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31.
The nitrosation of some γ,δ-unsaturated β-diketo compounds affords the 3-substituted 4-oxo-5,6-dihydro-1,2,4H-oxazines. These compounds are converted to the isomeric 3-oxo-1-pyrroline 1-oxides by a facile thermal rearrangement. 相似文献
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33.
Bernard Chantegrel Abdel-Ilah Nadi Suzanne Gelin 《Journal of heterocyclic chemistry》1985,22(4):1127-1128
A series of 3-alkenyl-4-oxo-6,7-dihydro-4H-pyrano[3,4-d]isoxazole derivatives was prepared by reaction of hydroxylamine with 4,5-dioxo-2,3,7,8-tetrahydro-4H,5H-pyrano[4,3-b]pyran derivatives. 相似文献
34.
Ramoplanin is a cyclicdepsipeptide antibiotic that inhibits peptidoglycan biosynthesis. It was proposed in 1990 to block the MurG step of peptidoglycan synthesis by binding to the substrate of MurG, Lipid I. The proposed mechanism of MurG inhibition has become widely accepted even though it was never directly tested. In this paper, we disprove the accepted mechanism for how ramoplanin functions, and we present an alternative mechanism. This work has implications for the design of ramoplanin derivatives and may influence how other proposed substrate binding antibiotics are studied. 相似文献
35.
Leclaire J Dagiral R Fery-Forgues S Coppel Y Donnadieu B Caminade AM Majoral JP 《Journal of the American Chemical Society》2005,127(45):15762-15770
The synthesis of a new family of phosphorus dendrimers built from an octasubstituted metal-free phthalocyanine core is described up to generation 5. This core is used as a sensor and a probe for analyzing the properties of the internal structure and the influence of each structural part (core, branches, surface) upon the whole structure. UV-visible spectra show both a hyperchromic and bathochromic effect on the Q-bands with increasing generation, indicating that the chromophore is more isolated, and that the dendritic shell mimics a highly polar solvent. There is no evidence for aggregation, except for generation 0, showing again the isolation of the core. However, the dendritic shell is permeable to aqueous acids and bases, as demonstrated by the reversible splitting of the Q-band in an acidic medium (neutral form of the phthalocyanine) and the single Q-band in a basic medium (dianionic form), even for generation 4. The fluorescence quantum yield for the neutral form increases with increasing generation. The dianionic form of generation 0 is poorly fluorescent, whereas generations 3 and 4 (G3 and G4) exhibit better fluorescence. The cores of G3 and G4 are highly sensitive optical sensors for H3O+ and OH-. These experiments are carried out in THF/water mixtures, and the influence of water on the structure has been checked. The hydrodynamic radius of generation 4 is measured by NMR diffusion (pulse gradient spin-echo) experiments. R(H) varies from 35.4 A at 4 mol % of water to 32.5 A at 64 mol % of water in THF, indicating the hydrophobic nature of these dendrimers. 相似文献
36.
Suzanne Gelin Bernard Chantegrel Christian Deshayes 《Journal of heterocyclic chemistry》1982,19(5):989-991
The synthesis and biological activities of some 4-oxo-1-or-2-substituted 1H-or-2H-pyrano[4,3-c]pyrazole derivatives are described. 相似文献
37.
L. Renee Ruhaak Sandra L. Taylor Suzanne Miyamoto Karen Kelly Gary S. Leiserowitz David Gandara Carlito B. Lebrilla Kyoungmi Kim 《Analytical and bioanalytical chemistry》2013,405(14):4953-4958
Many studies focused on the discovery of novel biomarkers for the diagnosis and treatment of disease states are facilitated by mass spectrometry-based technology. HPLC coupled to mass spectrometry is widely used; miniaturization of this technique using nano-liquid chromatography (LC)-mass spectrometry (MS) usually results in better sensitivity, but is associated with limited repeatability. The recent introduction of chip-based technology has significantly improved the stability of nano-LC-MS, but no substantial studies to verify this have been performed. To evaluate the temporal repeatability of chip-based nano-LC-MS analyses, N-glycans released from a serum sample were repeatedly analyzed using nLC-PGC-chip-TOF-MS on three non-consecutive days. With an average inter-day coefficient of variation of 4 %, determined on log10-transformed integrals, the repeatability of the system is very high. Overall, chip-based nano-LC-MS appears to be a highly stable technology, which is suitable for the profiling of large numbers of clinical samples for biomarker discovery. 相似文献
38.
Peter C. Ho Justin Lomax Valerie Tomassetti Dr. James F. Britten Dr. Ignacio Vargas-Baca 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(42):10849-10853
Chlorination of 3-methyl-5-phenyl-1,2-tellurazole-2-oxide yielded the λ4Te dichloro derivative. Its crystal structure demonstrates that the heterocycle retains its ability to autoassociate by chalcogen bonding (ChB) forming macrocyclic tetramers. The corresponding Te⋅⋅⋅O ChB distances are 2.062 Å, the shortest observed to date in aggregates of this type. DFT−D3 calculations indicate that while the halogenated molecule is stronger as a ChB donor it also is a weaker ChB acceptor; the overall effect is that the ChBs in the chlorinated homotetramer are not significantly stronger. However, partial halogenation or scrambling selectively yield the 2 : 2 heterotetramer with alternating λ4Te and λ2Te centers, which calculations identified as the thermodynamically preferred arrangement. 相似文献
39.
40.
Environmental Fenton chemistry has been poorly constrained within the marine environment at a multi-component level. A simple, unique, reconfiguration of a flow-injection analytical system combined with luminol chemiluminescence allows quasi-simultaneously the measurement, using a single load-inject valve and a single photon multiplier tube, of reduced iron, Fe(II), and hydrogen peroxide. The system enables rapid, every 22 s, measurements with good accuracy at environmentally relevant concentrations, less than 5% relative standard deviations on both a 5 nM Fe(II) standard and a 60 nM hydrogen peroxide standard. Limits of detection were as low as 40 pM Fe(II) and 100 pM hydrogen peroxide. The system showed excellent capability by measuring from within an organic rich seawater the photochemically induced production of Fe(II) and hydrogen peroxide and their subsequent cycling and Fenton like interactions. 相似文献