177,069 research outputs found
Network-analysis-guided synthesis of weisaconitine D and liljestrandinine.
General strategies for the chemical synthesis of organic compounds, especially of architecturally complex natural products, are not easily identified. Here we present a method to establish a strategy for such syntheses, which uses network analysis. This approach has led to the identification of a versatile synthetic intermediate that facilitated syntheses of the diterpenoid alkaloids weisaconitine D and liljestrandinine, and the core of gomandonine. We also developed a web-based graphing program that allows network analysis to be easily performed on molecules with complex frameworks. The diterpenoid alkaloids comprise some of the most architecturally complex and functional-group-dense secondary metabolites isolated. Consequently, they present a substantial challenge for chemical synthesis. The synthesis approach described here is a notable departure from other single-target-focused strategies adopted for the syntheses of related structures. Specifically, it affords not only the targeted natural products, but also intermediates and derivatives in the three families of diterpenoid alkaloids (C-18, C-19 and C-20), and so provides a unified synthetic strategy for these natural products. This work validates the utility of network analysis as a starting point for identifying strategies for the syntheses of architecturally complex secondary metabolites
An investigation of the formation and line properties of MgH in 3D hydrodynamical model stellar atmospheres
Studies of the isotopic composition of magnesium in cool stars have so far
relied upon the use of one-dimensional (1D) model atmospheres. Since the
isotopic ratios derived are based on asymmetries of optical MgH lines, it is
important to test the impact from other effects affecting line asymmetries,
like stellar convection. Here, we present a theoretical investigation of the
effects of including self-consistent modeling of convection. Using spectral
syntheses based on 3D hydrodynamical COBOLD models of dwarfs
(4000K, log(g),
) and giants (K,
log(g), ), we perform a detailed
analysis comparing 3D and 1D syntheses.
We describe the impact on the formation and behavior of MgH lines from using
3D models, and perform a qualitative assessment of the systematics introduced
by the use of 1D syntheses.
Using 3D model atmospheres significantly affect the strength of the MgH
lines, especially in dwarfs, with 1D syntheses requiring an abundance
correction of up to +0.69 dex largest for our 5000K models. The corrections are
correlated with and are also affected by the metallicity. The
shape of the strong MgH component in the 3D syntheses is poorly
reproduced in 1D. This results in 1D syntheses underestimating MgH by up
to percentage points and overestimating MgH by a similar amount
for dwarfs. This discrepancy increases with decreasing metallicity. MgH
is recovered relatively well, with the largest difference being
percentage points. The use of 3D for giants has less impact, due to smaller
differences in the atmospheric structure and a better reproduction of the line
shape in 1D.Comment: 20 pages, 15 figures, accepted for publication in Ap
Pd-catalyzed enantioselective aerobic oxidation of secondary alcohols: Applications to the total synthesis of alkaloids
Enantioselective syntheses of the alkaloids (-)-aurantioclavine, (+)-amurensinine, (-)-lobeline, and (-)- and (+)-sedamine are described. The syntheses demonstrate the effectiveness of the Pd-catalyzed asymmetric oxidation of secondary alcohols in diverse contexts and the ability of this methodology to set the absolute configuration of multiple stereocenters in a single operation. The utility of an aryne C-C insertion reaction in accessing complex polycyclic frameworks is also described
Review: Marine natural products
This review covers the literature published in 2003 for marine natural products, with 619 citations (413 for the period January to December 2003) referring to compounds isolated from marine microorganisms and phytoplankton, green algae, brown algae, red algae, sponges, coelenterates, bryozoans, molluscs, tunicates and echinoderms. The emphasis is on new compounds (656 for 2003), together with their relevant biological activities, source organisms and country of origin. Biosynthetic studies or syntheses that lead to the revision of structures or stereochemistries have been included (78), including any ďŹrst total syntheses of a marine natural product
Syntheses of (+)-30-epi-, (-)-6-epi-, (Âą)-6,30-epi-13,14-didehydroxyisogarcinol and (Âą)-6,30-epi-garcimultiflorone A utilizing highly diastereoselective, Lewis acid-controlled cyclizations
The first syntheses of 13,14-didehydroxyisogarcinol (6) and garcimultiflorone A (5) stereoisomers are reported in six steps from a commercially available phloroglucinol. Lewis acid-controlled, diastereoselective cationic oxycyclizations enabled asymmetric syntheses of (-)-6-epi-6 and (+)-30-epi-6. A similar strategy enabled production of the meso-dervied isomers (Âą)-6,30-epi-6 and (Âą)-6,30-epi-5. Finally, a convenient strategy for gram scale synthesis was developed utilizing diastereomer separation at a later stage in the synthesis that minimized the number of necessary synthetic operations to access all possible stereoisomers.R01 GM073855 - NIGMS NIH HHS; R24 GM111625 - NIGMS NIH HHS; R35 GM118173 - NIGMS NIH HH
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Production of high molecular weight organic compounds on the surfaces of amorphous iron silicate catalysts: Implications for organic synthesis in the solar nebula
The high molecular weight organic products of Fischer-Tropsch/Haber-Bosch syntheses on the surfaces of Fe-silicate catalysts have been studied by GCMS
A Simpler Route for Making Nitrogen-Alkene Rings
A common nitrogen building block used in many natural product and drug syntheses can now be made in its unprotected form in a single step.</jats:p
N-Triflylphosphorimidoyl Trichloride: A Versatile Reagent for the Synthesis of Strong Chiral Brønsted Acids
A series of strong Brønsted acids has been synthesized in high yields using N-triflylphosphorimidoyl trichloride as reagent. The syntheses proceed efficiently with electron-rich, electron-deficient, and sterically hindered substrates
Exploratory polymer synthesis Quarterly status report, 1 May - 31 Jul. 1969
Syntheses and reactions of pyridine type monomer
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