A series of novel tricyclic quinazolinone-iminosugars 5 and their derivatives 7 were obtained from the tosylated sugars by three steps. Firstly, the reaction of the isopropylidene protected sugar tosylate 1 and o-aminobenzylamine 2 generated the precursor-tricyclic quinazolin-iminosuar 3, which was then oxidized by KMnO4 to produce the corresponding quinazolinone 4. Finally, removal of the isopropylidene group yielded the target tricyclic quinazolinone iminosugars 5. In addition, quinazolinone-iminosugars 4ac, 4bc and 4cc who contain bromine in the aromatic region underwent Suzuki reaction with phenylboronic acid, followed with the removal of the isopropylidene group to afford the derivatives 7. This strategy will help to construct such fused multicyclic quinazolinone-iminosugars efficiently. Some compounds show certain inhibition against α-glucosidase (saccharomyce cerevisiae).
Abstract The extinction property of a two species competitive stage-structured phytoplankton system with harvesting is studied in this paper. Several sets of sufficient conditions which ensure that one of the components will be driven to extinction are established. Our results supplement and complement the results of Li and Chen [Extinction in periodic competitive stage-structured Lotka-Volterra model with the effects of toxic substances, J. Comput. Appl. Math., 2009, 231(1), 143-153] and Liu, Chen, Luo et al. [Extinction and permanence in nonautonomous competitive system with stage structure, J. Math. Anal. Appl., 2002, 274(2), 667-684].
A Rh(II)-catalyzed oxy-alkynylation of acceptor-acceptor carbenes using EBX reagents was successfully developed. The key alkyne-transfer step is likely to occur through a tandem process involving a β-addition, an α-elimination, and a 1,2-shift, which was supported by the formation of alkylidene carbene. Various diverse C2-quaternary alkyne-substituted benzofuran-3-ones and 2,2,4,5-tetrasubstituted 3(2H)-furanones can be synthesized smoothly, depending on the choice of diazo compounds and the base additives. Furthermore, this reaction is characterized by mild conditions, high functional group compatibility, and a broad substrate scope.
In this paper, a two species amensalism model with Michaelis–Menten type harvesting and a cover for the first species that takes the form $$\begin{aligned} &\frac{dx(t)}{dt}=a_{1}x(t)-b_{1}x^{2}(t)-c_{1}(1-k)x(t)y(t)- \frac{qE(1-k)x(t)}{m_{1}E+m_{2}(1-k)x(t)}, \\ &\frac{dy(t)}{dt}=a_{2}y(t)-b_{2}y^{2}(t) \end{aligned}$$ is investigated, where $a_{i}$ , $b_{i}$ , $i=1,2$ , and $c_{1}$ are all positive constants, k is a cover provided for the species x, and $0< k<1$ . The stability and bifurcation analysis for the system are taken into account. The existence and stability of all possible equilibria of the system are investigated. With the help of Sotomayor's theorem, we can prove that there exist two saddle-node bifurcations and two transcritical bifurcations under suitable conditions.
A Rh(II)/Pd(0) dual-catalysis strategy that promotes the regio-divergent transformations of alkylic oxonium ylides from α-diazo-β-ketoesters has been developed. Polyfunctionalized dihydrofuran-3-ones with an O-substituted quaternary carbon center and 2,3-disubstituted benzofurans can be selectively obtained in good to excellent yields at room temperature via one-pot synthesis. The reaction mechanism was further investigated by the control, stepwise, and crossover experiments.
A new certified reference material (CRM) of D-mannitol (GBW(E) 100681) has been developed in this study. We describe the preparation, structure determination, characterization, homogeneity study, stability study, as well as uncertainty estimation. The main component was 99.91% ± 0.01%. The moisture content of the candidate CRM was 0.036% ± 0.002%, as measured by Karl Fischer titration. The nonvolatile and volatile impurities in the candidate CRM were all much less than 0.01%, which was determined by the ICP-MS and headspace GC-FID methods, respectively. The purity of the D-mannitol CRM was 99.9% ± 1.1% (k = 2), as measured by the two independent approaches involving the mass balance method (MB) and quantitative nuclear magnetic resonance technique (qNMR). The D-mannitol CRM was stable during the monitoring period for each temperature. It is stable for up to 48 months at room temperature and 28 days at 50 °C. The uncertainty was evaluated by combining the contributions from characterization, homogeneity, and stability. The developed D-mannitol CRM would effectively support method validation and proficiency testing, as well as effectively guarantee the accuracy, reliability, and comparability of results.
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