Mechanochemistry and Eco-Bases for Sustainable Michael Addition Reactions.

The Michael addition reaction was revisited with a full focus on sustainability combined with efficiency, using mechanochemistry in mild conditions. First, the synthesis of cyclopentenone derivatives was chosen as a model reaction to find optimal conditions in mechanochemistry while using classical but weak bases. The reaction was efficient (84-95% yields), fast (2-6 h), solvent free, and required 0.1 equivalent of base. Aiming to reach greener conditions, classical bases were then replaced using new bio-sourced bases, called Eco-bases, that were easily prepared from plants and led to heterogeneous catalysts. The composition and structure of Eco-bases were characterized by MP-AES, XRPD, EBSD/EDS, HRTEM/EDX and ion chromatography. Interestingly, a high ratio of potassium was observed with the presence of K2Ca(CO3)2 for the most effective Eco-base. The new Eco-bases were used for the mechanical-assisted construction of functionalized alkenone derivatives. The versatility of the method has been successfully applied with good to excellent yields to different Michael donors and acceptors. Eco-bases were recycled and reused four times with the same performances. Combining Eco-bases and mechanochemistry in Michael addition reactions allowed reaching a maximum degree of sustainability (efficient, rapid, low catalyst loading, solvent-free reactions with bio-sourced catalysts) and participating in the development of mechanochemistry in sustainable chemistry.

Structural basis for two efficient modes of agropinic acid opine import into the bacterial pathogen Agrobacterium tumefaciens.

Agrobacterium tumefaciens pathogens genetically modify their host plants to drive the synthesis of opines in plant tumors. The mannityl-opine family encompasses mannopine, mannopinic acid, agropine and agropinic acid. These opines serve as nutrients and are imported into bacteria via periplasmic-binding proteins (PBPs) in association with ABC transporters. Structural and affinity data on agropine and agropinic acid opines bound to PBPs are currently lacking. Here, we investigated the molecular basis of AgtB and AgaA, proposed as the specific PBP for agropine and agropinic acid import, respectively. Using genetic approaches and affinity measurements, we identified AgtB and its transporter as responsible for agropine uptake in agropine-assimilating agrobacteria. Nonetheless, we showed that AgtB binds agropinic acid with a higher affinity than agropine, and we structurally characterized the agropinic acid-binding mode through three crystal structures at 1.4, 1.74 and 1.9 Šresolution. In the crystallization time course, obtaining a crystal structure of AgtB with agropine was unsuccessful due to the spontaneous lactamization of agropine into agropinic acid. AgaA binds agropinic acid only with a similar affinity in nanomolar range as AgtB. The structure of AgaA bound to agropinic acid at 1.65 Šresolution defines a different agropinic acid-binding signature. Our work highlights the structural and functional characteristics of two efficient agropinic acid assimilation pathways, of which one is also involved in agropine assimilation.

Transcriptome analysis revealed that a quorum sensing system regulates the transfer of the pAt megaplasmid in Agrobacterium tumefaciens.

BACKGROUND: Agrobacterium tumefaciens strain P4 is atypical, as the strain is not pathogenic and produces a for this species unusual quorum sensing signal, identified as N-(3-hydroxy-octanoyl)-homoserine lactone (3OH,C8-HSL). RESULTS: By sequence analysis and cloning, a functional luxI-like gene, named cinI, has been identified on the At plasmid of A. tumefaciens strain P4. Insertion mutagenesis in the cinI gene and transcriptome analyses permitted the identification of 32 cinI-regulated genes in this strain, most of them encoding proteins responsible for the conjugative transfer of pAtP4. Among these genes were the avhB genes that encode a type 4 secretion system (T4SS) involved in the formation of the conjugation apparatus, the tra genes that encode the DNA transfer and replication (Dtr) machinery and cinI and two luxR orthologs. These last two genes, cinR and cinX, exhibit an unusual organization, with the cinI gene surrounded by the two luxR orthologs. Conjugation experiments confirmed that the conjugative transfer of pAtP4 is regulated by 3OH,C8-HSL. Root colonization experiments indicated that the quorum sensing regulation of the conjugation of the pAtP4 does not confer a gain or a loss of fitness to the bacterial host in the tomato plant rhizosphere. CONCLUSION: This work is the first identification of the occurrence of a quorum sensing regulation of the pAt conjugation phenomenon in Agrobacterium.

Evaluation of synthase and hemisynthase activities of glucosamine-6-phosphate synthase by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

Glucosamine-6-phosphate synthase (GlmS, EC 2.6.1.16) catalyzes the first and rate-limiting step in the hexosamine biosynthetic pathway, leading to the synthesis of uridine-5'-diphospho-N-acetyl-D-glucosamine, the major building block for the edification of peptidoglycan in bacteria, chitin in fungi, and glycoproteins in mammals. This bisubstrate enzyme converts D-fructose-6-phosphate (Fru-6P) and L-glutamine (Gln) into D-glucosamine-6-phosphate (GlcN-6P) and L-glutamate (Glu), respectively. We previously demonstrated that matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) allows determination of the kinetic parameters of the synthase activity. We propose here to refine the experimental protocol to quantify Glu and GlcN-6P, allowing determination of both hemisynthase and synthase parameters from a single assay kinetic experiment, while avoiding interferences encountered in other assays. It is the first time that MALDI-MS is used to survey the activity of a bisubstrate enzyme.

Efficient removal of persistent and emerging organic pollutants by biosorption using abundant biomass wastes.

Persistent and emerging organic pollutants represent a serious and global threat to human health and ecosystems. We describe here a simple, efficient and affordable technology for removing such organic pollutants from aquatic systems. Biosorption process was chosen, meeting these three criteria, and so that biosorbents should be biomass wastes combining the following characteristics: natural, cheap and abundant. Powdered dead roots from invasive alien species (Eichhornia crassipes, Pistia stratiotes and Fallopia japonica), and wastes rich in tannins such as coffee grounds and green tea grounds were tested as biosorbents for removing extensively used organic pollutants: organic UV-filters, insecticides and herbicides. The elemental composition and morphology of the biosorbents were fully determined. The biosorption kinetics for each pair of biosorbent/pollutant was described by a pseudo-second order model. Excellent biosorption efficiency was obtained for 10 µM solution of oxybenzone (89 ± 1%), octocrylene (90 ± 2%), lindane (88 ± 0%) and diuron (90 ± 1%) in only 2 h. And total removal of 10 µM of chlordecone (100 ± 0%) could be achieved, which could be of high concern for the population living in chlordecone-contaminated areas. As such pollutants can be found in aquatic ecosystems, an interference study with salts showed that biosorption efficiency remained as efficient in reconstituted seawater. A principal component analysis was performed as an attempt to rationalise the biosorption results. The solubility of the organic pollutants in water and the concentration of tanins in the biosorbents were key parameters.

Coupling the Torpedo microplate-receptor binding assay with mass spectrometry to detect cyclic imine neurotoxins.

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-α-bungarotoxin as tracer. Cyclic imine neurotoxins competitively inhibit biotinylated-α-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 address 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 matrixes with high sensitivity and reproducibility.

New biomaterials for Ni biosorption turned into catalysts for Suzuki-Miyaura cross coupling of aryl iodides in green conditions.

In parallel with increasing Ni production and utilisation, Ni pollution in the soil-water continuum has become an alarming and global problem. Solutions for removing Ni from industrial effluents have been widely investigated and biosorption has emerged as an efficient, cost-effective, scalable and sustainable alternative for water treatment. However, the biosorption capacity is limited by the chemical composition of the biomaterial and the Ni-enriched biomaterials are rarely valorised. In this work, the biosorption capacity of three abundant biomaterials with different chemical properties - water hyacinth, coffee grounds and pinecones - was studied before and after functionalization, and reached a maximum biosorption capacity of 51 mg g-1 of Ni(ii). A bioinspired functionalization approach was investigated introducing carboxylate moieties and was conducted in green conditions. The Ni-enriched biomaterials were valorised by transformation into catalysts, which were characterised by MP-AES and XRPD. Their characterisation revealed a structure similar to nickel formate, and hence the Eco-Ni(HCOO)2 catalysts were tested in Suzuki-Miyaura reactions. Several aryl iodides were successfully cross-coupled to phenylboronic acids using Eco-Ni(HCOO)2 without any ligand, a mild and green base in a mixture of green solvents.

Manganese distribution in the Mn-hyperaccumulator Grevillea meisneri from New Caledonia.

New Caledonian endemic Mn-hyperaccumulator Grevillea meisneri is useful species for the preparation of ecocatalysts, which contain Mn-Ca oxides that are very difficult to synthesize under laboratory conditions. Mechanisms leading to their formation in the ecocatalysts are unknown. Comparing tissue-level microdistribution of these two elements could provide clues. We studied tissue-level distribution of Mn, Ca, and other elements in different tissues of G. meisneri using micro-X-Ray Fluorescence-spectroscopy (µXRF), and the speciation of Mn by micro-X-ray Absorption Near Edge Structure (µXANES), comparing nursery-grown plants transplanted into the site, and similar-sized plants growing naturally on the site. Mirroring patterns in other Grevillea species, Mn concentrations were highest in leaf epidermal tissues, in cortex and vascular tissues of stems and primary roots, and in phloem and pericycle-endodermis of parent cluster roots. Strong positive Mn/Ca correlations were observed in every tissue of G. meisneri where Mn was the most concentrated. Mn foliar speciation confirmed what was already reported for G. exul, with strong evidence for carboxylate counter-ions. The co-localization of Ca and Mn in the same tissues of G. meisneri might in some way facilitate the formation of mixed Ca-Mn oxides upon preparation of Eco-CaMnOx ecocatalysts from this plant. Grevillea meisneri has been successfully used in rehabilitation of degraded mining sites in New Caledonia, and in supplying biomass for production of ecocatalysts. We showed that transplanted nursery-grown seedlings accumulate as much Mn as do spontaneous plants, and sequester Mn in the same tissues, demonstrating the feasibility of large-scale transplantation programs for generating Mn-rich biomass.

Contalactone, a contaminant formed during chemical synthesis of the strigolactone reference GR24 is also a strigolactone mimic.

Strigolactone (SL) plant hormones control plant architecture and are key players in both symbiotic and parasitic interactions. GR24, a synthetic SL analog, is the worldwide reference compound used in all bioassays for investigating the role of SLs in plant development and in rhizospheric interactions. In 2012, the first characterization of the SL receptor reported the detection of an unknown compound after incubation of GR24 samples with the SL receptor. We reveal here the origin of this compound (P270), which comes from a by-product formed during GR24 chemical synthesis. We present the identification of this by-product, named contalactone. A proposed chemical pathway for its formation is provided as well as an evaluation of its bioactivity on pea, Arabidopsis, root parasitic plant seeds and AM fungi, characterizing it as a SL mimic. Quality of GR24 samples can be easily checked by carrying out microscale hydrolysis in a basic aqueous medium to easily detect P270 as indicator of the presence of the contalactone impurity. In all cases, before being used for bioassays, GR24 must be careful purified by preparative HPLC.

Gymnemic acids inhibit hyphal growth and virulence in Candida albicans.

Candida albicans is an opportunistic and polymorphic fungal pathogen that causes mucosal, disseminated and invasive infections in humans. Transition from the yeast form to the hyphal form is one of the key virulence factors in C. albicans contributing to macrophage evasion, tissue invasion and biofilm formation. Nontoxic small molecules that inhibit C. albicans yeast-to-hypha conversion and hyphal growth could represent a valuable source for understanding pathogenic fungal morphogenesis, identifying drug targets and serving as templates for the development of novel antifungal agents. Here, we have identified the triterpenoid saponin family of gymnemic acids (GAs) as inhibitor of C. albicans morphogenesis. GAs were isolated and purified from Gymnema sylvestre leaves, the Ayurvedic traditional medicinal plant used to treat diabetes. Purified GAs had no effect on the growth and viability of C. albicans yeast cells but inhibited its yeast-to-hypha conversion under several hypha-inducing conditions, including the presence of serum. Moreover, GAs promoted the conversion of C. albicans hyphae into yeast cells under hypha inducing conditions. They also inhibited conidial germination and hyphal growth of Aspergillus sp. Finally, GAs inhibited the formation of invasive hyphae from C. albicans-infected Caenorhabditis elegans worms and rescued them from killing by C. albicans. Hence, GAs could be useful for various antifungal applications due to their traditional use in herbal medicine.

Bis-14-membered ring diketal diamines: synthesis and evaluation of their anti-HIV and anti-tumoral activities.

Chiral and achiral macrocyclic bis-diketal diamines, analogs of bicyclam AMD 3100, were synthesized in three steps from the previously obtained 14-membered ring diketal dilactams. Their monoreduction with lithium aluminium hydride gave the corresponding diketal aminolactams. Coupling these with dibromo-p-xylene led to xylyl dimer compounds. A second reduction step yielded the expected bis-diketal diamines in the methyl and unsubstituted series. Biological tests on the unreduced and reduced dimers showed both weak anti-HIV and anti-proliferative activities for the bis-diphenyl diketal aminolactam 13b, with a mode of action probably different from that of AMD 3100.

Robot-based tele-echography: clinical evaluation of the TER system in abdominal aortic exploration.

OBJECTIVE: The TER system is a robot-based tele-echography system allowing remote ultrasound examination. The specialist moves a mock-up of the ultrasound probe at the master site, and the robot reproduces the movements of the real probe, which sends back ultrasound images and force feedback. This tool could be used to perform ultrasound examinations in small health care centers or from isolated sites. The objective of this study was to prove, under real conditions, the feasibility and reliability of the TER system in detecting abdominal aortic and iliac aneurysms. METHODS: Fifty-eight patients were included in 2 centers in Brest and Grenoble, France. The remote examination was compared with the reference standard, the bedside examination, for aorta and iliac artery diameter measurement, detection and description of aneurysms, detection of atheromatosis, the duration of the examination, and acceptability. RESULTS: All aneurysms (8) were detected by both techniques as intramural thrombosis and extension to the iliac arteries. The interobserver correlation coefficient was 0.982 (P < .0001) for aortic diameters. The rate of concordance between 2 operators in evaluating atheromatosis was 84% +/- 11% (95% confidence interval). CONCLUSIONS: Our study on 58 patients suggests that the TER system could be a reliable, acceptable, and effective robot-based system for performing remote abdominal aortic ultrasound examinations. Research is continuing to improve the equipment for general abdominal use.