxins BoNT/A is an amphitropic protein, produced in a soluble form that is able to interact, penetrate and/or cross a membrane to achieve its toxic function. During intoxication BoNT/A is internalized by the cell by receptor-mediated endocytosis. Then, LC crosses the membrane of the endocytic compartment and reaches the cytosol. This translocation is initiated by the low pH found in this compartment. It has been suggested that LC passes in an unfolded state through a transmembrane passage formed by H N. We report here that acidification induces no major conformational change in either secondary or tertiary structures of LC and H N of BoNT/A in solution. GdnHCl-induced denaturation experiments showed that the stability of LC and H N increases as pH drops, and that H N further stabilizes LC. Unexpectedly we found that LC has a high propensity to interact with and permeabilize anionic lipid bilay-ers upon acidification without the help of H N. This property is downplayed when LC is linked to H N. H N thus acts as a chaperone for LC by enhancing its stability but also as a moderator of the membrane interaction of LC

Correction: The Translocation Domain of Botulinum Neurotoxin A Moderates the Propensity of the Catalytic Domain to Interact with Membranes at Acidic pH.

International audience[This corrects the article DOI: 10.1371/journal.pone.0153401.]