109 research outputs found
SiteâSelective transâHydrostannation of 1,3â and 1,nâDiynes: Application to the Total Synthesis of Typhonosidesâ E and F, and a Fluorinated Cerebroside Analogue
Propargyl alcohols are privileged substrates for stereochemically unorthodox transâhydrostannation reactions catalyzed by [Cp*RuCl]4 (Cp*=pentamethylcyclopentadienyl), because an incipient hydrogen bond between the âOH group and the polarized [RuâCl] unit assists substrate binding. For this very reason, it is also possible to subject diyne derivatives carrying one âOH group to siteâselective stannylation, even if the acetylene units are conjugated and hence, electronically coupled. An unusual temperature dependence was observed in that heating tends to improve siteâselectivity, whereas perâstannylation is favored when the reaction is carried out in the cold. This counterintuitive trend can be rationalized based on spectroscopic data; additional support comes from the isolation of the unusual bimetallic complex 11. The bridging fulvene and enynyl ligands in 11 are thought to reflect an interligand redox isomerization process likely triggered by synchronous activation of the 1,3âdiyne substrate by two metal centers. The preparative relevance of siteâselective transâhydrostannation is illustrated by the total synthesis of two members of the typhonoside series of glycolipids, which are endowed with neuroprotective properties. Moreover, the preparation of a fluoroalkene sphingosine analogue shows that the tin residue also serves as a versatile handle for lateâstage modification of a bioactive target compound
A Declarative Paradigm for Robust Cumulative Scheduling
International audienceThis paper investigates cumulative scheduling in uncertain environments, using constraint programming. We present a new declarative characterization of robustness, which preserves solution quality.We highlight the significance of our framework on a crane assignment problem with business constraints
Artificially decreasing cortical tension generates aneuploidy in mouse oocytes
Human and mouse oocytesâ developmental potential can be predicted by their mechanical
properties. Their development into blastocysts requires a specific stiffness window. In this
study, we combine live-cell and computational imaging, laser ablation, and biophysical
measurements to investigate how deregulation of cortex tension in the oocyte contributes to
early developmental failure. We focus on extra-soft cells, the most common defect in a
natural population. Using two independent tools to artificially decrease cortical tension, we
show that chromosome alignment is impaired in extra-soft mouse oocytes, despite normal
spindle morphogenesis and dynamics, inducing aneuploidy. The main cause is a cytoplasmic
increase in myosin-II activity that could sterically hinder chromosome capture. We describe
here an original mode of generation of aneuploidies that could be very common in oocytes
and could contribute to the high aneuploidy rate observed during female meiosis, a leading
cause of infertility and congenital disorders
Highly efficient synthesis of the tricyclic core of Taxol by cascade metathesis
An efficient enantioselective synthesis of the ABC tricyclic core of the anticancer drug Taxol is reported. The key step of this synthesis is a cascade metathesis reaction, which leads in one operation to the required tricycle if appropriate fine-tuning of the dienyne precursor is performed
Adventive hydrothermal circulation on Stromboli volcano (Aeolian Islands, Italy) revealed by geophysical and geochemical approaches: Implications for general fluid flow models on volcanoes
International audienceOn March 15th 2007 a paroxysmal explosion occurred at the Stromboli volcano. This event generated a large amount of products, mostly lithic blocks, some of which impacted the ground as far as down to 200 m a.s.l., about 1.5 km far away from the active vents. Two days after the explosion, a new vapour emission was discovered on the north-eastern flank of the volcanic edifice, at 560 m a.s.l., just above the area called "Nel Cannestrà ". This new vapour emission was due to a block impact. In order to investigate the block impact area to understand the appearance of the vapour emission, we conducted on May 2008 a multidisciplinary study involving Electrical Resistivity Tomography (ERT), Ground Penetrating Radar (GPR), Self-Potential (SP), CO2 soil diffuse degassing and soil temperature surveys. This complementary data set revealed the presence of an anomalous conductive body, probably related to a shallow hydrothermal level, at about 10-15 m depth, more or less parallel to the topography. It is the first time that such a hydrothermal fluid flow, with a temperature close to the water boiling point (76 °C) has been evidenced at Stromboli at this low elevation on the flank of the edifice. The ERT results suggest a possible link between (1) the main central hydrothermal system of Stromboli, located just above the plumbing system feeding the active vents, with a maximum of subsurface soil temperature close to 90 °C and limited by the NeoStromboli summit crater boundary and (2) the investigated area of Nel Cannestrà , at ~ 500 m a.s.l., a buried eruptive fissure active 9 ka ago. In parallel, SP and CO2 soil diffuse degassing measurements suggest in this sector at slightly lower elevation from the block impact crater a magmatic and hydrothermal fluid rising system along the N41° regional fault. A complementary ERT profile, on May 2009, carried out from the NeoStromboli crater boundary down to the block impact crater displayed a flank fluid flow apparently connected to a deeper system. The concept of shallow hydrothermal level have been compared to similar ERT results recently obtained on Mount Etna and La Fossa cone of Vulcano. This information needs to be taken into account in general fluid flow models on volcanoes. In particular, peripheral thermal waters (as those bordering the north-eastern coast of Stromboli) could be contaminated by hydrothermal and magmatic fluids coming from regional faults but also from the summit
- âŠ