This review discusses the tertiary phosphines possessing various chiral skeletons that have been used in asymmetric nucleophilic organocatalytic reactions, including annulations of allenes, alkynes, ...and Morita-Baylis-Hillman (MBH) acetates, carbonates, and ketenes with activated alkenes and imines, allylic substitutions of MBH acetates and carbonates, Michael additions, γ-umpolung additions, and acylations of alcohols.
The nine-membered ring-bearing bicyclo5.2.2tetrahydrooxonines frameworks have enantioselectively been constructed via a tandem 3 + 2 cycloaddition/Cope rearrangement reaction of vinylethylene ...carbonates (VECs) with coumalates or pyrones. Under mild conditions, palladium-catalyzed asymmetric tandem reaction of various substituted VECs and coumalates or pyrones proceeds smoothly to produce the corresponding medium-sized heterocyclic compounds in high yields with very high enantioselectivities. Moreover, the reaction on the gram scale and further diverse transformations of the products were workable. The reaction mechanism was investigated through control experiments and DFT calculations, which show the reaction proceeds via a tandem 3 + 2 cycloaddition/Cope rearrangement pathway rather than via a 5 + 4 cycloaddition pathway.
Inhibition of Mek/Erk signaling by pharmacological Mek inhibitors promotes self-renewal and pluripotency of mouse embryonic stem cells (ESCs). Intriguingly, Erk signaling is essential for human ESC ...self-renewal. Here we demonstrate that Erk signaling is critical for mouse ESC self-renewal and genomic stability. Erk-depleted ESCs cannot be maintained. Lack of Erk leads to rapid telomere shortening and genomic instability, in association with misregulated expression of pluripotency genes, reduced cell proliferation, G1 cell-cycle arrest, and increased apoptosis. Erk signaling is also required for the activation of differentiation genes but not for the repression of pluripotency genes during ESC differentiation. Furthermore, we find an Erk-independent function of Mek, which may explain the diverse effects of Mek inhibition andErkknockout on ESC self-renewal. Together, in contrast to the prevailing view, Erk signaling is required for telomere maintenance, genomic stability, and self-renewal of mouse ESCs.
In this paper we describe the phosphine-catalyzed 3 + 2, 3 + 3, 4 + 3, and 3 + 2 + 3 annulations of azomethine imines and allenoates. These processes mark the first use of azomethine imines in ...nucleophilic phosphine catalysis, producing dinitrogen-fused heterocycles, including tetrahydropyrazolo-pyrazolones, -pyridazinones, -diazepinones, and -diazocinones. Counting the two different reaction modes in the 3 + 3 cyclizations, there are five distinct reaction pathwaysthe choice of which depends on the structure and chemical properties of the allenoate. All reactions are operationally simple and proceed smoothly under mild reaction conditions, affording a broad range of 1,2-dinitrogen-containing heterocycles in moderate to excellent yields. A zwitterionic intermediate formed from a phosphine and two molecules of ethyl 2,3-butadienoate acted as a 1,5-dipole in the annulations of azomethine imines, leading to the 3 + 2 + 3 tetrahydropyrazolo-diazocinone products. The incorporation of two molecules of an allenoate into an eight-membered-ring product represents a new application of this versatile class of molecules in nucleophilic phosphine catalysis. The salient features of this protocolthe facile access to a diverse range of nitrogen-containing heterocycles and the simple preparation of azomethine imine substratessuggest that it might find extensive applications in heterocycle synthesis.
H-steel all-bolted connection steel frame structures with heat preservation and decoration composite wall boards were investigated and the seismic performances of three scaled specimens were studied. ...The failure modes, hysteresis curves, bearing capacity, ductility, energy dissipation capacity, stiffness degradation and strain distribution were discussed. The calculation method of structural theoretical internal force was presented. The results showed that the overall structural seismic performance was better, and the structural ductility met the demands of elastic-plastic inter-story drift angle for seismic design. The H-steel weak-axis connection structure obtained better energy dissipation capacity, and its bearing capacity and stiffness were slightly different from the strong-axis connection. The heat preservation and decoration performance of composite wallboard and the all-bolted connection of the steel frame realized prefabrication during the whole construction period. The plastic hinge of the steel beam can be moved outwards because of the L-angles, which effectively avoids stress concentration in joint areas and expands the plastic hinge range. The errors between the theoretical structural capacity calculated by the plastic analysis method and the test results were within 2.44%. In addition, structural failure mechanisms and bearing capacities were verified by the finite element (FE) analysis, and the effects of the main parameters on the structures were investigated. The FE verification results were the same as in the test. The research results provide theoretical support and technical guidance for the application of thermal insulation and decorative composite wall panels in H-shaped steel all-bolted steel frames.
A copper‐catalyzed enantioselective three‐component difunctionalization of allenes with seven‐membered cyclic imines and bis(pinacolato)diboron (B2(Pin)2) to approach functionalized ...dibenzob,f1,4oxazepine derivatives is developed. The chiral products are obtained in up to 81% yield, >20:1 dr, and 98% ee when either a chiral diphosphine ligand or a chiral ferrocenyl‐based P,N‐ligand is used. Furthermore, the reaction exhibits reversed diastereoselectivities when the chiral diphosphine ligand and the chiral P,N‐ligand are used respectively.
A silver-catalyzed three-component difunctionalization of alkenes by using 2-amino- and 2-hydroxy-1,4-naphthoquinone derivatives as the radical-trapping reagents is reported. Various alkenes and ...2-amino- or 2-hydroxy-1,4-naphthoquinones with diverse structures and electronic properties are applied to the reaction. The methodology provides an alternative method to access CF3-functionalized alkyl-substituted quinone derivatives which are prevalent structures in bioactive molecules. Furthermore, a plausible radical pathway for the reaction is proposed based on results from primary control experiments.
A diastereoselective copper and NHC-ligand-catalyzed three-component difunctionalization of allenes with bis(pinacolato)diboron and 2H-azirines to afford borylated allylaziridines is described. The ...reaction exhibits complete diastereoselectivity and good yields, and the further chlorination of the corresponding borylated products was also performed. It is believed that the high ring-strain force of 2H-azirines facilitates the reaction. More chemical transformations of borylated allylaziridines are also reported.
In order to study the mechanical property degradation rule of Q690 high-strength steel in the ocean wave splash area, the rusted specimen is obtained by indoor damp heat surrounding soaking ...environment corrosion test. The scanning electron microscopy, uniaxial tensile and cyclic loading tests of corroded steel are performed. This paper analyzes the steel from elastic modulus, yield strength, ductility and law of hysteresis degradation under different corrosion cycles and establishes the constitutive model of HSS. The results show that the appearance of HSS is obviously affected by the corrosion cycle. With the increase of the corrosion cycle, reddish-brown flaky corrosion products are formed on the surface of the steel and there are obvious corrosion pits. After 100 days of corrosion, the corrosion rate of steel reached 7.21%; the elastic modulus and yield strength under uniaxial tension load decreased by 10.2% and 4.9%. Under the effect of cyclic reciprocating load, the hysteretic energy is reduced by 15.3%; at the same time, the test curve is fitted by the secondary plastic flow model and the Ramberg–Osgood model and it is found that the shape parameter S
1
and the cyclic strengthening coefficient K' are reduced by 20.1% and 10.2%, While the shape parameter S
2
and the cycle strengthening index n' have no obvious changes.
A simple nanoplatform based on molybdenum disulfide (MoS
2
) nanosheets, a fluorescence quencher (signal off), and a hybridization chain reaction (HCR) signal amplification (signal on) used for the ...enzyme-free, label-free, and low-background signal quantification of microRNA-21 in plasma exosome is reported. According to the sequence of microRNA-21, carboxy-fluorescein (FAM)-labeled hybridization probe 1 (FAM-H1) and hybridization probes 2 (FAM-H2) were designed with excitation maxima at 488 nm and emission maxima at 518 nm. MoS
2
nanosheets could adsorb FAM-H1 and FAM-H2 and quenched their fluorescence signals to reduce the background signal. However, HCR was triggered when microRNA-21 was present. Consequently, HCR products containing a large number of FAM fluorophores can emit a strong fluorescence at 518 nm and could realize the detection of microRNA-21 as low as 6 pmol/L and had a wide linear relation of 0.01–25 nmol/L. This assay has the ability of single-base mismatch recognition and could identify microRNA-21 with high specificity. Most importantly, this approach was successfully applied to the detection of plasma exosomal microRNA-21 in patients with lung cancer, and it is proposed that other targets can also be detected by changing the FAM-H1 and FAM-H2 corresponding to the target sequence. Thus, a novel, hands-on strategy for liquid biopsy was proposed and has a potential application value in the early diagnosis of lung cancer.
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