| 1. |
- Andersson, Hans, et al.
(författare)
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Complete regioselective addition of grignard reagents to pyrazine N-oxides, toward an efficient enantioselective synthesis of substituted piperazines.
- 2010
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Ingår i: Organic letters. - : American Chemical Society (ACS). - 1523-7052 .- 1523-7060. ; 12:2, s. 284-6
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Tidskriftsartikel (refereegranskat)abstract
- A conceptually new one-pot strategy for the synthesis of protected substituted piperazines via the addition of Grignard reagents to pyrazine N-oxides is presented. This strategy is high yielding (33-91% over three steps), step-efficient, and fast. The synthesized N,N-diprotected piperazines are convenient to handle and allow for orthogonal deprotection at either nitrogen for selective transformations. In addition, this is a synthetic route to enantiomerically enriched piperazines by using a combination of phenyl magnesium chloride and (-)-sparteine, which resulted in enantiomeric excesses up to 83%.
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| 2. |
- Basu, Basudeb, et al.
(författare)
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Palladium supported on a Polyionic Resin as an efficient, ligand-free, and recyclable catalyst for Heck, Suzuki-Miyaura, and Sonogashira reactions
- 2009
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Ingår i: Synthesis (Stuttgart). - Stuttgart, New York : Georg Thieme Verlag. - 0039-7881 .- 1437-210X. ; :7, s. 1137-1146
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Tidskriftsartikel (refereegranskat)abstract
- Polyionic Amberlite resin formate (ARF), derived from commercially available Amberlite resin chloride by simple rinsing with aqueous formic acid, could be soaked with palladium(0) from palladium salts, the formate counteranion being the reducing source. The resulting Amberlite resin formate supported with palladium(0), ARF-Pd, showed excellent catalytic activity in Heck, Suzuki-Miyaura, and Sonogashira couplings with a range of substrates. The catalyst may be recovered easily and quantitatively without leaching and recycled; it was tested for five runs without any significant loss of activity.
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| 3. |
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| 4. |
- Chorell, Erik, 1980-, et al.
(författare)
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Diverse functionalization of Thiazolo ring-fused 2-Pyridones
- 2007
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Ingår i: Journal of Organic Chemistry. - Washington, DC 20036, USA : American Chemical Society. - 0022-3263 .- 1520-6904. ; 72:13, s. 4917-4924
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Tidskriftsartikel (refereegranskat)abstract
- Thiazolo ring-fused 2-pyridones have proven to be highly interesting scaffolds for the development of biologically active compounds. Many methods are today available to introduce a variety of substituents in the 2-pyridone part of the heterocycle. Herein we disclose how a diverse set of substituents can be introduced in the thiazolo ring, with possibilities to vary also the spatial arrangement of the substituents. A key intermediate is the oxidized framework 9 for which an effective synthesis is described. The thiazolo part of this system can be substituted either via conjugate additions, resulting in trans selectivity, or via microwave-assisted Heck couplings that result in unsaturated aryl-substituted analogues. The scaffold can also be lithiated followed by the addition of various electrophiles, which increases the diversification potential substantially, as exemplified with the introduction of halogens, alkyl, acyl, and amide substituents.
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| 5. |
- Chorell, Erik, et al.
(författare)
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Synthesis and application of a bromomethyl substituted scaffold to be used for efficient optimization of anti-virulence activity
- 2011
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Ingår i: European Journal of Medicinal Chemistry. - : Elsevier Masson SAS. - 0223-5234 .- 1768-3254. ; 46:4, s. 1103-1116
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Tidskriftsartikel (refereegranskat)abstract
- Pilicides are a class of compounds that attenuate virulence in Gram negative bacteria by blocking the chaperone/usher pathway in Escherichia coli. It has also been shown that compounds derived from the peptidomimetic scaffold that the pilicides are based on can prevent both Aβ aggregation and curli formation. To facilitate optimizations towards the different targets, a new synthetic platform has been developed that enables fast and simple introduction of various substituents in position C-7 on the peptidomimetic scaffold. Importantly, this strategy also enables introduction of previously unattainable heteroatoms in this position. Pivotal to the synthetic strategy is the synthesis of a C-7 bromomethyl substituted derivative of the ring-fused dihydrothiazolo 2-pyridone pilicide scaffold. From this versatile and reactive intermediate various heteroatom-linked substituents could be introduced on the scaffold including amines, ethers, amides and sulfonamides. In addition, carbon-carbon bonds could be introduced to the sp(3)-hybridized bromomethyl substituted scaffold by Suzuki-Miyaura cross couplings. Evaluation of the 24 C-7 substituted compounds in whole-bacterial assays provided important structure-activity data and resulted in the identification of a number of new pilicides with activity as good or better than those developed previously.
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| 6. |
- Mukherjee, Sumanta, et al.
(författare)
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Determination of Internal Structures of Heterogeneous Nanocrystals Using Variable-Energy Photoemission Spectroscopy
- 2014
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 118:28, s. 15534-15540
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Tidskriftsartikel (refereegranskat)abstract
- This article describes the determination of the internal structure of heterogeneous nanoparticle systems including inverted core-shell (CdS core and CdSe shell) and alloyed (CdSeS) quantum dots using depth-resolved, variable-energy X-ray photoelectron spectroscopy (XPS). A unique feature of this work is the combination of photoelectron spectroscopy performed at lower X-ray energies (400-700 eV), to achieve surface sensitivity, with bulk sensitive measurements at high photon energies (>2000 eV), thereby providing detailed information about the whole nanoparticle structure with a great accuracy. The use of high photon energies furthermore allows us to investigate nanoparticles much larger than those studied thus far. This capability is a consequence of the much-increased mean free path of the photoelectron achieved at high excitation energies. Our results show that the actual structures of the synthesized nanoparticles are considerably different from the nominal, targeted structures, which can be post facto rationalized in terms of the reactivity of different constituents.
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| 7. |
- Mukherjee, Soham, et al.
(författare)
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Microscopic description of the evolution of the local structure and an evaluation of the chemical pressure concept in a solid solution
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 89:22, s. 224105-
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Tidskriftsartikel (refereegranskat)abstract
- Extended x-ray absorption fine-structure studies have been performed at the Zn K and Cd K edges for a series of solid solutions of wurtzite Zn1-xCdxS samples with x = 0.0, 0.1, 0.25, 0.5, 0.75, and 1.0, where the lattice parameter as a function of x evolves according to the well-known Vegard's law. In conjunction with extensive, large-scale first-principles electronic structure calculations with full geometry optimizations, these results establish that the percentage variation in the nearest-neighbor bond distances are lower by nearly an order of magnitude compared to what would be expected on the basis of lattice parameter variation, seriously undermining the chemical pressure concept. With experimental results that allow us to probe up to the third coordination shell distances, we provide a direct description of how the local structure, apparently inconsistent with the global structure, evolves very rapidly with interatomic distances to become consistent with it. We show that the basic features of this structural evolution with the composition can be visualized with nearly invariant Zn-S-4 and Cd-S-4 tetrahedral units retaining their structural integrity, while the tilts between these tetrahedral building blocks change with composition to conform to the changing lattice parameters according to the Vegard's law within a relatively short length scale. These results underline the limits of applicability of the chemical pressure concept that has been a favored tool of experimentalists to control physical properties of a large variety of condensed matter systems.
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| 8. |
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| 9. |
- Åberg, Veronica, 1976-, et al.
(författare)
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Carboxylic acid isosteres improve the activity of ring-fused 2-pyridones that inhibit pilus biogenesis in E. coli
- 2008
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Ingår i: Bioorganic & Medicinal Chemistry Letters. - : Elsevier Ltd. - 0960-894X. ; 18:12, s. 3536-3540
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Tidskriftsartikel (refereegranskat)abstract
- Ring-fused 2-pyridones, termed pilicides, are small synthetic compounds that inhibit pilus assembly in uropathogenic Escherichia coli. Their biological activity is clearly dependent upon a carboxylic acid functionality. Here, we present the synthesis and biological evaluation of carboxylic acid isosteres, including, for example, tetrazoles, acyl sulfonamides, and hydroxamic acids of two lead 2-pyridones. Two independent biological evaluations show that acyl sulfonamides and tetrazoles significantly improve pilicide activity against uropathogenic E. coli.
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