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1.
Org Lett ; 2020 Jun 02.
Artigo em Inglês | MEDLINE | ID: mdl-32484695

RESUMO

Addition of P-H species to carbonyl groups, namely the Pudovik reaction, normally delivers hydroxyl phosphorus compounds, along with phosphate byproducts in some cases. A few controllable systems starting from phosphites were set up to mainly provide the phosphates. Herein, we present a highly selective protocol starting from phosphonate precursors leading to phosphinate derivatives. Enantioenriched phosphinates were successfully achieved from chiral phosphine oxide precursors. Experimental and theoretical investigations were conducted to understand the mechanistic details.

2.
Org Lett ; 2020 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-32539418

RESUMO

Here, an interesting palladium-catalyzed intermolecular Heck-type dearomative [4 + 2] annulation of 2H-isoindole derivatives with internal alkynes has been developed, affording diverse polycyclic pyrrolidine scaffolds in good yield. This reaction is a useful method for the transformation of 2H-isoindole.

3.
Org Lett ; 22(13): 5229-5234, 2020 Jul 02.
Artigo em Inglês | MEDLINE | ID: mdl-32558574

RESUMO

Various new transformations of gem-difluoroalkenes leading to trifluoromethyl substituted compounds have been well established in the past years. However, the development of new transformations of gem-difluoroenynes lags much behind. Herein is reported the fluoroarylation of 1,1-difluoro-1,3-enynes with aryl halides in the presence of silver fluoride affording trisubstituted trifluoromethyl allenes under the catalysis of palladium. The reaction features mild conditions, high functional-group tolerance, and high regioselectivity.

4.
Chem Commun (Camb) ; 2020 May 27.
Artigo em Inglês | MEDLINE | ID: mdl-32458871

RESUMO

Herein, we have developed a novel and simple protocol to realize the C-H bond functionalization/dearomatization of naphthols and phenols with ortho-alkynylaryl-α-diazoesters under gold(i) catalysis. In this protocol, various spirocyclic molecules could be obtained in good yields with excellent chemo- and regio-selectivity and moderate to good diastereoselectivity.

5.
Artigo em Inglês | MEDLINE | ID: mdl-32395980

RESUMO

Rationally engineering the surface physicochemical properties of nanomaterials can improve their activity and durability for various electrocatalytic and energy conversion applications. Cu-Pd/Ir (CPI) nanospheres (NSs) anchored on N-doped porous graphene (NPG) [(CPI NSs/NPG)] have been recently demonstrated as a promising electrocatalyst for the alkaline ethanol oxidation reaction (EOR); to further enhance their electrocatalytic performance, the NPG-supported CPI NSs are coated with Au submonolayer (SML) shells (SMSs), through which their surface physicochemical properties can be tuned. CPI NSs/NPG is prepared by our previously developed method and possesses the special structures of composition-graded Cu1Pd1 and surface-doped Ir0.03. The Au SMSs with designed surface coverages are formed via an electrochemical technology involving incomplete Cu underpotential deposition (UPD) and Au3+ galvanic replacement. A distinctive volcano-type relation between the EOR electrocatalytic activity and the Au-SMS surface coverage for CPI@AuSML NSs/NPG is revealed, and the optimal CPI@Au1/6ML NSs/NPG greatly surpasses commercial Pd/C and CPI NSs/NPG in electrocatalytic activity and noble metal utilization. More importantly, its electrocatalytic durability in 1 h chronoamperometric and 500-cycle potential cycling degradation tests is also significantly improved. According to detailed physicochemical characterizations, electrochemical analyses, and density functional theory calculations, the promoting effects of the Au SMS for enhancing the EOR electrocatalytic activity and durability of CPI NSs/NPG can be mainly attributed to the greatly weakened carbonaceous intermediate bonding and properly increased surface oxidation potential. This work also proposes a versatile and effective strategy to tune the surface physicochemical properties of metal-based nanomaterials via incomplete UPD and metal-cation galvanic replacement for advancing their electrocatalytic and energy conversion performance.

6.
iScience ; 23(6): 101138, 2020 May 06.
Artigo em Inglês | MEDLINE | ID: mdl-32450512

RESUMO

Over the past decades, asymmetric catalysis has been intensely investigated as a powerful tool for the preparation of numerous chiral biologically active compounds. However, developing general and practical strategies for preparation of both enantiomers of a chiral molecule via asymmetric catalysis is still a challenge, particularly when the two enantiomers of a chiral catalyst are not easily prepared from natural chiral sources. Inspired by the biologic system, we report herein an unprecedented catalytic enantiodivergent Michael addition of pyridazinones to enones by subtle adjustment of achiral amino moiety of dipeptide phosphine catalysts. These two dipeptide phosphine catalysts, P5 and P8, could deliver both enantiomers of a series of N2-alkylpyridazinones in good yields (up to 99%) with high enantioselectivities (up to 99% ee) via the catalyst-controlled enantiodivergent addition of pyridazinones to enones.

7.
Org Lett ; 22(11): 4511-4516, 2020 Jun 05.
Artigo em Inglês | MEDLINE | ID: mdl-32403931

RESUMO

Herein, we described an efficient copper-catalyzed chemo-divergent tandem reaction of N-(ortho-alkynyl)aryl-pyrrole and (iso)indoles, delivering ring-fused N-heterocycles in good yields in an atom-economical manner. N-(ortho-alkynyl)aryl-pyrrole and indoles undergo the tandem cyclization/migration reaction, in which the group at 2-position was migrated to 3-position. In contrast, the dearomative cyclization of N-(ortho-alkynyl)aryl-isoindoles would occur to deliver the N-fused tetracyclic products efficiently.

8.
Artigo em Inglês | MEDLINE | ID: mdl-32412233

RESUMO

We report an effective approach to the synthesis of high-content and high-dispersion Pt nanoparticles (NPs) on XC-72 carbon black as a cathode electrocatalyst with improved high-current-density performance in proton exchange membrane fuel cells (PEMFCs). While exceptionally high catalytic activity for oxygen reduction reaction (ORR) was reported based on the rotating disk electrode (RDE) technique, such catalysts do not deliver nearly the same level of performance in PEMFC due to the lack of optimized design of catalyst structures on carbon support. We recently developed a synergistic synthesis method to make exceptionally high-content and finely dispersed Pt catalysts, which showed the highest Pt-electroactive surface area and the highest Pt mass activity for ORR among the electrocatalysts tested. More importantly, the membrane electrode assembly (MEA) made with this catalyst showed excellent performance at current densities higher than 1200 mA cm-2 in a hydrogen-air PEMFC measurement. 195Pt NMR was used to analyze the molecular structures of the metal precursors and to understand the mechanisms of the formation of Pt catalysts at high dispersity and uniformity.

9.
Chemistry ; 2020 May 19.
Artigo em Inglês | MEDLINE | ID: mdl-32427372

RESUMO

During the past few decades, there has been considerable growth in the development of denitrogenative reactions of triazole skeletons to construct valuable cyclic compounds, particularly heterocycles. Despite the inherent difficulty of the ring-opening of triazole derivatives, many novel and efficient approaches have arisen in this area mainly with the use of transition metal (such as rhodium, palladium, silver, copper) catalysis, photolysis, or free radical mediated reactions. Generally, these procedures begin with the ring-opening of 1,2,3-triazoles or benzotriazoles followed by N2 extrusion and subsequent diverse transformations, which enable the rapid synthesis of various heterocycles in a single step. To avoid overlap with other related reviews, this minireview covers the recent advances in the denitrogenative cyclization of 1,2,3-triazoles since 2016 and the denitrogenative cyclization of benzotriazoles since 2012.

10.
Nanoscale ; 12(26): 13858-13878, 2020 Jul 14.
Artigo em Inglês | MEDLINE | ID: mdl-32426790

RESUMO

For the purpose of redesigning a PEM fuel cell with ultralow Pt loading, this review comprehensively summarizes and comments on recent important findings on ultrathin catalyst layer structures. We introduce recent advances in electrocatalyst research and development (R&D), highlighting the urgency of ultralow Pt loading in the total design of PEM fuel cells. Following that, the reason for a thinner and more ordered electrode structure is presented for the next generation of PEM fuel cells. We then review recent progress in methods for preparing Pt nanoparticles on high-aspect-ratio supports, extended surface area of nanowires (confined agglomerates and nanowires) and ordered arrays. Regarding the ordered arrays, we expatiate on proton conductor arrays and electron conductor arrays, including carbon nanotube-assisted arrays, TiO2 nanotube-assisted arrays, Co-OH-CO3 nanowire-assisted arrays, and pigment red 149-assisted arrays. Challenges related to proton transport and transfer, electron conduction and mass transport are then discussed to supply further research direction.

11.
J Am Chem Soc ; 142(21): 9763-9771, 2020 May 27.
Artigo em Inglês | MEDLINE | ID: mdl-32336095

RESUMO

Enabled by the newly developed ligand, Ming-Phos, the first example of palladium-catalyzed highly enantioselective coupling of racemic propargylic benzoates with organoboronic acids for chiral allenes synthesis has been developed. Excellent asymmetric induction has been achieved with a decent substrate scope. Synthetic potentials for the construction of polycyclic compounds with multiple chiral centers have been demonstrated.

12.
Cancer Res ; 80(12): 2472-2483, 2020 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-32234710

RESUMO

Despite the fact that osteosarcoma is one of the most common primary bone malignancies with poor prognosis, the mechanism behind the pathogenesis of osteosarcoma is only partially known. Here we characterized differentially expressed genes by extensive analysis of several publicly available gene expression profile datasets and identified musculoaponeurotic fibrosarcoma oncogene homolog B (MAFB) as a key transcriptional regulator in osteosarcoma progression. MAFB was highly expressed in tumor tissues and required for proliferation and tumorigenicity of osteosarcoma cells. MAFB expression was elevated in osteosarcoma stem cells to maintain their self-renewal potential in vitro and in vivo through upregulation of stem cell regulator Sox9 at the transcriptional level. Sox9 in turn activated MAFB expression via direct recognition of its sequence binding enrichment motif on the MAFB locus, thereby forming a positive feedback regulatory loop. Sox9-mediated feedback activation of MAFB was pivotal to tumorsphere-forming and tumor-initiating capacities of osteosarcoma stem cells. Moreover, expression of MAFB and Sox9 was highly correlated in osteosarcoma and associated with disease progression. Combined detection of both MAFB and Sox9 represented a promising prognostic biomarker that stratified a subset of patients with osteosarcoma with shortest overall survival. Taken together, these findings reveal a MAFB-Sox9 reciprocal regulatory axis driving cancer stemness and malignancy in osteosarcoma and identify novel molecular targets that might be therapeutically applicable in clinical settings. SIGNIFICANCE: Transcription factors MAFB and Sox9 form a positive feedback loop to maintain cell stemness and tumor growth in vitro and in vivo, revealing a potential target pathway for therapeutic intervention in osteosarcoma.

13.
Nanoscale ; 2020 Mar 20.
Artigo em Inglês | MEDLINE | ID: mdl-32195530

RESUMO

With the conventional Haber-Bosch NH3 synthesis in industry requiring harsh pressures and high temperatures, artificial N2 fixation has been long sought after. The electrochemical nitrogen reduction reaction (NRR) could offer a solution by allowing NH3 production under ambient conditions. In this review, important recent findings on theoretical calculations and experimental exploration on the NRR at room temperature are systematically reviewed. Firstly, we discuss the mechanism of electrochemical heterogeneous catalysis for the NRR. The NRR is a multi-proton coupled electron transfer (PCET) process which implies that in addition to catalyst surface size effects, ligand and strain effects will also significantly influence the binding energy of the adsorbed N atoms, reaction intermediates and product species. Electrocatalysts including metals, metal nitrides, metal oxides and carbon-based materials will also be discussed at length. A linear scaling relationship seems to limit the NRR activity on most metals and metal oxides. Metal nitrides, however, follow the Mars-van Krevelen (MvK) mechanism which usually shows a lower potential energy barrier compared to the associative mechanism. Carbon-based materials and some single atom catalysts exhibit improved activity and selectivity due to ligand effects. Thus, electrolytes containing a proton donor might play a crucial role in the NRR. The limiting concentration of proton donors and the rate of proton transport to the active sites might be effective factors in boosting the selectivity of the NRR. Specifically, ionic liquids with high N2 solubility demonstrate much larger faradaic efficiency and would be promising candidates for use in NRR processes. Inspired by the characteristics of PCET, four strategies of electrode engineering were introduced including limiting protons, tuning the electron transport, modifying the electrode structure facilitating mass transport, and completely changing the NRR mechanism inspired by bio-nitrogenase and Li mediated N2 fixation.

14.
Metab Eng ; 59: 44-52, 2020 05.
Artigo em Inglês | MEDLINE | ID: mdl-32004707

RESUMO

Silymarin extracted from milk thistle seeds, is used for treating hepatic diseases. Silybin and isosilybin are its main components, and synthesized from coupling of taxifolin and coniferyl alcohol. Here, the biosynthetic pathways of taxifolin and coniferyl alcohol were reconstructed in Saccharomyces cerevisiae for the first time. To alleviate substantial burden caused by a great deal of genetic manipulation, expression of the enzymes (e.g. ZWF1, TYR1 and ARO8) playing multiple roles in the relevant biosynthetic pathways was selectively optimized. The strain YT1035 overexpressing seven heterologous enzymes and five native enzymes and the strain YC1053 overexpressing seven heterologous enzymes and four native enzymes, respectively produce 336.8 mg/L taxifolin and 201.1 mg/L coniferyl alcohol. Silybin and isosilybin are synthesized from taxifolin and coniferyl alcohol under catalysis of APX1t (the truncated milk thistle peroxidase), with a yield of 62.5%. This study demonstrates an approach for producing silybin and isosilybin from glucose for the first time.

15.
ACS Appl Mater Interfaces ; 12(1): 1677-1686, 2020 Jan 08.
Artigo em Inglês | MEDLINE | ID: mdl-31820630

RESUMO

Aramid nanofiber (ANF) paper has shown potential applications in flexible electronics. However, its inherent low thermal conductivity coefficient (λ) values might threaten the safety of devices under a high-power working condition. In this work, polydopamine-functionalized boron nitride nanosheet (BNNS@PDA)/ANF thermally conductive composite papers with nacre-mimetic layered structures were prepared via highly efficient vacuum-assisted filtration followed by hot pressing. For a given BNNS loading, the surface functionalization of BNNS could further enhance the thermal conductivities and mechanical properties of BNNS@PDA/ANF composite papers. BNNS@PDA/ANF composite papers presented anisotropic thermal conductivities, and the through-plane (λ⊥) and in-plane (λ∥) values of the 50 wt % BNNS@PDA/ANF composite papers reached 0.62 and 3.94 W/mK, 181.8 and 196.2% higher than those of original ANF paper, respectively, which were also higher than those of 50 wt % BNNS/ANF composite papers (λ⊥ = 0.52 W/mK and λ∥ = 3.33 W/mK). The tensile strength of the 50 wt % BNNS@PDA/ANF composite papers reached 36.8 MPa, 30.5% higher than that of 50 wt % BNNS/ANF composite papers (28.2 MPa). In addition, the heat resistance index (THRI) of the 50 wt % BNNS@PDA/ANF composite papers was further increased to 223.1 °C. Overall, our fabricated BNNS@PDA/ANF composite papers possess highly thermal conductivities, excellent mechanical robustness and flexibility, and outstanding thermal stabilities, showing great potential applications in the fields of intelligent wearable equipment, flexible supercapacitors, and flexible electronics.

16.
Mol Med Rep ; 21(2): 909-917, 2020 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-31789406

RESUMO

Upregulation of fetal hemoglobin expression can alleviate the severity of ß­thalassaemia. This study aimed to investigate the effects of Oridonin (ORI, a diterpenoid compound) on γ­globin expression in human erythroid precursor cells and the potential underlying mechanisms. Erythroid precursor cells were enriched from 12 patients with ß­thalassaemia by two­phase culture. The cells were then treated with different doses of ORI and the survival of erythroid precursor cells was determined. In addition, the expression levels of γ­globin and potential mechanisms were analyzed by reverse transcription­quantitative PCR, western blotting and chromatin immunoprecipitation. Treatment with 0.5 µM ORI preferably enhanced γ­globin expression and exhibited little cytotoxicity. Similar to sodium butyrate (NaB, a histone deacetylase inhibitor), ORI significantly increased p38 mitogen­activated protein kinase (MAPK) activation, γ­globin expression, histone H3 and H4 acetylation at the Gγ­ and Aγ­globin promoters, and cAMP­response element binding protein 1 (CREB1) phosphorylation. These effects were significantly mitigated by treatment with SB23580, a p38 MAPK inhibitor, in erythroid precursor cells. Therefore, ORI may effectively enhance γ­globin expression by activating p38 MAPK and CREB1, leading to histone modification in γ­globin gene promoters during the maturation of erythroid precursor cells. These findings suggested that ORI may be a novel and potential therapeutic agent for the treatment of ß­thalassaemia.

17.
Angew Chem Int Ed Engl ; 59(7): 2769-2775, 2020 Feb 10.
Artigo em Inglês | MEDLINE | ID: mdl-31755165

RESUMO

Sonogashira-type cross-couplings are one of the most significant alkynylations in organic chemistry. One of the first palladium-catalyzed intramolecular Heck/Sonogashira reactions of alkenes with terminal alkynes is now reported. With this method, a variety of uniquely substituted chiral benzene-fused heterocycles bearing a propargyl-substituted all-carbon quaternary stereocenter were obtained in a straightforward, high-yielding, and highly stereoselective manner under mild conditions. Salient features of this process include the use of readily available substrates, high selectivities, a broad substrate scope as well as versatile product functionalizations.

18.
Angew Chem Int Ed Engl ; 59(11): 4421-4427, 2020 Mar 09.
Artigo em Inglês | MEDLINE | ID: mdl-31868991

RESUMO

Reported here is a highly efficient Pd/Xiang-Phos catalyzed enantioselective carboetherification of alkenyl oximes with either aryl or alkenyl halides, delivering various chiral 3,5-disubstituted and 3,5,5-trisubstituted isoxazolines in good yields with up to 97 % ee. The sterically bulky and electron-rich (S,Rs)-NMe-X2 ligand is responsible for the excellent reactivities and enantioselectivities. The salient features of this transformation include mild reaction conditions, general substrate scope, good functional-group tolerance, good yields, high enantioselectivities, easy scale-up, and application in the late-stage modification of bioactive compounds. The obtained products can be readily transformed into useful chiral 1,3-aminoalcohols.

19.
J Am Chem Soc ; 141(51): 20556-20564, 2019 Dec 26.
Artigo em Inglês | MEDLINE | ID: mdl-31790237

RESUMO

The development of transition-metal-catalyzed methods for the synthesis of P-chiral phosphine derivatives poses a considerable challenge. Herein, we present a direct Pd/Xiao-Phos-catalyzed cross-coupling reaction of easily accessible secondary phosphine oxides and aryl bromides, which provides rapid access to P-chiral phosphine oxides. The reaction proceeds efficiently with a wide array of reaction partners to deliver various tertiary phosphine oxides in up to 96% yield and 97% ee. Moreover, the synthesis of DiPAMP ligand and its analogues was also realized, which demonstrates a suitable pathway to switching the branched chain of DiPAMP.

20.
Biol Trace Elem Res ; 2019 Dec 17.
Artigo em Inglês | MEDLINE | ID: mdl-31845206

RESUMO

Selenium (Se) is one of the essential elements required to maintain human health. Although various kinds of Se supplements are now available on the market, their biological activities and toxicities vary based on the transportation characteristics of Se. In this study, we compared the absorption and distribution of Se in rats administered with different Se supplements: Se-enriched Bifidobacterium longum DD98 (Se-DD98), selenized yeast (Se-Y), and sodium selenite (Na2SeO3). Se-DD98, Se-Y, and Na2SeO3 were orally administered to rats. The plasma Se content at different time points after administration was determined within 72 h. Pharmacokinetic parameters were analyzed to reveal the absorption of Se. Se-DD98, Se-Y, and Na2SeO3 were also repeatedly administered by oral gavage for 30 days, and Se content of the heart, liver, spleen, lungs, kidneys, and muscle was determined to analyze the distribution of Se. The results showed that the organic Se supplements (Se-DD98 and Se-Y) were more easily absorbed into the blood and retained longer in the plasma than the inorganic Na2SeO3 was. Moreover, Se-DD98 induced better absorption of Se in plasma than Se-Y did. Furthermore, significantly higher concentrations of Se were found in the heart, liver, spleen, kidneys, and muscle of rats administered with organic Se supplements (Se-DD98 and Se-Y) than those administered the inorganic Na2SeO3. Rats administered Se-DD98 accumulated more Se in the spleen, lung, and kidney than those administered Se-Y, while Se-Y led to higher concentration of Se in the liver compared to Se-DD98. These results suggest that the organic form of Se was better absorbed and accumulated than the inorganic form was. Se-enriched B. longum DD98 induced greater absorption of Se in plasma and accumulation of Se in several organs than the selenized yeast did, which could suggest the potential superior nutritional function of Se-DD98.

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