Site‐Selective trans‐Hydrostannation of 1,3‐ and 1,n‐Diynes: Application to the Total Synthesis of Typhonosides E and F, and a Fluorinated Cerebroside Analogue

Propargyl alcohols are privileged substrates for stereochemically unorthodox trans‐hydrostannation reactions catalyzed by [Cp*RuCl]4 (Cp*=pentamethylcyclopentadienyl), because an incipient hydrogen bond between the ‐OH group and the polarized [Ru‐Cl] unit assists substrate binding. For this very reason, it is also possible to subject diyne derivatives carrying one ‐OH group to site‐selective stannylation, even if the acetylene units are conjugated and hence, electronically coupled. An unusual temperature dependence was observed in that heating tends to improve site‐selectivity, whereas per‐stannylation 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 1,3‐diyne substrate by two metal centers. The preparative relevance of site‐selective trans‐hydrostannation 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 late‐stage modification of a bioactive target compound

A használatalapú biztosítás múltja, jelene és jövője

[Cp*RuCl]₄ (1) has previously been shown to be the precatalyst of choice for stereochemically unorthodox trans-hydrometalations of internal alkynes. Experimental and computational data now prove that the alkyne primarily acts as a four-electron donor ligand to the catalytically active metal fragment [Cp*RuCl] but switches to adopt a two-electron donor character once the reagent R₃MH (M = Si, Ge, Sn) enters the ligand sphere. In the stereodetermining step the resulting loaded complex evolves via an inner-sphere mechanism into a ruthenacyclopropene which swiftly transforms into the product. In accord with the low computed barriers, spectral and preparative data show that the reaction is not only possible but sometimes even favored at low temperatures. Importantly, such trans-hydrometalations are distinguished by excellent levels of regioselectivity when unsymmetrical alkynes are used that carry an −OH or −NHR group in vicinity of the triple bond. A nascent hydrogen bridge between the protic substituent and the polarized [Ru–Cl] unit imposes directionality onto the ligand sphere of the relevant intermediates, which ultimately accounts for the selective delivery of the R₃M– group to the acetylene C-atom proximal to the steering substituent. The interligand hydrogen bonding also allows site-selectivity to be harnessed in reactions of polyunsaturated compounds, since propargylic substrates bind more tightly than ordinary alkynes; even the electronically coupled triple bonds of conjugated 1,3-diynes can be faithfully discriminated as long as one of them is propargylic. Finally, properly positioned protic sites lead to a substantially increased substrate scope in that they render even 1,3-enynes, arylalkynes, and electron-rich alkynylated heterocycles amenable to trans-hydrometalation which are otherwise catalyst poisons

Reactivity of Gold Hydrides: O2 Insertion into the Au–H Bond

Dioxygen reacts with the gold(I) hydride (IPr)AuH under insertion to give the hydroperoxide, (IPr)AuOOH, a long-postulated reaction in gold catalysis and the first demonstration of O2 activation by Au-H in a well-defined system. Subsequent condensation gave the peroxide (IPr)Au-OO-Au(IPr) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazole-2-ylidene). The reaction kinetics are reported, as well as the reactivity of Au(I) hydrides with radical scavengers

Relating different Polynomial-LWE problems

In this paper we focus on Polynomial Learning with Errors (PLWE). This problem is parametrized by a polynomial and we are interested in relating the hardness of the $\text{PLWE}^f$ and $\text{PLWE}^h$ problems for different polynomials $f$ and $h$. More precisely, our main result shows that for a fixed monic polynomial $f$, $\text{PLWE}^{f\circ g}$ is at least as hard as $\text{PLWE}^f$, in both search and decision variants, for any monic polynomial $g$. As a consequence, $\text{PLWE}^{\phi_n}$ is harder than $\text{PLWE}^{f},$ for a minimal polynomial $f$ of an algebraic integer from the cyclotomic field $\mathbb{Q}(\zeta_n)$ with specific properties. Moreover, we prove in decision variant that in the case of power-of-2 polynomials, $\text{PLWE}^{\phi_n}$ is at least as hard as $\text{PLWE}^f,$ for a minimal polynomial $f$ of algebraic integers from the $n$th cyclotomic field with weaker specifications than those from the previous result

Structure from motion photogrammetry in forestry : a review

AbstractPurpose of ReviewThe adoption of Structure from Motion photogrammetry (SfM) is transforming the acquisition of three-dimensional (3D) remote sensing (RS) data in forestry. SfM photogrammetry enables surveys with little cost and technical expertise. We present the theoretical principles and practical considerations of this technology and show opportunities that SfM photogrammetry offers for forest practitioners and researchers.Recent FindingsOur examples of key research indicate the successful application of SfM photogrammetry in forestry, in an operational context and in research, delivering results that are comparable to LiDAR surveys. Reviewed studies have identified possibilities for the extraction of biophysical forest parameters from airborne and terrestrial SfM point clouds and derived 2D data in area-based approaches (ABA) and individual tree approaches. Additionally, increases in the spatial and spectral resolution of sensors available for SfM photogrammetry enable forest health assessment and monitoring. The presented research reveals that coherent 3D data and spectral information, as provided by the SfM workflow, promote opportunities to derive both structural and physiological attributes at the individual tree crown (ITC) as well as stand levels.SummaryWe highlight the potential of using unmanned aerial vehicles (UAVs) and consumer-grade cameras for terrestrial SfM-based surveys in forestry. Offering several spatial products from a single sensor, the SfM workflow enables foresters to collect their own fit-for-purpose RS data. With the broad availability of non-expert SfM software, we provide important practical considerations for the collection of quality input image data to enable successful photogrammetric surveys

Zur Betrachtung manipulationsbedingter Belastungsreaktionen in den Vitalparametern eines sehr früh geborenen Kindes

Hintergrund: Ziel der Diplomarbeit war es, die physiologischen Reaktionen eines sehr frühgeborenen Kindes auf Routinemaßnahmen zu untersuchen. Veränderungen der Herzfrequenz, Atemfrequenz und der Sauerstoffsättigung, die oft als Überlastungsindikatoren herangezogen werden, wurden einer genaueren Betrachtung unterzogen. Hierbei war eine Prüfung hinsichtlich signifikanter Veränderungen zwischen den Zeiteinheiten vor, während und nach den Manipulationen von Interesse. Neben einer Erörterung der Phänomene Stress und Schmerzen bei Frühgeborenen wird in der Arbeit ebenfalls ein Einblick über Ausmaß und Inhalt von Manipulationen gegeben, mit denen frühgeborene Kinder auf der Intensivstation konfrontiert sind. Methode: Auf der neonatologischen Intensivstation der Charité in Berlin wurde eine Beobachtungsstudie an einem frühgeborenen Kind (26 SSW, 6…g) durchgeführt. Jede Manipulation am Kind sowie die korrespondierenden Vitalparameter wurden aufgezeichnet und statistisch ausgewertet (Friedman-Test, Wilcoxon-Test). Ergebnisse: Bei den betrachteten Vitalparametern ließen sich zwischen den drei Zeitfenstern signifikante Veränderungen nachweisen (Herzfrequenz p = 0.01, Atemfrequenz p = 0.00, Sauerstoffsättigung p = 0.00), die einen für Belastungsreaktionen typischen Verlauf zeigten. Die 96 beobachteten Handlungen ließen sich in sechs übergeordnete Kategorien unterteilen. Fazit: Die untersuchten Parameter sind reliable Indikatoren für die Stressbelastung Frühgeborener. Durch die Untersuchung konnten ebenfalls die Möglichkeiten und Begrenzungen der Anwendung einer systematischen Beobachtung auf der neonatologischen Intensivstation dargestellt werden.Background: The aim of the thesis for a degree was to investigate the physiological responses of a very preterm infant to procedures that are routinely performed in intensive care nurseries. Changes in heart rate, respiration rate and oxygen saturation, which are usually used as stress indicators, were examined. The values of the three measures during the procedures were compared with values before and after the procedures. Beside a discussion of stress and pain in preterm infants, the diploma dissertation outlines the handlings to which preterm infants are exposed at the neonatal intensive care unit. Design: A very preterm infant (26 GW, 6…g) was observed in the neonatal intensive care unit of the Charité Hospital in Berlin. Each manipulation on the child and the corresponding physiological responses were recorded and evaluated (Friedman-test, Wilcoxon-test). Results: Significant differences were found among pre-, peri- and post - procedures for all three outcome measures (heart rate: p = 0.01, respiration rate: p = 0.00, oxygen saturation: p = 0.00), which showed a stress characteristic course. In total, 96 manipulations were observed which could be subdivided into six superior categories. Conclusion: The examined physiological responses appear to be reliable indices of stress on a very preterm infant. The examination showed as well the possibilities and limitations of an observation study in the NICU environment

Bis(dimethylsilyl)amide complexes of the alkaline-earth metals stabilized by β-Si-H agostic interactions: synthesis, characterization, and catalytic activity

International audienceThe syntheses of the homoleptic compounds Ae[N(SiMe2H)2]2(THF)x (Ae = Ca, x = 1, 2; Sr, x = 2/3, 3; Ba, x = 0, 4) are reported. They can be prepared by salt metathesis involving the alkaline-earth metal iodides and KN(SiMe3)2 (1) or by transamination between Ae[N(SiMe3)2]2(THF)2 and HN(SiMe2H)2. These precursors constitute convenient starting materials for the subsequent preparation of {LnO}AeN(SiMe2H)2 heteroleptic complexes of the large alkaline-earth metals, as exemplified by the syntheses of {LO3}AeN(SiMe2H)2 ({LO3}− = 2-{(1,4,7,10-tetraoxa-13-azacyclopentadecan-13-yl)methyl}-4,6-di-tert-butylphenolate; Ae = Ca, 5; Sr, 6; Ba, 7). Both homo- and heteroleptic complexes are stabilized in the solid state by secondary β-Si−H agostic interactions. The structures of the kinetically stable {LO3}BaN(SiMe2H)2 (7) and those of its potassium synthetic precursors 1 and {LO3}K*KN(SiMe2H)2 (8) are described, and the catalytic activity of the heteroleptic complexes in the ring-opening polymerization of lactide is presented

Simulation of Left Atrial Function Using a Multi-Scale Model of the Cardiovascular System

During a full cardiac cycle, the left atrium successively behaves as a reservoir, a conduit and a pump. This complex behavior makes it unrealistic to apply the time-varying elastance theory to characterize the left atrium, first, because this theory has known limitations, and second, because it is still uncertain whether the load independence hypothesis holds. In this study, we aim to bypass this uncertainty by relying on another kind of mathematical model of the cardiac chambers. In the present work, we describe both the left atrium and the left ventricle with a multi-scale model. The multi-scale property of this model comes from the fact that pressure inside a cardiac chamber is derived from a model of the sarcomere behavior. Macroscopic model parameters are identified from reference dog hemodynamic data. The multi-scale model of the cardiovascular system including the left atrium is then simulated to show that the physiological roles of the left atrium are correctly reproduced. This include a biphasic pressure wave and an eight-shaped pressure-volume loop. We also test the validity of our model in non basal conditions by reproducing a preload reduction experiment by inferior vena cava occlusion with the model. We compute the variation of eight indices before and after this experiment and obtain the same variation as experimentally observed for seven out of the eight indices. In summary, the multi-scale mathematical model presented in this work is able to correctly account for the three roles of the left atrium and also exhibits a realistic left atrial pressure-volume loop. Furthermore, the model has been previously presented and validated for the left ventricle. This makes it a proper alternative to the time-varying elastance theory if the focus is set on precisely representing the left atrial and left ventricular behaviors