Latest ArticlesA catalytic asymmetric total synthesis of (+)-vincamine is presented. Key features of the synthesis include a Pd-catalyzed enantioselective decarboxylative allylation to form the C20 quaternary stereogenic center and a stereoselective iminium reduction to install the critical cis-C20/C21 relative stereochemisty.
The Cu(I)-catalyzed [4 + 1] annulation of vinyl indoles and a carbene precursor is a powerful method for constructing cyclopentaindole derivatives. Density functional theory (DFT) calculations were used to elucidate the mechanism and regioselectivity of this reaction. After Cu-assisted indole C3-alkylation, direct 1,5-annulation was favored over the Cu-assisted annulation pathway. Furthermore, the regioselectivity for 1,5-annulation was attributed to the generated five-membered-ring product being more stable than the three-membered-ring product from 1,3-annulation, which was the kinetically favored pathway.
Both sulfur and fluorine play important roles in organic synthesis, the life science, and materials science. The direct incorporation of these elements into organic scaffolds with precise control of the oxidation states of sulfur moieties is of great significance. Herein, we report the highly selective electrochemical vicinal fluorosulfenylation and fluorosulfoxidation reactions of alkenes, which were enabled by the unique ability of electrochemistry to dial in the potentials on demand. Preliminary mechanistic investigations revealed that the fluorosulfenylation reaction proceeded through a radical-polar crossover mechanism involving a key episulfonium ion intermediate. Subsequent electrochemical oxidation of fluorosulfides to fluorosulfoxides were readily achieved under a higher applied potential with the adventitious H2O in the reaction mixture.
Dimeric sesquiterpenoids possessing densely substituted 7-norbornenone/7-norbornenol motifs pose a considerable challenge for chemical synthesis. From a strategic perspective, one could envision intermolecular Diels−Alder cycloaddition as a straightforward method for assembling alkyl-substituted 7-norbornenones. However, this approach is hindered by lability of the required dienes, namely alkyl-substituted cyclopentadienones. Here we report a one-pot protocol for construction of alkyl-substituted 7-norbornenones from electron-deficient olefins and a cyclopentenone derivative. DDQ was found to be an effective oxidant for generating a cyclopentadienone intermediate in situ from the enone. A series of sterically congested 7-norbornenone-containing polycyclic compounds were prepared by using this protocol.
Noble metal aerogels (NMAs), belonging to the porous material, have exhibited excellent catalytic performance. Although the synthesis method continues to improve, it still exists some problems which hindered the experimental process, such as high concentration of noble metal precursors, long synthesis cycle, expensive production cost, and uncontrollable ligament length. In this work, ultrasonic wave and reducing agent NaBH4 were simultaneously applied to gelation process. With the cavitation of ultrasound, it can generate huge energy with heating and stirring, thus gelation reaction proceeded quickly, and even completed the process in only a few seconds, that is much faster than the recorded. A wide concentration range was successfully expanded from 0.02 mmol/L to 62.5 mmol/L. Further, we extended this method to a variety of noble metal elements (Au, Ru, Rh, Ag, Pt, Pd), and this method is adaptive for the synthesis of single metal aerogels (Au, Ag, Ru, Rh, Pd), bimetal and trimetal aerogels (Au-Ag, Au-Rh, Au-Ru, Au-Pt, Au-Pd, Au-Pt-Pd). In addition, the ligament size of alloy aerogels are 10 nm or less. Moreover, their brilliant properties were demonstrated in hydrogen evolution reaction (HER) and ethanol oxidation reaction (EOR).
Metal-organic frameworks (MOFs) as a type of crystalline heterogeneous catalysts have shown potential application in photocatalytic CO2 reduction. However, MOF catalysts with high efficiency and selectivity are still in pursuit. Herein, by a bimetallic strategy, the catalytic performance of a Co-MOF for photocatalytic CO2 reduction was enhanced. Specifically, the Co-MOF based on 4, 5-dicarboxylic acid (H3IDC) and 4, 4ʹ-bipydine (4, 4ʹ-bpy) can catalyze CO2 reduction to CO, with high efficiency but relatively low selectivity. After replacement of 2/3 Co(Ⅱ) with Ni(Ⅱ) within Co-MOF, the resulted isostructural Co1Ni2-MOF not only retains high efficiency for photocatalytic CO2 reduction, but also shows enhanced CO selectivity. The CO evolution rate reaches 1160 µmol g−1 h−1 and the CO selectivity reaches as high as 94.6%. The enhanced photocatalytic CO2 reduction performance is supported by theoretical calculation results. This case demonstrates that bimetallic strategy is an effective mean to optimize the catalytic performance of MOF catalysts for photochemical CO2 reduction.
Application of matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) to investigate the spatiotemporal alterations of lipids in biological tissues has brought many significant results. However, the presence of structural isomers varying in C=C double bond (DB) locations makes isomer-resolved MSI an urgent need. Herein, we introduce a new type of light-driven on-tissue [2 + 2] cycloaddition reaction coupled with MALDI-MS/MS imaging to identify lipid DB position isomers and their spatial signatures in biological tissues. 3-Benzoylpyridine was introduced as a novel derivatization reagent, and it exhibited great reactivity toward lipid C=C bond to form oxetanes under both ultraviolet light and visible light irradiation. With this approach, DB position isomers of lipids were imaged with highly differential levels in distinct regions of rat brain, providing an accurate and spatially resolved approach to study tissue lipidomics.
Colorectal cancer (CRC) is still the leading cause of cancer death worldwide, but the clinical effect of drug therapy such as irinotecan is not an ideal way at present. In recent years, probiotics have attracted much attention, and the combination of probiotics may play an important role in the prevention and treatment of CRC. This work proposed a cellular chip-MS system, to study the synergistic effects of probiotic Lactobacillus rhamnosus GG (L.GG) and irinotecan on HCT116 cells by cell viability and on-line mass spectrometry (MS) analysis. The double-layer chip sandwiched with a polycarbonate membrane can co-culture HCT116 cells and L.GG. And the solid phase microextraction chip can be used for desalination and concentration. Finally, the extracted chemicals were entered the electrospray ionization quadrupole time-of-flight MS to detect irinotecan metabolites. The results showed that with the increasing concentration of co-cultured L.GG, the percentage of living HCT116 cells decreased, but the relative amount of metabolized SN-38 by HCT116 cells increased. Therefore, the microfluidic system can be used to detect and monitor the synergistic effect of irinotecan-L.GG combination on HCT116 cells. In summary, our study provided experimental evidence for the first time with potential applications of irinotecan-L.GG combination in CRC treatment, and the cellular chip-MS system as a powerful tool can be used in the experiments of probiotics as new drugs.
Due to the involvement of four-electron transfer process at photoanode, water oxidation is the rate-limiting step in water splitting reaction. To settle this dilemma, ZnCo2O4 nanoparticles are combined with BiVO4 to form a p-n ZnCo2O4/BiVO4 heterojunction photoanode, which is proved by an input voltage−output current test. The built-in electric field formed within the heterojunction structure promotes the effective separation of electrons and holes. ZnCo2O4 is also an effective water oxidation cocatalyst, since it could cause the holes entering the electrode/electrolyte interface rapidly for the subsequent water oxidation reaction. The photocurrent density of ZnCo2O4/BiVO4 composite photoanode reaches 3.0 mA/cm2 at 1.23 V vs. RHE in 0.5 mol/L sodium sulfate under AM 1.5G simulated sunlight, about 2.1 times greater than that of BiVO4 (1.4 mA/cm2). These results suggest the potential of ZnCo2O4 nanoparticles for improving photoelectrochemical water splitting anode materials.
Although peroxidase-like nanozymes have made great progress in bioanalysis, few current nanozyme-based biosensors are constructed for discriminating isomers of organic compounds. Herein, fluorescent metal-organic framework (MOF)-based nanozyme is utilized for phenylenediamine isomers discrimination and detection. NH2-MIL-101(Fe), as a member of Fe-based MOFs, functions as not only fluorescent indicator but also peroxidase mimics. In the presence of H2O2, NH2-MIL-101(Fe) can catalyze the oxidation of o-phenylenediamine (OPD) and p-phenylenediamine (PPD) into their corresponding oxidation products (OPDox and PPDox), which in turn quench its intrinsic fluorescence at 445 nm via inner filter effect (IFE). Differently, a new fluorescence peak at 574 nm is observed for OPDox. Thus, a ratiometric fluorescence method for the detection of OPD can be designed with the fluorescence intensity ratio F574/F445 as readout. This proposed strategy displays excellent discrimination ability for three phenylenediamines and may open new applications of MOFs in environmental science.
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