Photoinduced Metal- and Photosensitizer-Free Decarbonylative C-H Alkylation of Cyclic Sulfamidate Imines.

Photoinduced decarbonylative C-C bond formation with readily accessible aldehydes as alkyl sources is described. This protocol provides a sustainable alternative for the effective construction of diverse valuable 4-alkylated sulfonyl ketimines under metal- and photosensitizer-free conditions. Significantly, in this reaction, air serves as the green oxidant, and cyclic sulfamidate imines play a dual role of substrate and photocatalyst, thus affording a concise reaction system for C-H alkylation of cyclic sulfamidate imines.

Active and stable alcohol dehydrogenase-assembled hydrogels via synergistic bridging of triazoles and metal ions.

Biocatalysis is increasingly replacing traditional methods of manufacturing fine chemicals due to its green, mild, and highly selective nature, but biocatalysts, such as enzymes, are generally costly, fragile, and difficult to recycle. Immobilization provides protection for the enzyme and enables its convenient reuse, which makes immobilized enzymes promising heterogeneous biocatalysts; however, their industrial applications are limited by the low specific activity and poor stability. Herein, we report a feasible strategy utilizing the synergistic bridging of triazoles and metal ions to induce the formation of porous enzyme-assembled hydrogels with increased activity. The catalytic efficiency of the prepared enzyme-assembled hydrogels toward acetophenone reduction is 6.3 times higher than that of the free enzyme, and the reusability is confirmed by the high residual catalytic activity after 12 cycles of use. A near-atomic resolution (2.1 Å) structure of the hydrogel enzyme is successfully analyzed via cryogenic electron microscopy, which indicates a structure-property relationship for the enhanced performance. In addition, the possible mechanism of gel formation is elucidated, revealing the indispensability of triazoles and metal ions, which guides the use of two other enzymes to prepare enzyme-assembled hydrogels capable of good reusability. The described strategy can pave the way for the development of practical catalytic biomaterials and immobilized biocatalysts.

A Biocatalytic Platform for the Synthesis of Enantiopure Propargylic Alcohols and Amines.

Propargylic alcohols and amines are versatile building blocks in organic synthesis. We demonstrate a straightforward enzymatic cascade to synthesize enantiomerically pure propargylic alcohols and amines from readily available racemic starting materials. In the first step, the peroxygenase from Agrocybe aegerita converted the racemic propargylic alcohols into the corresponding ketones, which then were converted into the enantiomerically pure alcohols using the (R)-selective alcohol dehydrogenase from Lactobacillus kefir or the (S)-selective alcohol dehydrogenase from Thermoanaerobacter brokii. Moreover, an enzymatic Mitsunobu-type conversion of the racemic alcohols into enantiomerically enriched propargylic amines using (R)-selective amine transaminase from Aspergillus terreus or (S)-selective amine transaminase from Chromobacterium violaceum was established. The one-pot two-step cascade reaction yielded a broad range of enantioenriched alcohol and amine products in 70-99% yield.

Regio- and enantioselective umpolung gem-difluoroallylation of hydrazones via palladium catalysis enabled by N-heterocyclic carbene ligand.

The enantioselective construction of C-CF2R (R: alkyl or fluoroalkyl) bonds has attracted the attention of synthetic chemists because of the importance of chiral fluorinated compounds in life and materials sciences. Catalytic asymmetric fluoroalkylation has mainly been realized under organocatalysis and Lewis acid catalysis, with substrates limited to carbonyl compounds. Few examples using transition-metal catalysis exist, owing to side reactions including decomposition and isomerization of fluoroalkylating reagents. Herein we report umpolung asymmetric difluoroallylation of hydrazones with 3-bromo-3,3-difluoropropene (BDFP) under palladium catalysis. Difluoroallylation products having quaternary chiral carbon centers are afforded in good yields with high α/γ- and enantioselectivities. The usefulness of the reaction products is demonstrated and an inner-sphere mechanism of the reaction is proposed. The use of chiral N-heterocyclic carbene as ligand is the key for the selectivities as well as the productivity of the reaction.

Visible-Light-Induced Palladium-Catalyzed Selective Defluoroarylation of Trifluoromethylarenes with Arylboronic Acids.

Selective functionalization of inactive C(sp3)-F bonds to prepare medicinally interesting aryldifluoromethylated compounds remains challenging. One promising route is the transition-metal-catalyzed cross-coupling through oxidative addition of the C(sp3)-F bond in trifluoromethylarenes (ArCF3), which are ideal precursors for this process due to their ready availability and low cost. Here, we report an unprecedented excited-state palladium catalysis strategy for selective defluoroarylation of trifluoromethylarenes with arylboronic acids. This visible-light-induced palladium-catalyzed cross-coupling proceeds under mild reaction conditions and allows transformation of a variety of arylboronic acids and ArCF3. Preliminary mechanistic studies reveal that the oxidative addition of the C(sp3)-F bond in ArCF3 to excited-state palladium(0) via a single electron transfer pathway is responsible for the C(sp3)-F bond activation.

Biosynthesis of Chiral Amino Alcohols via an Engineered Amine Dehydrogenase in E. coli.

Chiral amino alcohols are prevalent synthons in pharmaceuticals and synthetic bioactive compounds. The efficient synthesis of chiral amino alcohols using ammonia as the sole amino donor under mild conditions is highly desired and challenging in organic chemistry and biotechnology. Our previous work explored a panel of engineered amine dehydrogenases (AmDHs) derived from amino acid dehydrogenase (AADH), enabling the one-step synthesis of chiral amino alcohols via the asymmetric reductive amination of α-hydroxy ketones. Although the AmDH-directed asymmetric reduction is in a high stereoselective manner, the activity is yet fully excavated. Herein, an engineered AmDH derived from a leucine dehydrogenase from Sporosarcina psychrophila (SpAmDH) was recruited as the starting enzyme, and the combinatorial active-site saturation test/iterative saturation mutagenesis (CAST/ISM) strategy was applied to improve the activity. After three rounds of mutagenesis in an iterative fashion, the best variant wh84 was obtained and proved to be effective in the asymmetric reductive amination of 1-hydroxy-2-butanone with 4-fold improvements in k cat /K m and total turnover number (TTN) values compared to those of the starting enzyme, while maintaining high enantioselectivity (ee >99%) and thermostability (T 50 15 >53°C). In preparative-scale reaction, the conversion of 100 and 200 mM 1-hydroxy-2-butanone catalyzed by wh84 was up to 91-99%. Insights into the source of an enhanced activity were gained by the computational analysis. Our work expands the catalytic repertoire and toolbox of AmDHs.

Stereoselective Functionalization of Racemic Cyclopropylzinc Reagents via Enantiodivergent Relay Coupling.

Efficient construction of optically pure molecules from readily available starting materials in a simple manner is an ongoing goal in asymmetric synthesis. As a straightforward route, transition-metal-catalyzed enantioconvergent coupling between widely available secondary alkyl electrophiles and organometallic nucleophiles has emerged as a powerful strategy to construct chiral center(s). However, the scope of racemic secondary alkylmetallic nucleophiles for this coupling remains limited in specific substrates because of the difficulties in stereoselective formation of the key alkylmetal intermediates. Here, we report an enantiodivergent strategy to efficiently achieve an array of synthetically useful chiral cyclopropanes, including chiral fluoroalkylated cyclopropanes and enantiomerically enriched cyclopropanes with chiral side chains, from racemic cyclopropylzinc reagents. This strategy relies on a one-pot, two-step enantiodivergent relay coupling process of the racemic cis-cyclopropylzinc reagents with two different electrophiles, which involves kinetic resolution of racemic cis-cyclopropylzinc reagents through a nickel-catalyzed enantioselective coupling with alkyl electrophiles, followed by a stereospecific relay coupling of the remaining enantiomeric cyclopropylzinc reagent with various electrophiles, to produce two types of functionalized chiral cyclopropanes with opposite configurations on the cyclopropane ring. These chiral cyclopropanes are versatile synthons for diverse transformations, rendering this strategy effective for obtaining structurally diversified molecules of medicinal interest.

Study of inflammatory factors' effect on the endothelial barrier using piezoelectric biosensor.

This paper used piezoelectric sensor to study the dysfunction of endothelial cell monolayer barrier caused by inflammatory factors. The biocompatible conductive polymer membrane of pPy[pGlu]-pLys was prepared on the surface of the ITO work electrode to improve the interface between the endothelial cell and the electrode. Both the impedance analysis data and the stable plateau stage of sensor's frequency shift indicated that endothelial cells formed a good monolayer barrier on this polymer surface. The response frequency shifts of lipopolysaccharide (LPS)- and histamine-induced endothelial barrier dysfunction were different, which distinguished their different stimulation mechanism. It provided a valuable analysis method for detecting the endothelial barrier function affected by inflammatory factor, and could further promote the application of piezoelectric sensor in cell biology and toxicology research.

Pd-Catalyzed Asymmetric Dearomative Cycloaddition for Construction of Optically Active Pyrroloindoline and Cyclopentaindoline Derivatives: Access to 3a-Aminopyrroloindolines.

Asymmetric dearomative [3 + 2] cycloaddition reactions of 3-nitroindoles with vinyl aziridine and vinyl cyclopropanes have been respectively successfully developed in the presence of a chiral box/Pd(0) complex. A series of enantiomerically enriched 3a-nitro-hexahydropyrrolo[2,3-b]indole and 8b-nitrohexahydrocyclopenta[b]indole derivatives containing three contiguous chiral centers are smoothly obtained in high yields with satisfactory regio-, chemo-, and enantioselectivity. Remarkably, the synthetic utility of this process was demonstrated through direct reductive amination and functionalization of the carbon-carbon double bond of the desired products.

On-Line Monitoring the Growth of E. coli or HeLa Cells Using an Annular Microelectrode Piezoelectric Biosensor.

Biological information is obtained from the interaction between the series detection electrode and the organism or the physical field of biological cultures in the non-mass responsive piezoelectric biosensor. Therefore, electric parameter of the electrode will affect the biosensor signal. The electric field distribution of the microelectrode used in this study was simulated using the COMSOL Multiphysics analytical tool. This process showed that the electric field spatial distribution is affected by the width of the electrode finger or the space between the electrodes. In addition, the characteristic response of the piezoelectric sensor constructed serially with an annular microelectrode was tested and applied for the continuous detection of Escherichia coli culture or HeLa cell culture. Results indicated that the piezoelectric biosensor with an annular microelectrode meets the requirements for the real-time detection of E. coli or HeLa cells in culture. Moreover, this kind of piezoelectric biosensor is more sensitive than the sensor with an interdigital microelectrode. Thus, the piezoelectric biosensor acts as an effective analysis tool for acquiring online cell or microbial culture information.

Construction of Au-IDE/CFP10-ESAT6 aptamer/DNA-AuNPs MSPQC for rapid detection of Mycobacterium tuberculosis.

Au-IDE/CFP10-ESAT6 aptamer/DNA-AuNPs MSPQC for rapid detection of Mycobacterium tuberculosis was constructed based on specific detection of specific fused antigen CFP10-ESAT6 which secreted only by pathogenic M. tuberculosis in its early culture time. CFP10-ESAT6 aptamer was used as sensor specific probe of CFP10-ESAT6 antigen. Au nanoparticles (NPs) was employed to increase sensor senstivity. The Au-IDE/CFP10-ESAT6 aptamer/DNA-AuNPs electrode probe was prepared by modifying of the complementary DNA-AuNPs on to interdigital array microelectrode with CFP10-ESAT6 aptamer. CFP10-ESAT6 aptamer could specifically catch CFP10-ESAT6 protein and formed a tight complex on the electrode surface and resulted in the DNA-AuNPs fragments fell away from the electrode surface. This change can be sensitively detected by IDE-MSPQC sensor. The detection time was 96.3h. Non-pathogenic Mycobacterium did not affect detection. Compared with conventional methods, this approach was specific, more sensitive, and expected to become a valuable analysis tool for the early detection of M. tuberculosis in clinical sample.

Novel S-MSPQC cell sensor for real time monitoring the injury of endothelial cell by LPS and assessing the drug effect on this injury.

A novel square Au microelectrode multi-channel series piezoelectric quartz crystal (S-MSPQC) cell sensor was constructed by square Au microelectrode in series connected with quartz crystal sensor in MSPQC. The experimental results showed square shape Au microelectrode was more sensitive than normally used interdigital microelectrode. New constructed S-MSPQC was successfully used for real time monitoring the injury of human umbilical vein endothelial cells which induced by lipopolysaccharide (LPS) and assessing the drug effects of two anti-oxidative vitamins, VC and VE and their combination against this injury. The detection results showed that the low concentration of LPS may promote the proliferation of the HUVEC cells at first 12h, then it caused the cell apoptosis. The pretreatment of VC or VE on the cells for 12h before adding the LPS could partially reduced the injury of LPS on HUVEC cells. The sensor detection results were all consisted with the results detected by MTT assay and microscopy observation. The synergistic effect of the combination of VC-VE on LPS-induced cell injury was also observed by sensor. Compared with the traditional biological methods, the proposed method is sensitive, label-free, non-invasive, cheap, simple, and automatic. It provides a new automatic tool for cell monitor in the field of cell biology, cytobiology, and drug effects research.

A new aptamer/graphene interdigitated gold electrode piezoelectric sensor for rapid and specific detection of Staphylococcus aureus.

A novel aptamer/graphene interdigitated gold electrode piezoelectric sensor was developed for the rapid and specific detection of Staphylococcus aureus (S. aureus) by employing S. aureus aptamer as a biological recognition element. 4-Mercaptobenzene-diazonium tetrafluoroborate (MBDT) salt was used as a molecular cross-linking agent to chemically bind graphene to interdigital gold electrodes (IDE) that are connected to a series electrode piezoelectric quartz crystal (SPQC). S. aureus aptamers were assembly immobilized onto graphene via the π-π stacking of DNA bases. Due to the specific binding between S. aureus and aptamer, when S. aureus is present, the DNA bases interacted with the aptamer, thereby dropping the aptamer from the surface of the graphene. The electric parameters of the electrode surface was changed and resulted in the change of oscillator frequency of the SPQC. This detection was completed within 60min. The constructed sensor demonstrated a linear relationship between resonance frequency shifts with bacterial concentrations ranging from 4.1×10(1)-4.1×10(5)cfu/mL with a detection limit of 41cfu/mL. The developed strategy can detect S. aureus rapidly and specifically for clinical diagnosis and food testing.

Multichannel series piezoelectric quartz crystal cell sensor for real time and quantitative monitoring of the living cell and assessment of cytotoxicity.

A new multichannel series piezoelectric quartz crystal (MSPQC) cell sensor for real time monitoring of living cells in vitro was reported in this paper. The constructed sensor was used successfully to monitor adhesion, spreading, proliferation, and apoptosis of MG63 osteosarcoma cells and investigate the effects of different concentrations of cobalt chloride on MG63 cells. Quantitative real time and dynamic cell analyses data were conducted using the MSPQC cell sensor. Compared with methods such as fluorescence staining and morphology observation by microscopy, the MSPQC cell sensor is noninvasive, label free, simple, cheap, and capable of online monitoring. It can automatically record the growth status of cells and quantitatively evaluate cell proliferation and the apoptotic response to drugs. It will be a valuable detection and analysis tool for the acquisition of cellular level information and is anticipated to have application in the field of cell biology research or cytotoxicity testing in the future.