C‐aryl glycosides are popular basic skeletons in biochemistry and pharmaceutical chemistry. Herein, ruthenium‐catalyzed highly stereo‐ and site‐selective ortho‐ and meta‐CAr−H glycosylation is ...described. A series of C‐aryl pyranosides and furanosides were synthesized by this method. The strategy showed good substrate scope, and various N‐heterocyclic directing groups were compatible with the reaction system. A mechanistic study suggested that the key pathway of ortho‐CAr−H glycosylation might involve oxidative addition/reduction elimination, whereas aryl meta‐C−H glycosylation was mediated by σ‐activation. Density functional theory calculations also showed that the high stereoselectivity of meta‐CAr−H glycosylation was due to steric hindrance.
A series of C‐aryl pyranosides and furanosides were synthesized by ruthenium‐catalyzed ortho‐ and meta‐CAr−H glycosylation. Mechanistic studies suggest that the key pathway of ortho‐CAr−H glycosylation involves an oxidative addition/reductive elimination process, while aryl meta‐C−H glycosylation is mediated by σ‐activation. DFT calculations showed that steric hindrance is responsible for the high stereoselectivity of meta‐CAr−H glycosylation.
The aryl‐to‐vinyl nickel 1,4‐migration (1,4‐Ni migration) reaction has been reported for the first time. The generated alkenyl Ni species undergo a reductive coupling reaction with unactivated ...brominated alkanes affording a series of trisubstituted olefins. This tandem reaction exhibits mild conditions, a broad substrate scope, high regioselectivity, and excellent Z/E stereoselectivity. A series of controlled experiments have shown that the critical 1,4‐Ni migration process is reversible. In addition, the alkenyl nickel intermediates obtained after migration are highly Z/E stereoselective and do not undergo Z/E isomerization. The obtained trace isomerization products are caused by the instability of the product.
The 1,4‐nickel migration process from aryl to alkenyl groups is now reported for the first time. The alkenyl nickel intermediates generated by this highly stereoselective migration process can be coupled with brominated alkanes to form multisubstituted olefins. The current method provides a new and efficient approach for the synthesis of Z/E olefins with high stereoselectivity.
Controllable chemoselectivity and regioselectivity synthesis of 3‐sulfinylated, 3‐sulfenylated and 2‐sulfonylated indoles via direct C−H functionalization are realized under metal‐free conditions. In ...particular, the synthesis of 3‐arylsulfinylindoles in high yields from a sulfone substrate in water without additives is reported. The process displays excellent functional groups compatibility. p‐Toluenesulfonyl cyanide (TsCN) possesses a hexavalent sulfonyl group, as an odorless and easy‐to‐handle solid, which has been used as a new sulfur reagent through the cleavage of S−C and S=O bonds in our work.
We designed and synthesized iron doped CuSn(OH)6 (Fe/CuSn(OH)6) microspheres, which was selected as a nanoenzyme to detect hydrogen peroxide (H2O2), by a coprecipitation method for the first time. ...Significantly, Fe/CuSn(OH)6 microspheres revealed the high peroxidase-like activity, which was evaluated using the peroxidase substrate 3,3′,5,5′-tetramethylbenzidine (TMB) catalytically oxidized by H2O2. Colorless TMB could be turned into oxidized TMB (oxTMB) with a blue color change in the process of oxidation. The catalytic reaction mechanism has been proved to be •OH, attributing to H2O2 decomposition. On the basis of the high peroxidase mimetic activity of Fe/CuSn(OH)6 microspheres, a novel, simple, and sensitive H2O2 colorimetric detection system was successfully constructed. Experimental data revealed that the Fe/CuSn(OH)6 microspheres nanoenzyme additionally demonstrated the high peroxidase-like activity compared with horseradish peroxidase. Furthermore, based on the Fe/CuSn(OH)6, a rapid detection of H2O2 could be come true in the wide range (30–1000 μM) with a lower detection limit of 9.49 μM (S/N = 3). The feasibility of this convenient method was confirmed by qualitative detection of H2O2 residue in milk.
C-oligosaccharides are found in natural products and drug molecules. Despite the considerable progress made during the last decades, modular and stereoselective synthesis of C-oligosaccharides ...continues to be challenging and underdeveloped compared to the synthesis technology of O-oligosaccharides. Herein, we design a distinct strategy for the stereoselective and efficient synthesis of C-oligosaccharides via palladium-catalyzed nondirected C1-H glycosylation/C2-alkenylation, cyanation, and alkynylation of 2-iodoglycals with glycosyl chloride donors while realizing the difunctionalization of 2-iodoglycals. The catalysis approach tolerates various functional groups, including derivatives of marketed drugs and natural products. Notably, the obtained C-oligosaccharides can be further transformed into various C-glycosides while fully conserving the stereochemistry. The results of density functional theory (DFT) calculations support oxidative addition mechanism of alkenyl-norbornyl-palladacycle (ANP) intermediate with α-mannofuranose chloride and the high stereoselectivity of glycosylation is due to steric hindrance.
This manuscript describes an unusual Pd-catalyzed rearrangement reaction. It provides efficient access to 1-phenanthrol derivatives using allyloxy-tethered aryl iodides. This rearrangement process ...involves the cleavage of a C-I bond, a C-O bond and C-H bonds, and the formation of two C-C bonds in one-pot. It is likely that the key to the success of this rearrangement is
β-carbon elimination from a strained palladacycle.
Multicomponent reactions can efficiently construct complex molecular structures from simple precursors. Herein, a novel ruthenium-catalyzed three-component highly selective remote C-H ...functionalization of 8-aminoquinoline amides has been described. The reaction tolerates a wide range of functional groups, producing arylation/difluoroalkylation products of olefins with potential biological activity and pharmaceutical value. Radical scavenging and radical clock experiments show that a free radical process is involved and a H/D exchange experiment suggests that the reaction might involve
ortho
-C-H activation of the aromatic ring. A possible mechanism is proposed.
Multicomponent reactions can efficiently construct complex molecular structures from simple precursors.
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•Paper-based electrochemical immunosensor for carcinoembryonic antigen is developed.•Novel flower-like gold modified paper electrode is used as sensor platform.•Gold-silver bimetallic ...nanoparticles are used as signal amplification label.
An enzyme-free electrochemical immunoassay is introduced into microfluidic paper-based analytical devices for the first time using novel three dimensional flower-like Au nanoparticles modified paper working electrode (FLAuNPs-PWE) as sensor platform and gold (Au)-silver (Ag) bimetallic nanoparticles (Au-Ag BMNPs) as tracer. FLAuNPs with large surface area serve as an effective matrix for primary antibodies. Au-Ag BMNPs with good biological activity, such as mimicking natural peroxidases, are used for binding of signal antibodies (Ab2). Then the Ab2 labeled BMNPs is linked to the FLAuNPs-PWE via sandwich immunoreactions. Enhanced sensitivity is achieved by efficient catalysis of the Au-Ag BMNPs toward hydrogen peroxide. Under the optimized experimental conditions, the proposed paper-based electrochemical immunosensor exhibits excellent analytical performance for enzyme-free detection of carcinoembryonic antigen, ranging from 0.001-50ngmL−1 with a low detection limit of 0.3pgmL−1. The immunosensor shows good precision, acceptable stability and reproducibility. The proposed method provides a new promising platform for the design of the highly sensitive detection method, showing great promise for clinical application.
Based on subsurface mooring observations and HYCOM data, a complete investigation was conducted of the near-inertial waves (NIWs) caused by Typhoon MITAG to the east of Taiwan. HYCOM data were mainly ...used to reveal the role played by anticyclonic eddies in the propagation of NIWs. The results show that most typhoon-generated NIWs propagate towards negative vorticity, and NIWs near the edge gradually accumulated towards the eddy center and down to 800 m. NIWs propagating through the thermocline to the deep ocean were mainly concentrated in the eddy, and the near-inertial energy flux showed a significant enhancement from 400 to 600 m. Moreover, the downwards propagation of NIWs in the eddy enhanced the kinetic energy of background flow. NIWs outside the anticyclonic eddy dissipated quickly, while inside the eddy, there were high value areas of e-folding time. Dynamic mode decomposition illustrates that the anticyclonic eddy mainly captures higher modes of NIWs, and the state of continuous energy growth of higher modes can be maintained for more than a week. In addition, NIWs can also be carried westwards by the advection of the mean background flow at the eddy’s edge.
Due to the unique physical processes of mesoscale eddies, the physical and biogeochemical properties within the subsurface anticyclonic eddy (SSAE) and in the surrounding water are distinct. Analyses ...using satellite and model data have revealed distinct seasonal variations in the central potential density structure of a long-standing SSAE south of Japan; this SSAE exhibits a normal concave isopycnals structure from January to April and a convex lens isopycnals structure from May to December, and these variations may be related to the subduction of low-potential vorticity (PV) mode water. In contrast to the idea of the self-sustained oscillation mechanism, the strength of the SSAE was enhanced due to the eddy kinetic energy provided by dramatic increasing of the positive baroclinic conversion rate during the Kuroshio path transition period from the non-large meander (NLM) path to the large meander (LM) path. Twofold to threefold enhancement of chlorophyll (CHL) was detected in the subsurface CHL maximum layers at the core of the SSAE, and this enhancement was related to the injection of nutrients into the euphotic layer due to winter mixing and the convex of isopycnals. During the period from May to December, elevated CHL and dissolved oxygen (DO) levels and reduced nitrate levels were observed along the periphery of the eddy below the maximum subsurface CHL anomaly depth. The combined result of these two processes: (1) the central downward displaced isopycnals caused by intensified SSAE, and (2) winter mixing deepened to the nutricline due to the thickened mixed layer depth (MLD) and weakened stratification in winter 2017 (during the NLM period) may have led to numerous nutrients and CHL enrichments throughout the mixed layer, thus generating a CHL bloom in the following April. The SSAE intensified in winter 2018 (during the LM period), whereas the shallower MLD and stronger stratification limited the depth of CHL downward displacement.
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