Scavenging iron: a novel mechanism of plant immunity activation by microbial siderophores.

Siderophores are specific ferric iron chelators synthesized by virtually all microorganisms in response to iron deficiency. We have previously shown that they promote infection by the phytopathogenic enterobacteria Dickeya dadantii and Erwinia amylovora. Siderophores also have the ability to activate plant immunity. We have used complete Arabidopsis transcriptome microarrays to investigate the global transcriptional modifications in roots and leaves of Arabidopsis (Arabidopsis thaliana) plants after leaf treatment with the siderophore deferrioxamine (DFO). Physiological relevance of these transcriptional modifications was validated experimentally. Immunity and heavy-metal homeostasis were the major processes affected by DFO. These two physiological responses could be activated by a synthetic iron chelator ethylenediamine-di(o-hydroxyphenylacetic) acid, indicating that siderophores eliciting activities rely on their strong iron-chelating capacity. DFO was able to protect Arabidopsis against the pathogenic bacterium Pseudomonas syringae pv tomato DC3000. Siderophore treatment caused local modifications of iron distribution in leaf cells visible by ferrocyanide and diaminobenzidine-H2O2 staining. Metal quantifications showed that DFO causes a transient iron and zinc uptake at the root level, which is presumably mediated by the metal transporter iron regulated transporter1 (IRT1). Defense gene expression and callose deposition in response to DFO were compromised in an irt1 mutant. Consistently, plant susceptibility to D. dadantii was increased in the irt1 mutant. Our work shows that iron scavenging is a unique mechanism of immunity activation in plants. It highlights the strong relationship between heavy-metal homeostasis and immunity.

Cyclooctane metathesis catalyzed by silica-supported tungsten pentamethyl [(≡SiO)W(Me)5]: distribution of macrocyclic alkanes.

Metathesis of cyclic alkanes catalyzed by the new surface complex [(≡SiO)W(Me)5] affords a wide distribution of cyclic and macrocyclic alkanes. The major products with the formula C(n)H(2n) are the result of either a ring contraction or ring expansion of cyclooctane leading to lower unsubstituted cyclic alkanes (5≤n≤7) and to an unprecedented distribution of unsubstituted macrocyclic alkanes (12≤n≤40), respectively, identified by GC/MS and by NMR spectroscopies.

Bio-inspired formal synthesis of hirsutellones A-C featuring an electrophilic cyclization triggered by remote Lewis acid-activation.

A bio-inspired strategy was used to complete the formal synthesis of the antitubercular hirsutellone B and congeners A and C, through construction of its decahydrofluorene core from a linear polyene strand activated at both ends by a silyl enol ether and an allyl acetate. Our synthesis features a key electrophilic cyclization, starting with the remote activation (by [Yb(OTf)3] or BF3·OEt2) of the allyl acetate and stereoselectively affording the C ring. This was followed by an intramolecular Diels-Alder reaction to get the tricyclic core of the natural product. The stereoselective reduction of the resulting ketone towards the formal intermediate was critical to the success of this strategy.

Simple addition of silica to an alkane solution of a Wilkinson WMe6 or Schrock W alkylidyne complex gives an active complex for saturated and unsaturated hydrocarbon metathesis.

The addition of partially dehydroxylated silica (PDS) to a solution of the Wilkinson WMe6 as well as the Schrock W neopentylidyne tris neopentyl complex catalyzes linear or cyclic alkanes to produce respectively a distribution of linear alkanes from methane up to triacontane or a mixture of cyclic and macrocyclic hydrocarbons. This single catalytic system transforms also linear α-olefins into higher and lower homologues via an isomerization/metathesis mechanism (ISOMET). This complex is also efficient towards functionalized olefins. Unsaturated fatty acid esters (FAEs) are converted into diesters corresponding to self-metathesis products.

Chemistry and biology of non-tetramic gamma-hydroxy-gamma-lactams and gamma-alkylidene-gamma-lactams from natural sources.

Natural products containing non-tetramic gamma-hydroxy-gamma-lactams and gamma-alkylidene-gamma-lactams are usually but not exclusively derived from the mixed polyketide-non-ribosomal peptide biosynthetic pathway. Often they are fungal metabolites, although some plant- and marine-derived exceptions exist. Owing to their unique structures and biological properties, they have gained interest in the chemical and biological communities. In this review, we aim to emphasize the structural originality of these compounds, their biological properties and the synthetic efforts developed to reach them; 157 references are cited.