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121.
A synthesis of novel 3,5-disubstituted isoxazole–carbohydrate conjugates is described. The title compounds are obtained from 3-deoxy-3-C-nitromethyl derivatives of 1,2:5,6-di-O-isopropylidene-α-d-glucofuranose via nitrile oxide intermediates. The developed approach provides the first examples of isoxazolyl sugars where the azole fragment is attached to C(3) of the carbohydrate through a C–C bond. Isoxazoles can be valuable linkers in glycoconjugate chemistry and this is demonstrated by the synthesis of a glycocluster containing five carbohydrate residues attached to a central glucose platform. 相似文献
122.
2,6-Diazidopurine derivatives undergo double azide–alkyne 1,3-dipolar cycloaddition (CuAAC) reactions to give 2,6-bis-(triazolyl)purine analogs, which undergo selective nucleophilic aromatic substitution with various thiols at C(6). This synthetic sequence produces nucleoside analogs with 6-alkyl/arylthio-2-(4-alkyl/aryl-1H-1,2,3-triazol-1-yl)purine bases. In contrast, glycosylated 2,6-diazidopurines exhibit reasonable C(2) selectivity in nucleophilic aromatic substitution with thiols. This permits the synthesis of 2-alkylthio-6-azido-purine derivatives, which after CuAAC provide the corresponding 2-alkylthio-6-triazolyl-purine analogs. The latter are also susceptible to nucleophilic aromatic substitution with amines at C(6). The above mentioned compounds are useful molecular platforms in terms of medicinal chemistry. 相似文献
123.
János Madarász Edit Székely Judit Halász György Bánsághi Dániel Varga Béla Simándi György Pokol 《Journal of Thermal Analysis and Calorimetry》2013,111(1):567-574
Two different compounds have formed from liquid enantiomeric (R-) and racemic α-methylbenzylamine (α-MBA, named also as 1-phenylethylamine, 1-FEA) with supercritical fluid CO2. The crystalline solids have been characterized by elemental CHN analysis, X-ray diffraction (XRD), FTIR, 1H, and 13C NMR spectroscopy, and found to be α-methylbenzylammonium α-methylbenzylcarbamate self-derivative ionic salts 1 (R/R) and 2 (rac RS), respectively, of the corresponding amines. Compound 2 (rac RS) has shown different XRD pattern from that of enantiomerically pure 1 (R/R), indicating a preferential formation of a 1:1 mixture of (R/S-) and (S/R-) or rather a racemate compound of (RS/SR-) ammonium carbamate salt (2 (rac RS)) from racemate. For thermal stability, the compounds have been checked by differential scanning calorimetry (DSC), simultaneous thermogravimetry and differential thermal analysis (TG/DTA), and in situ coupled evolved gas analysis by mass spectroscopy (TG/DTA?EGA?MS) and FTIR-gas cell (TG?FTIR). No melting point is observed because of the low thermal stability of the compounds. Decomposition stages are tried to be separated with using semi-closed (sealed with a pinhole on the top) crucibles, thus different evolution courses of CO2 and organic vapors could be followed by MS and FTIR spectroscopy. The α-MBA vapors themselves, evolved from open crucibles could be identified by FTIR-gas cell, while vapors up to m/z = 164 have been detected by MS from semi-closed Al crucible. 相似文献
124.
Based on segmentation-recombination principle, a specific optical device is designed to homogenize a highpower CO2 laser beam which is used as a heating source. 相似文献
125.
Mechanical design of the recirculating, terminal pumping in the lund pelletron, and experimental experience 总被引:1,自引:0,他引:1
A recirculating terminal pumping system has been installed in the 3 MV Pelletron tandem accelerator in Lund. An extremly limited
space in the high voltage terminal and the absence of electrical power in the terminal, forced us to provide a unique design
for the installation and powering of the new pumps. Details of the technical design, as well as experience of the use of the
new system for accelerator mass spectrometry, will be given. 相似文献
126.
A well known chaotic mapping in symbol space is a shift mapping.However,other chaotic mappings in symbol space exist too.The basic change is to consider the process not only at a set of times which are equally spaced,say at unit time apart(a shift mapping),but at a set of times which are not equally spaced,say if the unit time can not be fixed.The increasing mapping as a generalization of the shift mapping and the k-switch mapping are introduced.The increasing and k-switch mappings are chaotic. 相似文献
127.
Peculiarities of colour centres production and their recombination in photostimulated processes in doped alkali halide microstructures were examined in connection with their practical use as active photostimulable media in miniaturised optoelectronic and photonic devices. The specific interaction of unrelaxed H-centres and electrons with the dopants in different valence and electronic states open a way for widening the scope of multifunctional (logical and mathematical) optical data processing and transfer. 相似文献
128.
Larisa Gigorjeva Donats Millers Jānis Grabis Dzidra Jankoviča 《Central European Journal of Physics》2011,9(2):510-514
ZnWO4 powders with grain size in range 20 nm–10 μm have been synthesized by a simple combustion method and subsequent calcinations.
The photocatalytic activities of powders were tested by degradation of methylene blue solution under UV light. The luminescence
spectra and luminescence decay kinetics were studied and luminescence decay time dependence on average powder-grain size was
obtained. The correlation between self-trapped exciton luminescence decay time and photocatalytic activity of ZnWO4 powders was shown. A model explaining the excitonic luminescence decay time correlation with photocatalytic activity was
proposed. 相似文献
129.
130.
Inta StrakovaIlze Kumpi?a Vitālijs RjabovsJevge?ija Lugi?ina Sergey BelyakovMāris Turks 《Tetrahedron: Asymmetry》2011,22(7):728-739
The chiral resolution of 7-amino-1-aryl-4,5,6,7-tetrahydro-indazol-4-ones was achieved via salt formation with O,O′-dibenzoyl tartaric acid. The transformation of enantiomerically enriched 7-amino-THIs into their corresponding azides proceeds with no decrease in their ee’s. A comparison of the X-ray structures of the racemic and enantiopure forms of the title compounds explains the rather large melting point differences between both the series. The enantiopure azides obtained from the corresponding 7-amino-THIs were employed in copper-catalyzed Huisgen 1,3-dipolar cycloaddition reactions with various alkynes. The use of enantiomerically enriched THI scaffolds is demonstrated by the preparation of diastereomerically pure products when the former are conjugated with alkynes arising from natural sources. 相似文献