The combination of transition‐metal catalysis and organocatalysis increasingly offers chemists opportunities to realize diverse unprecedented chemical transformations. By combining iridium with ...chiral thiourea catalysis, direct enantioselective reductive cyanation and phosphonylation of secondary amides have been accomplished for the first time for the synthesis of enantioenriched chiral α‐aminonitriles and α‐aminophosphonates. The protocol is highly efficient and enantioselective, providing a novel route to the synthesis of optically active α‐functionalized amines from the simple, readily available feedstocks. In addition, the reactions are scalable and the thiourea catalyst can be recycled and reused.
The first enantioselective reductive cyanation and phosphonylation of secondary amides have been achieved by the combination of iridium with chiral thiourea catalysis. The protocol is highly efficient and enantioselective, providing a novel route for the synthesis of optically active α‐aminonitriles and α‐aminophosphonates from bench‐stable feedstocks.
The design simulation and fabrication results of a bandpass filter based on micro-electro-mechanical system (MEMS) switches are presented in this paper. The MEMS filter element consists of a MEMS ...capacitance switch and two resonant rings that are fixed onto coplanar waveguide lines through anchor points. The micromachine characteristics of the filter could be optimized to change the center frequency from 8.5 to 12 GHz by improving the geometrical parameters; other electrical parameters of the filter, such as stopband rejection, insertion loss, and return loss at each center frequency, were simulated and calculated. In order to evaluate the MEMS filter design methodology, a filter working at 10.5 GHz fabricated with an aluminum top electrode was used, and it displayed a low insertion loss of 1.12 dB and a high stopband rejection of 28.3 dB. Compared with the simulation results, these proposed filter showed better electrical performance. Our results demonstrated that the filter with the integrated RF MEMS switch not only provides the benefit of reduced size compared with a traditional filter, but also improves stopband rejection, insertion loss, and return loss.
The first organocatalytic asymmetric synthesis of an advanced intermediate of (+)‐sarain A was achieved. This approach featured the employment of an organocatalytic asymmetric Michael addition ...reaction and a nitrogen‐to‐carbon chirality transfer to forge three chiral centers, as well as a catalytic hydrosilylation for the chemoselective reduction of a key lactam intermediate. The tricyclic intermediate contained all the required functionalities for elaborating into (+)‐sarain A.
Get asymmetric: The first organocatalytic asymmetric synthesis of an advanced intermediate of (+)‐sarain A features an organocatalytic asymmetric Michael addition reaction and a nitrogen‐to‐carbon chirality transfer to forge three chiral centers, as well as a catalytic hydrosilylation for the chemoselective reduction of a key lactam intermediate.
Recently, we developed a new strategy for the synthesis of polycyclic structure via a three‐step “2+n” annulation protocol from simple cycloketones and terminal olefinic amides.
Summary of main observation and conclusion
The efficient construction of functionalized polycyclic structures is an important objective in organic synthesis. Herein, we disclose a three‐step “2 + n” ...annulation method for the transformation of cyclic ketones to fused enimines and enones. The method relies on the Suzuki coupling reaction and the amide reductive alkenylation reaction. A series of fused bicyclic (6/6, 6/7, 8/7) and tricyclic (6/6/6; 6/6/7, 6/5/7) ring systems bearing an α,β‐enimine or an α,β‐enone functionality have been synthetized in good overall yields.
An expedient protocol for the efficient assembly of cyclic ketones and ω‐unsaturated amides in a “2 + n” manner to produce fused enimines and enones has been developed.
Objective
To reveal the neuroprotective effect and the underlying mechanisms of a mixture of the main components of
Panax notoginseng
saponins (TSPN) on cerebral ischemia-reperfusion injury and ...oxygen-glucose deprivation/reoxygenation (OGD/R) of cultured cortical neurons.
Methods
The neuroprotective effect of TSPN was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay, flow cytometry and live/dead cell assays. The morphology of dendrites was detected by immunofluorescence. Middle cerebral artery occlusion (MCAO) was developed in rats as a model of cerebral ischemia-reperfusion. The neuroprotective effect of TSPN was evaluated by neurological scoring, tail suspension test, 2,3,5-triphenyltetrazolium chloride (TTC) and Nissl stainings. Western blot analysis, immunohistochemistry and immunofluorescence were used to measure the changes in the Akt/mammalian target of rapamycin (mTOR) signaling pathway.
Results
MTT showed that TSPN (50, 25 and 12.5 µ g/mL) protected cortical neurons after OGD/R treatment (
P
<0.01 or
P
<0.05). Flow cytometry and live/dead cell assays indicated that 25 µ g/mL TSPN decreased neuronal apoptosis (
P
<0.05), and immunofluorescence showed that 25 µ g/mL TSPN restored the dendritic morphology of damaged neurons (
P
<0.05). Moreover, 12.5 µ g/mL TSPN downregulated the expression of Beclin-1, Cleaved-caspase 3 and LC3B-II/LC3B-I, and upregulated the levels of phosphorylated (p)-Akt and p-mTOR (
P
<0.01 or
P
<0.05). In the MCAO model, 50 µ g/mL TSPN improved defective neurological behavior and reduced infarct volume (
P
<0.05). Moreover, the expression of Beclin-1 and LC3B in cerebral ischemic penumbra was downregulated after 50 µ g/mL TSPN treatment, whereas the p-mTOR level was upregulated (
P
<0.05 or
P
<0.01).
Conclusion
TSPN promoted neuronal survival and protected dendrite integrity after OGD/R and had a potential therapeutic effect by alleviating neurological deficits and reversing neuronal loss. TSPN promoted p-mTOR and inhibited Beclin-1 to alleviate ischemic damage, which may be the mechanism that underlies the neuroprotective activity of TSPN.
We disclose that following activation with trifluoromethanesulfonyl anhydride, secondary N-arylamides undergo smooth intermolecular dehydrative 4 + 2 aza-annulation with alkenes under mild conditions ...to give 3,4-dihydroquinolines, amenable to further functionalization. Meanwhile, conditions have been established to allow divergent one pot synthesis of tetrahydroquinolines and quinolines as well as tricyclic analogues from N-arylamides.
•Quantitatively investigated the adsorption and desorption of gas molecules on graphene.•The mechanism for graphene based gaseous sensor working was suggested.•Some methods were suggested to enhance ...the sensitivity and response rate of graphene sensor.
Graphene based gaseous sensor has been shown experimentally to have high potential for detecting gas molecules by measuring the conductance change as induced by the adsorbed molecules on graphene. Currently, there is no atomistic based theoretical model that is able to adequately explain the working of the sensor. Based on a single-atom statistical model, the kinetics of adsorption and desorption of gas molecules on graphene was investigated in the present work, and an atomistic mechanism for the functioning of the sensor is proposed which relies on the change of the conductance when the adsorbed molecules diffuse into the defective sites. This mechanism is in agreement with previous experimental measurements and indicates some possible ways to increase the sensitivity and response speed of the sensor.
The Vaska’s complex—tris(pentafluorophenyl)borane combination was found to be a highly efficient cooperative catalysis system for the hydrosilylative reduction of tertiary amides to yield amines ...under mild conditions. The reaction shows high chemoselectivity, tolerating halide, phenolyl, alkenyl, nitro, nitrile, ester, azido, ketone, and enone functional groups. For unsubstituted cyclohexanone carboxamide, two variations were established to achieve either catalytic concomitant reduction of the two carbonyl groups or selective reduction of the amide carbonyl. The protocol was applied to the efficient synthesis and late-stage modification of several pharmaceuticals and derivatives. Importantly, we showed that by simply prolonging reaction time to 24–28 h, the reaction can reach an exceptionally high efficiency with turnover number (TON) up to 9.8×10
6
and turnover frequency (TOF) up to 408,333 at a quite low catalyst loading of 0.00001 mol% (S/C (Ir) = 10,000,000).
In this paper, two microwave irradiation methods: (i) liquid-phase microwave irradiation (MWI) reduction of graphite oxide suspension dissolved in de-ionized water and N, N-dimethylformamide, ...respectively, and (ii) solid-phase MWI reduction of graphite oxide powder have been successfully carried out to reduce graphite oxide. The reduced graphene oxide products are thoroughly characterized by scanning electron microscopy, atomic force microscopy. X-ray photoelectron spectroscopy, Fourier transform infrared spectral analysis, Raman spectroscopy, UV-Vis absorption spectral analysis, and four-point probe conductivity measurements. The results show that both methods can efficiently remove the oxygen-containing functional groups attached to the graphite layers, though the solid-phase MWI reduction method can obtain far more efficiently a higher quality-reduced graphene oxide with fewer defects. The I(D)/I(G ) ratio of the solid-phase MWI sample is as low as 0.46, which is only half of that of the liquid-phase MWI samples. The electrical conductivity of the reduced graphene oxide by the solid method reaches 747.9 S/m, which is about 25 times higher than that made by the liquid-phase method.
