Search

International audience; Uncovering the basis of small molecule hormone receptors evolution is paramount to a complete understanding of how protein structure drives function. In plants, hormone receptors for strigolactones are well suited to evolutionary inquires because closely related homologs have different ligand preferences. More importantly, because of facile plant transgenic systems, receptors can be swapped and quickly assessed functionally in vivo. Here, we show only three mutations are required to switch the non-strigolactone receptor, KAI2, into a strigolactone receptor. This modified receptor still perceives KAI2 ligands and does not require receptor hydrolysis for activity. Structural and molecular dynamic modeling suggest receptor pocket flexibility is important for ligand specificity and downstream signaling partner affinity. These findings indicate a few keystone mutations link strigolactone signaling to germination, which explains how parasitic plants that devastate African agriculture evolved SL receptors to sense the presence of a host plant.

International audience; Phelipanche ramosa is an obligate root-parasitic weed that threatens major crops in central Europe. In order to germinate, it must perceive various structurally divergent host-exuded signals, including isothiocyanates (ITCs) and strigolactones (SLs). However, the receptors involved are still uncharacterized. Here, we identify five putative SL receptors in P. ramosa and show that PrKAI2d3 is involved in the stimulation of seed germination. We demonstrate the high plasticity of PrKAI2d3, which allows it to interact with different chemicals, including ITCs. The SL perception mechanism of PrKAI2d3 is similar to that of endogenous SLs in non-parasitic plants. We provide evidence that PrKAI2d3 enzymatic activity confers hypersensitivity to SLs. Additionally, we demonstrate that methylbutenolide-OH binds PrKAI2d3 and stimulates P. ramosa germination with bioactivity comparable to that of ITCs. This study demonstrates that P. ramosa has extended its signal perception system during evolution, a fact that should be considered for the development of specific and efficient biocontrol methods.

The F-box protein MORE AXILLARY GROWTH 2 (MAX2) is a central component in the signaling cascade of strigolactones (SLs) as well as of the smoke-derived karrikins (KARs) and the so far unknown endogenous KAI2 ligand (KL). The two groups of molecules are involved in overlapping and unique developmental processes, and signal-specific outcomes are attributed to perception by the paralogous α/β-hydrolases DWARF14 (D14) for SL and KARRIKIN INSENSITIVE 2/HYPOSENSITIVE TO LIGHT (KAI2/HTL) for KAR/KL. In addition, depending on which receptor is activated, specific members of the SUPPRESSOR OF MAX2 1 (SMAX1)-LIKE (SMXL) family control KAR/KL and SL responses. As proteins that function in the same signal transduction pathway often occur in large protein complexes, we aimed at discovering new players of the MAX2, D14, and KAI2 protein network by tandem affinity purification in Arabidopsis cell cultures. When using MAX2 as a bait, various proteins were copurified, among which were general components of the Skp1-Cullin-F-box complex and members of the CONSTITUTIVE PHOTOMORPHOGENIC 9 signalosome. Here, we report the identification of a novel interactor of MAX2, a type 5 serine/threonine protein phosphatase, designated PHYTOCHROME-ASSOCIATED PROTEIN PHOSPHATASE 5 (PAPP5). Quantitative affinity purification pointed at PAPP5 as being more present in KAI2 rather than in D14 protein complexes. In agreement, mutant analysis suggests that PAPP5 modulates KAR/KL-dependent seed germination under suboptimal conditions and seedling development. In addition, a phosphopeptide enrichment experiment revealed that PAPP5 might dephosphorylate MAX2 in vivo independently of the synthetic SL analog, rac-GR24. Together, by analyzing the protein complexes to which MAX2, D14, and KAI2 belong, we revealed a new MAX2 interactor, PAPP5, that might act through dephosphorylation of MAX2 to control mainly KAR/KL-related phenotypes and, hence, provide another link with the light pathway., Graphical Abstract, Highlights • TAP revealed PAPP5 as a novel interactor of MAX2. • PAPP5 might act through dephosphorylation of MAX2. • PAPP5 modulates KAI2-controlled responses in seeds and young seedlings. • PAPP5 might be another link between KAR/KL signaling and light., In Brief The F-box protein MAX2 is a central component in the signaling pathway of the phytohormones, strigolactones and smoke-derived karrikins. These molecules are perceived by the related receptors D14 and KAI2, respectively. Here, we used tandem and single affinity purifications to broaden the MAX2, KAI2, and D14 interaction network and identified PAPP5 as a novel player. PAPP5 might act via dephosphorylation of MAX2 to modulate KAI2-dependent seed germination and young seedling phenotypes.

In angiosperms, the α/β hydrolase DWARF14 (D14), along with the F-box protein MORE AXILLARY GROWTH2 (MAX2), perceives strigolactones (SL) to regulate developmental processes. The key SL biosynthetic enzyme CAROTENOID CLEAVAGE DIOXYGENASE8 (CCD8) is present in the moss Physcomitrium patens, and PpCCD8-derived compounds regulate moss extension. The PpMAX2 homolog is not involved in the SL response, but 13 PpKAI2LIKE (PpKAI2L) genes homologous to the D14 ancestral paralog KARRIKIN INSENSITIVE2 (KAI2) encode candidate SL receptors. In Arabidopsis thaliana, AtKAI2 perceives karrikins and the elusive endogenous KAI2-Ligand (KL). Here, germination assays of the parasitic plant Phelipanche ramosa suggested that PpCCD8-derived compounds are likely noncanonical SLs. (+)-GR24 SL analog is a good mimic for PpCCD8-derived compounds in P. patens, while the effects of its enantiomer (−)-GR24, a KL mimic in angiosperms, are minimal. Interaction and binding assays of seven PpKAI2L proteins pointed to the stereoselectivity toward (−)-GR24 for a single clade of PpKAI2L (eu-KAI2). Enzyme assays highlighted the peculiar behavior of PpKAI2L-H. Phenotypic characterization of Ppkai2l mutants showed that eu-KAI2 genes are not involved in the perception of PpCCD8-derived compounds but act in a PpMAX2-dependent pathway. In contrast, mutations in PpKAI2L-G, and -J genes abolished the response to the (+)-GR24 enantiomer, suggesting that PpKAI2L-G, and -J proteins are receptors for moss SLs.

In flowering plants, the α/β hydrolase DWARF14 (D14) perceives strigolactone (SL) hormones and interacts with the F-box protein MORE AXILLARY GROWTH2 (MAX2) to regulate developmental processes. The key SL biosynthetic enzyme, CAROTENOID CLEAVAGE DEOXYGENASE8 (CCD8), is present in the mossPhyscomitrium (Physcomitrella) patens,and PpCCD8-derived compounds regulate plant extension. Based on germination assays using seeds of the parasitic plantPhelipanche ramosa,we propose that these compounds are non-canonical SLs. Perception of PpCCD8-derived compounds does not require the PpMAX2 homolog. Candidate receptors are among the 13PpKAI2LIKE-A to -Lgenes, homologous to the ancestralD14paralogKARRIKIN INSENSITIVE2 (KAI2).In Arabidopsis, AtKAI2 is the receptor for a still elusive endogenous KAI2-Ligand (KL). We show that inP. patens,among SL analogs, the (+)-GR24 enantiomer is a good mimic for PpCCD8-derived compounds, while the effects of the (-)-GR24 enantiomer, a KL mimic in flowering plants, are opposite. Interaction and binding assays of seven PpKAI2L proteins using pure enantiomers pinpoint at stereoselectivity towards (-)-GR24 for the (A-E) clade. Enzyme assays highlight strong hydrolytic activity of the PpKAI2L-H protein. Moss mutants for allPpKAI2Lgene subclades were obtained and tested for their response to both enantiomers. We show thatPpKAI2L-Ato-Egenes are not involved in PpCCD8-derived compound perception, but act in a PpMAX2-dependant pathway. In contrast, mutations inPpKAI2L-G, and-Jgenes abolish the response to (+)-GR24, suggesting that encoded proteins are receptors for PpCCD8-derived SLs.

Karrikins (KARs), smoke-derived butenolides, are perceived by the α/β-fold hydrolase KARRIKIN INSENSITIVE2 (KAI2) and thought to mimic endogenous, yet elusive plant hormones tentatively called KAI2-ligands (KLs). The sensitivity to different karrikin types as well as the number of KAI2 paralogs varies among plant species, suggesting diversification and co-evolution of ligand-receptor relationships. We found that the genomes of legumes, comprising a number of important crops with protein-rich, nutritious seed, contain two or more KAI2 copies. We uncover sub-functionalization of the two KAI2 versions in the model legume Lotus japonicus and demonstrate differences in their ability to bind the synthetic ligand GR24ent-5DS in vitro and in genetic assays with Lotus japonicus and the heterologous Arabidopsis thaliana background. These differences can be explained by the exchange of a widely conserved phenylalanine in the binding pocket of KAI2a with a tryptophan in KAI2b, which arose independently in KAI2 proteins of several unrelated angiosperms. Furthermore, two polymorphic residues in the binding pocket are conserved across a number of legumes and may contribute to ligand binding preferences. The diversification of KAI2 binding pockets suggests the occurrence of several different KLs acting in non-fire following plants, or an escape from possible antagonistic exogenous molecules. Unexpectedly, L. japonicus responds to diverse synthetic KAI2-ligands in an organ-specific manner. Hypocotyl growth responds to KAR1, KAR2 and rac-GR24, while root system development responds only to KAR1. This differential responsiveness cannot be explained by receptor-ligand preferences alone, because LjKAI2a is sufficient for karrikin responses in the hypocotyl, while LjKAI2a and LjKAI2b operate redundantly in roots. Instead, it likely reflects differences between plant organs in their ability to transport or metabolise the synthetic KLs. Our findings provide new insights into the evolution and diversity of butenolide ligand-receptor relationships, and open novel research avenues into their ecological significance and the mechanisms controlling developmental responses to divergent KLs., Author summary Plant hormone signaling is crucial for development and for adequate responses to biotic and abiotic environmental conditions. The most recently discovered plant hormone receptor KARRIKIN INSENSITVE 2 (KAI2), binds a small butenolide called karrikin that was discovered in smoke and induces germination of fire-following plants. Several lines of evidence suggest a yet elusive endogenous hormone, which acts as ligand for KAI2. Until its identification, synthetic karrikins or the strigolactone-like molecule GR24 are used to probe the karrikin signaling pathway. While the model plant Arabidopsis contains only one KAI2 gene, several copies are maintained in other species suggesting sub-functionalization. We report that genomes of species in the legume hologalegina clade encode two KAI2 versions. In Lotus japonicus, they diverge in their binding ability to synthetic ligands due to three amino acid changes in their binding pocket, of which two are conserved across legumes and one has independently occurred in several species across the angiosperm phylogeny. Surprisingly, L. japonicus hypocotyls react with developmental responses to two different karrikins (KAR1, KAR2) and a synthetic strigolactone rac-GR24, while root development responds only to KAR1. This shows that there is not only diversity in ligand-receptor relationships but possibly also organ-specific uptake or metabolism of divergent butenolide molecules.

International audience

International audience; A novel class of reversible chiral ammonium‐based ionic liquids has been designed and synthesized. These chiral ammonium carbamate salts were quickly obtained by adding 1 atmosphere of CO2 gas to chiral silylated amines, easily prepared at gram scale and in some steps from natural amino acids as bio‐renewable substrates. Some physical properties of these reversible chiral ionic liquids such as reversibility temperature, thermal degradation, miscibility, and stability have been determined. The spectroscopic characteristics of the silylated amine and ionic liquid states have also been compared. The properties of reversibility, chirality, and ease of preparation should make these silylamine‐ionic liquid phases as promising solvents and/or catalysts for several applications, especially in asymmetric catalysis fields.

International audience; The activation of aryl glycosyl sulfone donors has been achieved using scandium(III) triflate and has led to the selective preparation of alpha-mannosides resulting from a post-glycosylation anomerization.

International audience; Lipo-chitotetrasaccharide analogues where one central GlcNAc residue was replaced by a triazole unit have been synthesized from a derivative obtained by chitin depolymerization and a functionalized N-acetyl-glucosamine via the copper-catalyzed azide-alkyne cycloaddition. Their evaluation in a binding assay using LYR3, a putative lipo-chitooligosaccharide receptor in Medicago truncatula, shows a complete loss of binding.

International audience; Strigolactone plant hormones control plant architecture and are key players in both symbiotic and parasitic interactions. They contain an ABC tricyclic lactone connected to a butenolide group, the D ring. The DWARF14 (D14) strigolactone receptor belongs to the superfamily of α/β-hydrolases, and is known to hydrolyze the bond between the ABC lactone and the D ring. Here we characterized the binding and catalytic functions of RAMOSUS3 (RMS3), the pea (Pisum sativum) ortholog of rice (Oryza sativa) D14 strigolactone receptor. Using new profluorescent probes with strigolactone-like bioactivity, we found that RMS3 acts as a single-turnover enzyme that explains its apparent low enzymatic rate. We demonstrated the formation of a covalent RMS3-D-ring complex, essential for bioactivity, in which the D ring was attached to histidine 247 of the catalytic triad. These results reveal an undescribed mechanism of plant hormone reception in which the receptor performs an irreversible enzymatic reaction to generate its own ligand.

International audience; Strigolactones control various aspects of plant development, including root architecture. Here, we review how strigolactones act in the root and survey the strigolactone specificity of signaling components that affect root development. Strigolactones are a group of secondary metabolites produced in plants that have been assigned multiple roles, of which the most recent is hormonal activity. Over the last decade, these compounds have been shown to regulate various aspects of plant development, such as shoot branching and leaf senescence, but a growing body of literature suggests that these hormones play an equally important role in the root. In this review, we present all known root phenotypes linked to strigolactones. We examine the expression and presence of the main players in biosynthesis and signaling of these hormones and bring together the available information that allows us to explain how strigolactones act to modulate the root system architecture.

Highlight Strigolactones monitor lateral root development in a spatiotemporal manner by an interplay with cytokinin., Strigolactones are important rhizosphere signals that act as phytohormones and have multiple functions, including modulation of lateral root (LR) development. Here, we show that treatment with the strigolactone analog GR24 did not affect LR initiation, but negatively influenced LR priming and emergence, the latter especially near the root–shoot junction. The cytokinin module ARABIDOPSIS HISTIDINE KINASE3 (AHK3)/ARABIDOPSIS RESPONSE REGULATOR1 (ARR1)/ARR12 was found to interact with the GR24-dependent reduction in LR development, because mutants in this pathway rendered LR development insensitive to GR24. Additionally, pharmacological analyses, mutant analyses, and gene expression analyses indicated that the affected polar auxin transport stream in mutants of the AHK3/ARR1/ARR12 module could be the underlying cause. Altogether, the data reveal that the GR24 effect on LR development depends on the hormonal landscape that results from the intimate connection with auxins and cytokinins, two main players in LR development.

International audience; Strigolactones are plant metabolites that act as phytohormones and rhizosphere signals. Whereas most research on unraveling the action mechanisms of strigolactones is focused on plant shoots, we investigated proteome adaptation during strigolactone signaling in the roots of Arabidopsis thaliana. Through large-scale, time-resolved, and quantitative proteomics, the impact of the strigolactone analog rac-GR24 was elucidated on the root proteome of the wild type and the signaling mutant more axillary growth 2 (max2). Our study revealed a clear MAX2-dependent rac-GR24 response: an increase in abundance of enzymes involved in flavonol biosynthesis, which was reduced in the max2-1 mutant. Mass spectrometry-driven metabolite profiling and thin-layer chromatography experiments demonstrated that these changes in protein expression lead to the accumulation of specific flavonols. Moreover, quantitative RT-PCR revealed that the flavonol-related protein expression profile was caused by rac-GR24-induced changes in transcript levels of the corresponding genes. This induction of flavonol production was shown to be activated by the two pure enantiomers that together make up rac-GR24. Finally, our data provide much needed clues concerning the multiple roles played by MAX2 in the roots and a comprehensive view of the rac-GR24-induced response in the root proteome.

Strigolactones (SLs), first identified for their role in parasitic and symbiotic interactions in the rhizosphere, constitute the most recently discovered group of plant hormones. They are best known for their role in shoot branching but, more recently, roles for SLs in other aspects of plant development have emerged. In the last five years, insights into the SL biosynthetic pathway have also been revealed and several key components of the SL signaling pathway have been identified. Here, and in the accompanying poster, we summarize our current understanding of the SL pathway and discuss how this pathway regulates plant development.

International audience; : In vascular plants, strigolactones (SLs) are known for their hormonal role and for their role as signal molecules in the rhizosphere. SLs are also produced by the moss Physcomitrella patens, in which they act as signaling factors for controlling filament extension and possibly interaction with neighboring individuals. To gain a better understanding of SL action at the cellular level, we investigated the effect of exogenously added molecules (SLs or analogs) in moss growth media. We used the previously characterized Ppccd8 mutant that is deficient in SL synthesis and showed that SLs affect moss protonema extension by reducing caulonema cell elongation and mainly cell division rate, both in light and dark conditions. Based on this effect, we set up bioassays to examine chemical structure requirements for SL activity in moss. The results suggest that compounds GR24, GR5, and 5-deoxystrigol are active in moss (as in pea), while other analogs that are highly active in the control of pea branching show little activity in moss. Interestingly, the karrikinolide KAR1, which shares molecular features with SLs, did not have any effect on filament growth, even though the moss genome contains several genes homologous to KAI2 (encoding the KAR1 receptor) and no canonical homologue to D14 (encoding the SL receptor). Further studies should investigate whether SL signaling pathways have been conserved during land plant evolution.

International audience; : Strigolactones (SLs), a group of small carotenoid-derived molecules, were first known for their function in the rhizosphere in both symbiotic and parasitic interactions. Most of the progress for deciphering SL biosynthesis and signalling pathways comes from the use of high branching mutants identified in several species demonstrating that SLs also play a hormonal role in plant development. How SLs are perceived by the different organisms on which they show bioactivity is a current major challenge for the growing SL research community. These molecules very likely predate the colonization of land by plants and represent a fascinating example of signalling molecules involved in key innovations during plant evolution.

International audience; The oxidative cleavage of 4,6-O-benzylidene acetals of glycopyranosides using dimethyldioxirane (DMDO) leads to the corresponding hydroxy-benzoates lent yields. With a Proper choice of the neighboring protecting groups, this oxidative fragmentation provides the 6- or 4-hydroxyl derivatives in a highly regioselective manner.

Gold(I)-catalyzed cycloisomerization of 1,7- and 1,8-enyne propargylic acetates afforded cyclopropyl derivatives containing seven- and eight-membered rings, respectively. This reaction was used for the synthesis of a new allocolchicinoid having a cyclopropane ring fused to the B seven-membered ring at the C6-C7 positions.

Total syntheses of allocolchicines 4 and 5, with the ester functionality in the C-ring at the C10 or C11 positions, is reported. An asymmetric synthesis of (7S)-allocolchicine 5 is also described. The main features included the elaboration of a common intermediate, the AB bicyclic ring system, in which the construction of the seven-membered ring was achieved by an enyne ring-closing metathesis (RCM) reaction. A subsequent Diels–Alder/aromatization sequence afforded the set of functionalized ring-C allocolchicinoids with high regioselectivity. This strategy was also applied for the synthesis of allocolchicine 6, containing an eight-membered B-ring.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

International audience; New allocolchinoids having functionality in the C ring at position C10 or C11 have been synthesized using the enyne ring-closing metathesis (RCM) reaction for construction of the seven-membered ring and a Diels-Alder-aromatization sequence for the elaboration of the aromatic ring C. © 2007 American Chemical Society.

International audience; The synthesis of the tricyclic framework of colchicine has been achieved using a tandem ring-closing metathesis reaction of dienynes as the key step. In this process, both seven-membered rings B and C were formed in one step. Oxidation of tertiary allylic alcohol derived from the tandem metathesis product furnished an intermediate in the total synthesis of colchicine. © 2007 American Chemical Society.

Several dienynes bearing different substituents have been synthesized and subjected to a ring-closing metathesis (RCM) reaction using ruthenium carbene complexes. Dienynes containing a pre-existing ring and a quaternary center attached to the alkyne give the expected tandem metathesis products in high yields. For these substrates, a high selectivity for different ring sizes was achieved by modifying the reactivity of one alkene. In one case, an unusual non-metathetic activity of the second-generation Grubbs catalyst was observed and the cycloisomerization product was obtained as the major product. In the absence of favorable factors, especially when the starting substrates contain hindered alkenes, a long tether chain and/or an ester group on the alkyne part, the tandem process is slowed down or completely impeded. In these cases, dienynes behave like simple enynes and afford initial metathesis products whose further reactions give dimeric compounds.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

International audience; Numerous chemicals, including the xenobiotic 2,5-xylidine, are known to induce laccase production in fungi. The present study was conducted to determine whether the metabolites formed from 2,5-xylidine by fungi could enhance laccase activity. We used purified laccases to transform the chemical and then we separated the metabolites, identified their chemical structure and assayed their effect on enzyme activity in liquid cultures of Trametes. versicolor. We identified 13 oligomers formed from 2,5-xylidine. (4E)-4-(2,5-dimethylphenylimino)-2,5-dimethylcyclohexa-2,5-dienone at 1.25×10−5 M was an efficient inducer, resulting in a nine-fold increase of laccase activity after 3 days of culture. Easily synthesized in one step (67% yield), this compound could be used in fungal bioreactors to obtain a great amount of laccases for biochemical or biotechnological purposes, with a low amount of inducer.

International audience; (Chemical Equation Presented) Acid-catalyzed addition of alcohols to tricyclic dienyl epoxides such as 4 or bicyclic vinyl oxiranes such as 17 exclusively occurred at the vinyl terminus of unsaturated system through a typical SN2' process affording 1,6- and 1,4-dioxygenated derivatives, respectively.

A general procedure for the oxidation of catechin derivatives is described, leading to the introduction of a new hydroxy group at C-6. This procedure has been applied for the synthesis of elephantorrhizol, a natural flavan-3-ol exhibiting a fully substituted cycle A.

This paper describes the synthesis of pyrano-agarofuran tetraol 8. The key step of the synthesis lies in the stereoselectivity encountered in the hydrogenation of precursor 13 because of its peculiar cis-decalinic conformation. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

This paper describes the synthesis of polyhydroxylated decalinic systems through oxidative furan ring opening of 3-(2’-furyl)-2-methoxycarbonylcyclohexadione-4-monoethylene ketal 12 using dimethyl dioxirane (DMDO). The functionalisation of the decalinic product 5, aimed at the synthesis of antifeedant agarofuran sesquiterpenes according to our previously reported strategy, is demonstrated to occur with good stereochemical control of the introduced oxygenated functions, using as a key step an original allylic oxidation by DMDO. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

The synthesis of pyrano-agarofurans is described using as key step the stereoselective epoxidation of a 6α-hydroxy-1,2,3,4,6,7,8,8a-octahydronaphtalene derivative 8 controlled by the configuration of the allylic alcohol at C-6.

In this paper, the construction of the agarofuran tricyclic ring system bearing an hydroxy group at C-4, with the correct configuration at C-4, is described through the rearrangement of the 4,4a α-epoxy 9-benzoyloxy cyperone derivative 11 , readily available from cyperone derivative 5c , under acidic conditions.

Bovine odorant-binding protein (bOBP) is a dimeric lipocalin present in large amounts in the respiratory and olfactory nasal mucosa. The structure of bOBP refined at 2.0-A resolution revealed an elongated volume of electron density inside each buried cavity, indicating the presence of one (or several) naturally occurring copurified ligand(s) (Tegoni et al. (1996) Nat. Struct. Biol. 3, 863-867; Bianchet et al. (1996) Nat. Struct. Biol. 3, 934-939). In the present work, by combining mass spectrometry, x-ray crystallography (1.8-A resolution), and fluorescence, it has been unambiguously established that natural bOBP contains the racemic form of 1-octen-3-ol. This volatile substance is a typical component of bovine breath and in general of odorous body emanations of humans and animals. The compound 1-octen-3-ol is also an extremely potent olfactory attractant for many insect species, including some parasite vectors like Anopheles (Plasmodium) or Glossina (Trypanosoma). For the first time, a function can be assigned to an OBP, with a possible role of bOBP in the ecological relationships between bovine and insect species.

Isoxaflutole is a herbicide activated in soils and plants to its diketonitrile derivative, the active herbicide principle. The diketonitrile derivative undergoes cleavage to the inactive benzoic acid analogue. In this paper, it is established that an oxidative mechanism implicating two successive reactions in the presence of dimethyldioxirane can chemically initiate the cleavage of the diketonitrile. It is also shown that two white rot strains, Phanerochaete chrysosporium and Trametes versicolor, are able to convert the diketonitrile to the acid when cultured in liquid media. This main metabolite amounts to 24.6 and 15.1% of initial herbicide content after 12-15 days of culture. Another polar metabolite represents

At first, this work deals with the synthesis of a novel class of single-component reversible chiral ionic liquids derived from natural aminoacids. Reversibility was demonstrated by NMR, thermogravimetric analysis and differential scanning calorimetry. These compounds were tested as organocatalysts in an asymmetric Michael addition leading to the formation of expected product in moderate yields. Chiral silylamines, precursors to reversible ionic liquids were also evaluated in the synthesis of Warfarin through an asymmetric Michael addition. Good yields were obtained. However, these catalysts have resulted in only low enantioselectivity. Moreover, the use of reversible ionic liquid as a temporary protecting group in glycochemistry, for the synthesis of disaccharides was also implemented. Secondly, some new chiral imidazolinium salts, precursors to NHCs, were synthesized from (S)-pyroglutamic acid, for copper-catalyzed conjugate addition of Grignard reagents to α,β-unsaturated ketones applications. The results have shown moderate enantioselectivity with very good catalytic activity and excellent regioselectivity.; Ce travail de thèse porte, dans un premier temps, sur le développement d'une nouvelle synthèse de liquides ioniques chiraux réversibles, en système mono-composant, à partir d'aminoacides naturels. La réversibilité a été démontrée par RMN, par analyse thermogravimétrique et par calorimétrie différentielle à balayage. Ces composés ont été testés comme catalyseurs organiques dans la réaction d’addition de Michael asymétrique. Des rendements modérés ont été obtenus. Les silylamines chirales, précurseurs des liquides ioniques chiraux réversibles, ont été évaluées dans la synthèse de Warfarine via une addition de Michael asymétrique. De bons rendements ont été obtenus. Toutefois, ces catalyseurs n'ont permis de conduire qu'à de faibles énantiosélectivités. L'utilisation de liquides ioniques réversibles comme groupements protecteurs temporaires en glycochimie, pour la synthèse de disaccharides, a été mise en œuvre. Dans un second temps, de nouveaux sels d'imidazolinium chiraux précurseurs de NHCs ont été synthétisés, à partir de l'acide (S)-pyroglutamique en vue de leur application dans la réaction d'addition conjuguée de cétones α, β-insaturées catalysée au cuivre avec des réactifs de Grignard. Les excès énantiomériques sont modestes mais de bons résultats en termes d’activité catalytique et de régiosélectivité ont été obtenus.

Understanding and exploitation of biological processes, such as symbiotic nitrogen fixation (plant-bacteria) and arbuscular endomycorrhizal symbiosis (plant-fungi), represent important agricultural, ecological and societal interest. The lipo-chitooligosaccharides (LCO) play an essential role in the implementation of these symbioses, it is then important to better understand the mechanisms induced by these signaling molecules, and especially the interaction with host-plant receptors.The chemical syntheses of these molecules are often long, difficult and the final yields are very low, so it could be interesting to obtain biological active analogs more efficiently. Various studies have already shown that a triazole unit could be a saccharide mimic. Furthermore, modelling studies of protein-ligand interactions showed that the monosaccharidic unit II of a LCO-IV could have a less important role in the interaction with the receptor. The project aimed to synthesize these LCO-IV analogs in which unit II was replaced by a triazole link.The strategy was directed towards the synthesis of two glycostructures, a monosaccharide propargylated at C-4 position and a disaccharide with an azide at anomeric position. Various synthetic steps were performed to have access to these two intermediates in good yields. Copper-catalyzed [3+2] cycloaddition gave efficiently the desired triazole unit of tetrasaccharidic analogs. The prior use of adequate protections finally allowed to introduce the desired molecular diversity, a sulphate function at C-6 position of the reducing unit and different lipophilic carbon chains on the amine of the non-reducing unit, and thus to obtain four LCO analogs with very good yields. Competition tests performed on these analogs have shown no affinity for the receptor. A synthetic approach of novel analogs using a C-glycosylation step was then proposed.; La compréhension et l'exploitation des processus biologiques, tels que la symbiose fixatrice d'azote (plante-bactéries) et la symbiose endomycorhizienne à arbuscules (plante-champignons), représentent un intérêt agronomique et écologique majeur. Les lipo-chitooligosaccharides (LCO) jouent un rôle essentiel dans la mise en place de ces deux symbioses. Il est donc important de mieux comprendre les mécanismes induits par ces molécules signal, et notamment l’interaction avec leur récepteur dans les plantes-hôtes.Les synthèses chimiques de ces molécules sont souvent longues, difficiles et les rendements finaux sont très faibles. Il est intéressant de s'intéresser à l'obtention d'analogues biologiquement actifs dont la synthèse serait plus efficace. Différents travaux ont montré qu'un cycle triazole pouvait être un bon mime d'une unité saccharidique. De plus, des travaux de modélisation des interactions protéine-ligand ont permis de supposer que l'unité II d'un LCO-IV pourrait avoir un rôle moins important dans la liaison avec le récepteur. Le but du projet a donc été de réaliser la synthèse de ces analogues de LCO-IV dont l'unité II est remplacée par un lien triazole.La stratégie développée a nécessité la synthèse de deux briques moléculaires, un monosaccharide propargylé en position 4 et un disaccharide comportant un azoture en position anomère. Grâce à la mise au point des différentes étapes de synthèse, ces deux briques ont pu être obtenues avec de bons rendements. La cycloaddition [3+2] catalysée au cuivre a permis d'obtenir le triazole souhaité et les premiers analogues de tétrasaccharides de manière efficace. L'utilisation préalable de protections adéquates a permis d'introduire la diversité moléculaire souhaitée, une fonction sulfate sur la position 6 de l'unité réductrice et différentes chaînes carbonées lipophiles sur l'amine de l'unité non-réductrice. Quatre analogues de LCO ont été obtenus avec de très bons rendements. Les tests de compétitions, effectués sur ces analogues, n'ont montré aucune affinité pour le récepteur. Une approche synthétique de nouveaux analogues par une C-glycosylation a alors été proposée.

Oligosaccharides and glycoconjugates are involved in numerous biological events. However, their synthesis is generally more complex than for other biomolecules. The main challenge is often the generation of the glycosidic bond. For this reason, it is still important to develop efficient and stereoselective glycosylations, which afford glycosides in significant amounts using new donors. These reactions are even more attractive if the promoter used is cheap, non-toxic and environmentally friendly, like iron salts. In this context, the direct synthesis of b-glycosides of N-acetyl-D-glucosamine using catalytic iron triflate(III) has been developed. This glycosylation can be performed under microwave irradiation or in continuous flow. The microwave-assisted conditions were then extended to the synthesis of complex N-glycan mimics. This synthesis is based on a polyglycosylation reaction using an iron(III) triflate catalysis coupled to another glycosylation or a click reaction to introduce a functionalized linker. Finally, an a-mannosylation promoted by iron(III) triflate has been developed. This glycosylation, performed under microwave irradiation, is completely stereoselective, even without neighbouring group participation.; Les oligosaccharides et les glycoconjugués jouent des rôles essentiels dans de nombreux processus biologiques. Cependant, leur synthèse est plus complexe que la majorité des autres biomolécules. Le principal défi réside souvent dans la formation de la liaison glycosidique. Il est donc toujours nécessaire de développer des réactions de glycosylation efficaces et totalement stéréosélectives, utilisant de nouveaux donneurs et permettant d'accéder à des structures glycosidiques à différentes échelles. Ces réactions sont d'autant plus intéressantes si elles utilisent des promoteurs peu chers, peu toxiques et peu dangereux pour l'environnement, comme des sels de fer. Dans ce cadre, la formation directe de b-glycosides de la N-acétyl-D-glucosamine par catalyse au triflate de fer(III) a été étudiée. Cette glycosylation peut être réalisée sous irradiation micro-ondes ou en flux continu. Les conditions d'activation sous micro-ondes ont ensuite été étendues à la synthèse de motifs de N-glycanes complexes. Cette synthèse consiste en une étape de polyglycosylation au triflate de fer(III), combinée à une étape d'introduction d'un lien moléculaire, via une nouvelle glycosylation ou une réaction de la chimie click. Enfin, une a-mannosylation utilisant le triflate de fer(III) a été découverte et mise au point. Cette glycosylation, réalisée sous activation micro-ondes, est totalement stéréosélective, même en l'absence de groupement participant.

Rhizobia symbiosis and arbuscular mycorrhiza symbiosis have an agrobiological and ecological interest because they allow plants to grow on aride and infertile soil. Recently, the symbiotic signals (« Myc factors ») were identified as a mixture of lipo-chitooligosaccharides (LCOs). The preparation of Myc factor [Myc-IV (C16:0, S)], the most abundant and bioactive, was carried out using a blockwise synthesis. Dimethyldioxirane for a regioselective oxidative cleavage of benzylidene acetals and an odorless and few toxic thiol to form thioglycoside donors were employed. To eliminate the laborious purifications of oligosaccharides by chromatography on silica gel after each glycosylation step, we developped an ionic liquid supported strategy. The ionic liquid part changes the physico-chimical properties of the expected product and we isolated the glycostructures by simple phase-extractions. The chitooligosaccharide (CO-IV), key intermediate for the synthesis of non-sulfated lipo-chitooligosaccharides or TMG-chitotriomycin, was obtained by this strategy.; La symbiose à Rhizobia ainsi que la symbiose endomycorhizienne à arbuscules, présentes dans la rhizosphère, possèdent un intérêt agrobiologique et écologique majeur ; elles permettent aux plantes de croître naturellement sur un sol aride et peu fertile. Il a été démontré récemment que les signaux (facteurs « Myc ») impliqués dans la mise en place de la symbiose endomycorhizienne à arbuscules appartiennent à la famille des lipo-chitooligosaccharides. Une nouvelle synthèse du facteur de mycorhization [Myc-IV (C16:0, S)], le plus abondant et bioactif, a été effectuée en utilisant une stratégie de synthèse par blocs utilisant des méthodes robustes de glycosylation, le diméthyldioxirane pour l’ouverture oxydante régiosélective des acétals de benzylidène et l’emploi d’un thiol peu toxique et peu odorant pour former les donneurs thioglycosides. Étant donné la purification laborieuse par chromatographie sur gel de silice des oligosaccharides après les étapes de glycosylation, une nouvelle méthode utilisant des liquides ioniques supportés a été appliquée permettant de modifier les propriétés physico-chimiques des saccharides. Les produits sont purifiés par de simples lavages grâce à ce motif ionique présent en position anomérique. Le chitooligosaccharide (CO-IV), intermédiaire clef pour la synthèse de lipo-chiooligosaccharides non sulfatés d’intérêts ou de la TMG-chitotriomycin, a ainsi été obtenu.

Arbuscular mycorrhiza (AM) is a root endosymbiosis between plants and fungi. It has an agrobiological interest and a crucial ecological importance because it allows plants to grow on aride and infertile soil. Recently, the structure of the symbiotic signal "Myc factor" was identified as a mixture of lipochitooligosaccharides (LCOs). In order to propose a new synthesis of LCOs, we developed two green methodologies in glycochemistry. We performed the oxidative cleavage of 4,6-O-benzylidene acetals of various glycopyranosides (gluco, manno and galacto series) with dimethyldioxirane (DMDO) and its regioselective control with a suitable protecting group at position 3. We investigated the formation of β-glycoside of N-acetyl-D-glucosamine using catalytic iron (III) triflate. The reaction can be performed using microwave irradiation or, for scale-up synthesis, flow chemistry using Vapourtec® minifluidic system. We establish a new strategy for the total synthesis of the most abundant Myc factor [Myc-IV (C16:0, S)]. We used odorless and few toxic MbpSH reagent to introduce the activated thio residue involved in two glycosylation reactions. The disaccharide acceptor precursor of the reducing end was obtained after oxidative cleavage of the 4,6-O-benzylidene moiety by DMDO., Les symbioses bactérie-légumineuse (nodulation) et champignon-plante (mycorhization) présentent un intérêt agrobiologique et écologique majeur ; elles permettent aux plantes de croître naturellement sur un sol aride et peu fertile. Il a été démontré très récemment que les signaux impliqués dans la mise en place de la symbiose endomycorhizienne à arbuscule (facteurs "Myc") sont très proches de ceux de la nodulation. Il s'agit de molécules appartenant à la famille des lipo-chitooligosaccharides. Afin de réaliser la synthèse de ces molécules, deux nouvelles méthodologies ont été développées. L'ouverture oxydante d'acétals de 4,6-O-benzylidène de plusieurs glycopyranosides (en série gluco, galacto et manno) par le diméthyldioxirane (DMDO) a été étudiée. Le contrôle de la régiosélectivité a été effectué grâce au groupement protecteur introduit sur la fonction alcool de la position 3. La formation directe de β-glycosides de la N-acétyl-D-glucosamine par catalyse au triflate de fer (III) a été étudiée. La réaction a été menée sous irradiation micro-ondes ou en flux continu (système minifluidique Vapourtec®). Une nouvelle stratégie pour la synthèse du facteur [Myc-IV (C16:0, S)] a ensuite été établie. Nous avons utilisé un réactif peu toxique et non odorant pour introduire le motif thio nécessaire à la formation de deux liaisons glycosidiques. Le disaccharide précurseur de l'unité réductrice a été obtenu grâce à la première méthodologie développée au cours de cette thèse.

This Ph.D. work has been centred on the elaboration of a new synthetic strategy in goal to obtain analogues of natural strigolactones, apocarotenoids with various biological activities of agronomic interests: chemical mediators implicated in the endomycorrhizal symbiosis and a new class of plant hormone controlling the plant architecture.The synthetic strategy is based on the sequence of two key reactions, which are ring closing metathesis (RCM) and atom transfer radical cyclisation (ATRC). First, a rapid and efficient access to the synthetic precursors has been developed and after optimisation of the RCM / ATRC sequence, several analogues functionnalised at the C4 position were obtained after judicious steps. Other bioisoters were obtained with variations on the C ring. On the basis of the elaborated synthetic pathway, the first asymmetric synthesis of Solanacol was successfully achieved conducting to the determination of the relative stereochemistry at C2’ position and its absolute configuration. The biological evaluations of the synthesized molecules in the different models were also described.; Ce travail de thèse présente la mise au point d’une nouvelle stratégie de synthèse en vue de l’obtention d’analogues des strigolactones, apocaroténoïdes possédant de multiples activités biologiques d’intérêt agronomique : médiateurs chimiques intervenant dans la mise en place de la symbiose endomycorhizienne et nouvelle classe d’hormone végétale contrôlant l’architecture de la plante.La stratégie de synthèse est basée sur l’utilisation d’une séquence de deux réactions clefs qui sont une métathèse cyclisante d’oléfine (RCM) et une cyclisation radicalaire avec transfert d’atome catalysée par un métal de transition (ATRC). Tout d’abord, une synthèse rapide et efficace des précurseurs a été développée et après optimisation de la séquence RCM / ATRC, divers analogues fonctionnalisés en position C4 ont été obtenus après aménagements fonctionnels. D’autres bioisostères des strigolactones naturelles ont été synthétisés par variation au niveau du cycle C. En se basant sur la voie synthétique précédemment élaborée, la première synthèse asymétrique du Solanacol a été effectuée permettant la détermination de sa stéréochimie relative en C2’ et sa configuration absolue. L’évaluation des activités biologiques dans les différents modèles des composés synthétisés est aussi décrite.