Electrochemical ring-opening carboxylation of cyclic carbonate with carbon dioxide.

Electroreductive ring-opening carboxylation of styrene carbonates with CO2 to achieve dicarboxylic acids and/or ß-hydroxy acids has been developed via the selective cleavage of the C(sp3)-O bond in cyclic carbonates. The product selectivity is probably determined by the stability and reactivity of the key benzylic radical and carbanion intermediate.

Electroreductive Ring-Opening Carboxylation of 1,3-Oxazolidin-2-ones with CO2 for Accessing ß-Amino Acids.

Electrocarboxylation of the C(sp3)-O bond in 1,3-oxazolidin-2-ones with CO2 to achieve ß-amino acids is developed. The C-O bond in substrates can be selectively cleaved via the single electron transfer on the surface of a cathode or through a CO2• - intermediate under additive-free conditions. A great diversity of ß-amino acids can be obtained in a moderate to excellent yield and readily converted to various biologically active compounds.

Eletrocarboxylation Reactions Using CO2 Both as Promoter and Carboxylative Reagent.

Electrocarboxylation reaction, which employs organic electrosynthesis to achieve the utilization of CO2 as a carboxylative reagent, provides a powerful and efficient tool for the preparation of organic carboxylic acid. In some electrocarboxylation reactions, CO2 also acts as a promoter to facilitate the desired reaction. This concept mainly highlights recent CO2 -promoted electrocarboxylation reactions via CO2 ⋅- intermediate or transiently protective carboxylation of active intermediate with CO2 .

Electroreductive Ring-Opening Carboxylation of Cycloketone Oxime Esters with Carbon Dioxide.

Electroreductive ring-opening carboxylation of cycloketone oxime esters with atmospheric carbon dioxide is reported. This reaction proceeded under simple constant current conditions in an undivided cell using glassy carbon as the cathode and magnesium as the sacrificial anode, providing substituted γ- and δ-cyanocarboxylic acids in moderate to good yields. Electrochemically generated cyanoalkyl radicals and cyanoalkyl anion are proposed as the key intermediates.

Direct and Selective Electrocarboxylation of Styrene Oxides with CO2 for Accessing ß-Hydroxy Acids.

Highly selective and direct electroreductive ring-opening carboxylation of epoxides with CO2 in an undivided cell is reported. This reaction shows broad substrate scopes within styrene oxides under mild conditions, providing practical and scalable access to important synthetic intermediate ß-hydroxy acids. Mechanistic studies show that CO2 functions not only as a carboxylative reagent in this reaction but also as a promoter to enable efficient and chemoselective transformation of epoxides under additive-free electrochemical conditions. Cathodically generated α-radical and α-carbanion intermediates lead to the regioselective formation of α-carboxylation products.

Electrocarboxylation of N-Acylimines with Carbon Dioxide: Access to Substituted α-Amino Acids.

Direct electrocarboxylation of various N-acylimines with atmospheric CO2 is achieved in an undivided cell under mild conditions, affording substituted α-amino acids in yields of 62-95%. This reaction is conducted with high efficiency using triethanolamine as an external reductant under nonsacrificial anode conditions, and can be facilely performed on gram scale. Preliminary mechanistic studies including cyclic voltammetry and control experiments support N-radical carbanion as the key intermediate.

Analysis of stability of reference genes for qPCR in bovine preadipocytes during proliferation and differentiation in vitro.

The stability of internal reference genes is crucial to the reliability of gene expression results using real-time fluorescence quantitative PCR (qRT-PCR). Inappropriate reference genes may lead to inaccurate results or even wrong conclusions. This study aims to identify stable reference genes for analyzing the expression of proliferation-related and differentiation-inducing genes in bovine primary preadipocytes (BPPs) in vitro. In this study, the stability of 16 candidate internal reference genes (GAPDH, ACTB, PPIA, LRP10, HPRT1, YWHAZ, B2M, TBP, EIF3K, RPS9, UXT, 18S rRNA, RPLP0, MARVELD, EMD and RPS15A) for qRT-PCR at proliferation and differentiation stages of BPPs was investigated by three different algorithms (geNorm, NormFinder and BestKeeper). The expression of two marker genes, PCNA and LPL, was used to determine the validity of the candidate reference genes (RGs) at the proliferation and differentiation stages, respectively. The results showed that GAPDH and RPS15A were the most stable RGs in the proliferation of bovine primary preadipocyte, while PPIA was the least stable internal reference gene. RPLP0 and EIF3K were the most stable RGs in the differentiation induction of bovine primary preadipocyte, while GAPDH was the least stable internal reference gene. This study of RGs laid the foundation for subsequent research into the mechanism of proliferation and differentiation of BPPs in vitro using qRT-PCR.

Screening and validation of reference genes for qRT-PCR of bovine skeletal muscle-derived satellite cells.

The accuracy of sixteen commonly used internal reference genes was assessed in skeletal muscle-derived satellite cells of Qinchuan cattle at different stages of proliferation and induction of differentiation to determine the most suitable ones. Quantitative real-time PCR and three commonly used algorithmic programs, GeNorm, NormFinder and BestKeeper, were used to evaluate the stability of expression of the candidate internal reference genes (GAPDH, ACTB, PPIA, LRP10, HPRT1, YWHAZ, B2M, TBP, EIF3K , RPS9, UXT, 18S rRNA, RPLP0, MARVELD, EMD and RPS15A) in skeletal muscle-derived satellite cells at 0, 12, 24, 36 and 48 h of growth and after differentiation for 0, 2, 4, 6 and 8 days. The expression of two satellite cell marker genes, CCNA2 and MYF5, was used for validation analysis. The results of the software analyses showed that GAPDH and RPS15A were the most stable reference gene combinations during in vitro proliferation of bovine skeletal muscle-derived satellite cells, RPS15A and RPS9 were the most stable reference gene combinations during in vitro induction of differentiation of the cells, and PPIA was the least stable reference gene during proliferation and differentiation and was not recommended. This study lays the foundation for the selection of reference genes for qRT-PCR during the proliferation and induction of differentiation of bovine skeletal muscle-derived satellite cells.

Carboxylative Cyclization of 2-Butenoates with Carbon Dioxide: Access to Glutaconic Anhydrides.

Cyclic anhydrides are versatile synthons and functional comonomers. Herein, we reported an organic base-promoted carboxylative cyclization of 2-butenoates with carbon dioxide to produce important glutaconic anhydrides in good yields. This metal-free reaction showed broad substrate scopes and proceeded under mild reaction conditions.

Transcriptional regulation of bovine elongation of very long chain fatty acids protein 6 in lipid metabolism and adipocyte proliferation.

The elongation of very long chain fatty acids protein 6 (ELOVL6) gene encodes a key enzyme that plays a role in lipogenesis through the catalytic elongation of both saturated and monounsaturated fatty acids. Previous studies have described the high expression of bovine ELOVL6 in adipose tissues. However, transcriptional regulation and the functional role of ELOVL6 in lipid metabolism and adipocyte proliferation remain unexplored. Here, a 1.5 kb fragment of the 5'-untranslated region promoter region of ELOVL6 was amplified from the genomic DNA of Qinchuan cattle and sequenced. The core promoter region was identified through unidirectional 5'-end deletion of the promoter plasmid vector. In silico analysis predicted important transcription factors that were then validated through site-directed mutation and small interfering RNA interference with an electrophoretic mobility shift assay. We found that the binding of KLF6 and PU.1 transcription factors occurred in the region -168/+69. Both perform a vital regulatory function in the transcription of bovine ELOVL6. Overexpression of ELOVL6 significantly upregulated the expression of peroxisome proliferator activated receptor γ (PPARγ), but inhibited the expression of fatty acid-binding protein 4 (FABP4), while silencing of ELOVL6 negatively regulated the messenger RNA expression level of PPARγ, FABP4, ACSL, and FATP1. In addition, ELOVL6 promotes adipocyte proliferation by regulating the cell-cycle genes' expression. Taken together, these findings provide useful information about the transcriptional regulation and functional mechanisms of bovine ELOVL6 in lipid metabolism and adipocyte proliferation in Qinchuan cattle.

[Temporal expression of PD-1 and PD-L1 during the development of experimental periodontitis in rats and its implications].

PURPOSE: To study the temporal expression of programmed death receptor 1 (PD-1) and its ligand (PD-L1) in the development of periodontitis in rats. METHODS: SD rats were randomly divided into control group and model group, and 4 subgroups were divided in each model group according to the time of measurement: group A (1 week), group B (2 weeks), group C (3 weeks) and group D (4 weeks). There were 8 rats in each subgroup. Maxillary periodontitis models were made by using "thread ligation + vaccination LPS-PG" in rats. Periodontal tissue specimens were examined and bone resorption areas were determined in each group. Tumor necrosis factor alpha (TNF-α), interleukin-1 (IL-1ß), interleukin 6 (IL-6) and transforming growth factor beta (TGF-ß) mRNA in periodontal tissue in each group were determined by RT-PCR method. PD-1 and PD-L1 protein expression in periodontal tissues in each group were determined by Western blotting. The data were analyzed by SPSS 22.0 software package. RESULTS: During modeling period, amelocemental junction-alveolar crest(ACJ-AC) distance and bone resorption area of the first molar in model group gradually increased (P<0.05), which were significantly different from the control group at the corresponding time point (P<0.01). During modeling period, TNF-α, IL-1ß and IL-6 mRNA level in periodontal tissues in the model group was continuously increased(P<0.05), and TGF-ß mRNA was continuously decreased(P<0.05), which was significantly different from the control group at the corresponding time point(P<0.01). During disease progress, PD-1 and PD-L1 protein level in periodontal tissues in each model group was continuously increased(P<0.05), which was significantly different from the control group at the corresponding time point (P<0.01); and PD-1 and PD-L1 protein levels in periodontal tissues in each model group was positively correlated to TNF-α and IL-6 mRNA levels(P<0.01). CONCLUSIONS: PD-1, as an immunosuppressive molecule and its receptor PD-L1, can promote the progression of periodontal inflammation, and its effect may be achieved by regulating the expression of TNF-α and IL-6.Regulating the expression of PD-1 and PD-L1 may be a new target for the treatment of periodontitis.

High Thermoelectric Figure of Merit Achieved in Cu2S1- xTe x Alloys Synthesized by Mechanical Alloying and Spark Plasma Sintering.

Chalcogenides have been considered as promising thermoelectric materials because of their low cost, nontoxicity, and environmental benignity. In this work, we synthesized a series of Cu2S1- xTe x (0 ≤ x ≤ 1) alloys by a facile, rapid method of mechanical alloying combined with spark plasma sintering process. The Cu2S1- xTe x system provides an excellent vision of the competition between pure phase and phase transformation, entropy-driven solid solution, and enthalpy-driven phase separation. When the Te concentration increases, the Cu2S1- xTe x system changed from the pure monoclinic Cu2S at x = 0 to monoclinic Cu2S1- xTe x solid solution at 0.02 ≤ x ≤ 0.06 and then transforms to hexagonal Cu2S1- xTe x solid solution at 0.08 ≤ x ≤ 0.1. The phase separation of hexagonal Cu2Te in the hexagonal Cu2S matrix occurs at 0.3 ≤ x ≤ 0.7 and finally forms the hexagonal Cu2Te at x = 1. Owing to the changed band structure and the coexisted Cu2S and Cu2Te phases, greatly enhanced power factor was achieved in all Cu2S1- xTe x (0 < x < 1) alloys. Meanwhile, the point defect introduced by the substitution of Te/S atoms strengthened the phonon scattering, resulting in a lowered lattice thermal conductivity in most of these solid solutions. As a consequence, Cu2S0.94Te0.06 exhibits a maximum ZT value of 1.18 at 723 K, which is about 3.7 and 14.8 times as compared to the values of pristine Cu2S (0.32) and Cu2Te (0.08), respectively.

1,3-Dipolar Cycloaddition of Nitrile Imine with Carbon Dioxide: Access to 1,3,4-Oxadiazole-2(3H)-ones.

Efficient synthesis of 1,3,4-oxadiazole-2(3H)-one was achieved by CsF/18-crown-6 mediated 1,3-dipolar cycloaddition of nitrile imine and 2.0 MPa of CO2. CsF/18-crown-6 played a key role in enhancing the reactivity of CO2 as a 1,3-dipolarophile. The practical utility of this transition-metal-free approach to 1,3,4-oxadiazole-2(3H)-one is highlighted by the convenient synthesis of a commercial herbicide Oxadiazon and a MAO B inhibitor.

Access to α-Arylglycines by Umpolung Carboxylation of Aromatic Imines with Carbon Dioxide.

A straightforward and transition-metal-free approach for the efficient synthesis of α-arylglycine derivatives from aromatic imines and carbon dioxide was enabled by an umpolung carboxylation reaction. Various substituted diphenylmethimines underwent the carboxylation smoothly with carbon dioxide in the presence of potassium tert-butoxide and 18-crown-6 to give the corresponding carboxylated products in good to high yields. Besides the enhancement of the solubility of potassium tert-butoxide in THF, 18-crown-6 also plays key roles in suppressing the reverse protonation or 1, 3-proton shift isomerization as well as by stabilizing the carboxylated intermediate.

CO2-Mediated Formation of Chiral Carbamates from meso-Epoxides via Polycarbonate Intermediates.

Carbon dioxide has attracted broad interest as a renewable C1 feedstock for efficient transformation into value-added organic chemicals; nevertheless, far less attention was paid to its stereochemically controlled catalytic fixation/conversion processes. Here, we report a new strategy for the selective synthesis of chiral carbamates from carbon dioxide via polycarbonate intermediates, which are formed by the desymmetric copolymerization of meso-epoxides using enantiopure dinuclear Co(III) catalyst systems with 99% enantioselectivity. Subsequent degradation reaction of the resultant polycarbonates with various primary or secondary amine nucleophiles can afford optically active carbamates, with the complete configuration retention of the two chiral carbon centers. Our accomplishment reported here opens up a new route to prepare a wide range of CO2-based carbamate scaffolds with excellent yields and 99% enantiomeric excess.

DBU-promoted carboxylative cyclization of o-hydroxy- and o-acetamidoacetophenone.

The carboxylative cyclization of o-hydroxy- and o-acetamidoacetophenone with carbon dioxide promoted by the organic base 1,8-diazabicycloundec-7-ene (DBU) is reported. This reaction provides convenient access to the biologically important compounds 4-hydroxy-2H-chromen-2-one and 4-hydroxy-2(1H)-quinolinone in moderate to good yields using carbon dioxide as the carboxylation reagent. An acyl migration from nitrogen to carbon is observed in the reaction of o-acetamidoacetophenone.

Synthesis of oxazolidine-2,4-diones by a tandem phosphorus-mediated carboxylative condensation-cyclization reaction using atmospheric carbon dioxide.

The oxazolidine-2,4-dione motif is found frequently in biologically important compounds. A tandem phosphorus-mediated carboxylative condensation of primary amines and α-ketoesters/base-catalyzed cyclization reaction have been developed. These processes provide a novel and convenient access to various oxazolidine-2,4-diones in a one-pot fashion using atmospheric carbon dioxide and readily available substrates under very mild and transition-metal-free conditions.

Enantioselective rhodium-catalyzed isomerization of 4-iminocrotonates: asymmetric synthesis of a unique chiral synthon.

An enantioselective isomerization of 4-iminocrotonates catalyzed by a rhodium(I)/phosphoramidite complex is described. This reaction uses widely available amines to couple with 4-oxocrotonate to provide a convenient access to a central chiral building block in good yield and high enantioselectivity. Although the mechanism of this new transformation remains unclear, both Rh and the phosphoramidite play a central role.

Fast CO2 sequestration, activation, and catalytic transformation using N-heterocyclic olefins.

N-Heterocyclic Olefin (NHO) with high electronegativity at the terminal carbon atom was found to show a strong tendency for CO2 sequestration, affording a CO2 adduct (NHO-CO2). X-ray single crystal analysis revealed the bent geometry of the binding CO2 in the NHO-CO2 adducts with an O-C-O angle of 127.7-129.9°, dependent on the substitute groups of N-heterocyclic ring. The length of the C(carboxylate)-C(NHO) bond is in the range of 1.55-1.57 Å, significantly longer than that of the C(carboxylate)-C(NHC) bond (1.52-1.53 Å) of the previously reported NHC-CO2 adducts. The FTIR study by monitoring the ν(CO2) region of transmittance change demonstrated that the decarboxylation of NHO-CO2 adducts is easier than that of the corresponding NHC-CO2 adducts. Notably, the NHO-CO2 adducts were found to be highly active in catalyzing the carboxylative cyclization of CO2 and propargylic alcohols at mild conditions (even at ambient temperature and 0.1 MPa CO2 pressure), selectively giving α-alkylidene cyclic carbonates in good yields. The catalytic activity is about 10-200 times that of the corresponding NHC-CO2 adducts at the same conditions. Two reaction paths regarding the hydrogen at the alkenyl position of cyclic carbonates coming from substrate (path A) or both substrate and catalyst (path B) were proposed on the basis of deuterium labeling experiments. The high activity of NHO-CO2 adduct was tentatively ascribed to its low stability for easily releasing the CO2 moiety and/or the desired product, a possible rate-limiting step in the catalytic cycle.

Silver(I)-catalyzed carboxylation of arylboronic esters with CO2.

A variety of arylboronic esters were efficiently carboxylated with CO(2) using a simple AgOAc/PPh(3) catalyst, affording the corresponding carboxylic acids in good yield. This simple and efficient silver(i) catalytic system showed wide functional group compatibility.