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1.
3-O-Acetyl-1,2-O-isopropylidene--D-allofuranose (2 b) was prepared from 1,2:5,6-di-O-isopropylidene--D-allofuranose (1 b). Treatment of2 b with triphenylphosphine-diethyl azodicarboxylate afforded regio- and stereospecifically the 5,6-epoxy--D-allo derivative (3). The other diastereomeric compound, 5,6-epoxy-1,2-O-isopropylidene--L-talofuranose (6) was also prepared stereoselectively from2 b
via the intermediates5 a and5 b. The epoxy sugars3 and6 were converted with lithium aluminum hydride to the corresponding 6-deoxy-1,2-O-isopropylidene--D-allofuranose (4 a) and --L-talofuranose (7 a) derivatives. Hydrolysis of4 a and7 a afforded 6-deoxy-D-allose and 6-deoxy-L-talose, respectively. The corresponding 3,5-di-O-acetyl- (4 b and7 b) and the 3,5-O-(tetraisopropyldisiloxane-1,3-diyl) derivatives (4 c and7 c) are also described. Selective removal of the isopropylidene group and subsequent acetylation offers a convenient route to prepare sugar derivatives containing furanose ring, like8 b, as a suitable precursor for nucleoside analogs.Herrn Prof. Dr.K. Komarek mit den besten Wünschen zum 60. Geburtstag gewidmet. 相似文献
2.
Pedro A. Fernandes Elsa S. Henriques Vineet Pande Maria. J. Ramos Ana R. R. Maia André A. S. Almeida Bruno F. B. Silva Carla M. S. Ribeiro César F. B. Ribeiro David S. M. Ribeiro Diana A. P. Fonseca Eva M. S. Cunha Filipe R. N. C. Maia Joana A. A. Pereira João P. G. Pacheco Joaquim A. A. D. Ferreira Liliana R. C. Matos Manuel A. B. P. Pinto Maria C. S. Borges Paulo J. C. R. Magalhães Pedro F. R. D. Teixeira Pedro N. B. C. Veloso Ricarte J. F. Ferreira Sandro S. Gomes Tiago F. Barros Tiago S. J. T. Selão Virgínia M. M. C. Fernandes 《Theoretical chemistry accounts》2005,113(4):197-204
We present a series of new inhibitors of the association between nuclear factor kappa B (NF-B) and the corresponding B site in DNA. They were designed using the lead compound 15-deoxy-12,14 -prostaglandin J2 (PGJ2), which is a natural product with demonstrated inhibitory efficiency for this system. First, the binding mode of PGJ2 to NF-B was unraveled by GOLD docking calculation. Subsequently, substitutions were made to PGJ2 to optimize its association with NF-B. Care was taken not to strongly increase the reactivity of the new compounds, and to keep the overall shape, size and hydrophilicity of the lead compound, which should render them a similar bioavailability. Molecular mechanics calculations were performed to decide on the suitability of the substitutions, and to evaluate the energies of association with NF-B. Density functional theory calculations were performed also to study the overall reactivity of the substituted drugs towards NF-B. Important general conclusions were obtained, concerning the improvement of these natural inhibitors; namely, a set of rational methodologies were deduced to improve the association between the PGJ2 derivatives and NF-B, and their efficiency demonstrated by generating a set of substituted complexes, some of them with a very much increased affinity for NF-B, opening new doors to enlarge the therapeutic capabilities of this class of drugs. 相似文献
3.
Summary 2-Aminopyridine reacts with acetylacetone in the presence of VOII, MnII, FeII, CoII, NiII, and CuII metal salts to give complexes of the type [VO(Ap2ac)2X]X and [M(Ap2ac)2X2] where (Ap2ac) is the ligand formedin situ. The complexes are characterised as distorted octahedral by analyses, conductance, molecular weight, magnetic, electronic and i.r. spectral studies. The i.r. studies reveal that two molecules of aminopyridine are joined by a molecule of acetylacetone through a three carbon atom bridge and that the ligand coordinates through the azomethine and imino nitrogen atoms, whereas pyridine does not take part in coordination. The electronic spectra have been interpreted and tentative assignments are made. In the far i.r. spectra, various metal ligand vibrations are observed and discussed. Attempts to carry out electrophilic substitutions in the complexes failed. 相似文献
4.
A novel series of complexes of the type [M(TML)X2]; where TML is a tetradentate macrocyclic ligand; M = Co(II), Ni(II), Cu(II) or Zn(II); X = Cl−, CH3COO− or NO
3
−
have been synthesized by template condensation of benzil and thiocarbohydrazide in the presence of divalent metal salts in
methanolic medium. The complexes have been characterized with the help of elemental analyses, conductance measurements, molecular
weight determination, magnetic measurements, electronic, NMR, infrared and far infrared spectral studies. Electronic spectra
along with magnetic moments suggest the six coordinate octahedral geometry for these complexes. The low value of molar conductance
indicates them to be non-electrolytes. The biological activities of metal complexes have been tested in vitro against a number of pathogenic bacteria to assess their inhibiting potential. 相似文献
5.
Paul D Melin F Hirtz C Wytko J Ochsenbein P Bonin M Schenk K Maltese P Weiss J 《Inorganic chemistry》2003,42(12):3779-3787
The respective affinities of various imidazole derivatives, imidazole (ImH), 2-methylimidazole (2-MeImH), 2-phenylimidazole (2-PhImH), N-methylimidazole (N-MeIm), 2-methylbenzimidazole (2-MeBzImH), and 4,5-dimethylbenzimidazole (4,5-Me(2)BzImH), for two phenanthroline (Phen) strapped zinc(II) porphyrin receptors porphen-Zn 1-Zn and 2-Zn have been studied. The formation of a supplementary H-bond considerably enhances the affinity of the zinc(II)-porphen receptor for imidazoles unsubstituted on the pyrrolic nitrogen (ImH) versus N-substituted imidazoles such as N-MeIm. The ImHs subset porphen-Zn complexes are formed with association constants up to 4 orders of magnitude superior to those measured either for N-MeIm as substrate or TPP-Zn as receptor. Distal or proximal binding of the substrates was determined by (1)H NMR measurements and titration. In two cases, the very high stability of the inclusion complex enabled the use of 2D NMR techniques. Excellent correlation between solution and solid-state structures has been obtained. A total of six X-ray structures are detailed in this article showing that the evolution of the shape of the zinc(II) receptor is mostly dependent on the steric constraints induced by the substitution on the imidazole. Hindered guests also progressively induce considerable mobility restrictions and severe distortions on the receptor, especially in the case of 2-MeBzImH and 2-PhImH. 相似文献
6.
Structural and optical properties of RF magnetron sputtered aluminum nitride films without external substrate heating 总被引:1,自引:0,他引:1
Atul Vir Singh Sudhir ChandraA.K. Srivastava B.R. ChakrobortyG. Sehgal M.K. DalaiG. Bose 《Applied Surface Science》2011,257(22):9568-9573
We report structural and optical properties of aluminum nitride (AlN) thin films prepared by RF magnetron sputtering. A ceramic AlN target was used to sputter deposit AlN films without external substrate heating in Ar-N2 (1:1) ambient. The X-ray diffraction and high resolution transmission electron microscopy results revealed that the films were preferentially oriented along c-axis. Cross-sectional imaging revealed columnar growth perpendicular to the substrate. The secondary ion mass spectroscopy analysis confirmed that aluminum and nitrogen distribution was uniform within the thickness of the film. The optical band gap of 5.3 eV was evaluated by UV-vis spectroscopy. Photo-luminescence broad band was observed in the range of 420-600 nm with two maxima, centered at 433 nm and 466 nm wavelengths related to the energy states originated during the film growth. A structural property correlation has been carried out to explore the possible application of such important well oriented nano-structured two-dimensional semiconducting objects. 相似文献
7.
8.
Bálint Virág 《Probability Theory and Related Fields》2002,124(1):50-72
Consider the time T
oz
when the random walk on a weighted graph started at the vertex o first hits the vertex set z. We present lower bounds for T
oz
in terms of the volume of z and the graph distance between o and z. The bounds are for expected value and large deviations, and are asymptotically sharp. We deduce rate of escape results for
random walks on infinite graphs of exponential or polynomial growth, and resolve a conjecture of Benjamini and Peres.
Received: 31 October 2000 / Revised version: 5 January 2002 / Published online: 22 August 2002 相似文献
9.
Carbon nanotubes (CNTs) may become ideal reinforcing materials for high-performance nano-composites due their exceptional
properties. Still, much work is needed to be done before the potentials of CNT based composites can be fully realized. The
evaluation of effective material properties of nano-composites is one of many difficult tasks. Simulations using continuum
mechanics approach can play a significant role in the analysis of these composites. In the present work, nonlinear heat conduction
analysis of CNT based composites has been carried out using continuum mechanics approach. Element free Galerkin method has
been applied as a numerical tool. Thermal conductivities of nanotube and polymer matrix are assumed to vary quadratically
with temperature. Picard and quasi-linearization schemes have been utilized to obtain the solution of a system of nonlinear
equations. Cylindrical representative volume element has been used to evaluate the thermal properties of nano-composites.
Present simulations show that the temperature dependent matrix thermal conductivity has a significant effect on the equivalent
thermal conductivity of the composite, whereas temperature dependent nanotube thermal conductivity has a small effect on the
equivalent thermal conductivity of the composite. The results obtained by Picard method have been found almost similar with
those obtained by quasi-linearization approach. 相似文献
10.
Satish K. Pandey Aaydha C. Vinayaka Dharam B. Rishi Praveen Rishi C. Raman Suri 《Analytica chimica acta》2014
Typhoid fever is a life threatening bacterial infection that remains a major global health concern. This continued high burden associated with significant morbidity and mortality rate demands specific and rapid detection technique. This work reports a new sandwich type fluorescence immunoassay format using polymyxin B, a cationic receptor molecule, as a binder agent while anti-Vi antibody served as the capturing agent for specifically detecting Salmonella enterica serovar Typhi. Anti-Vi IgG antibody raised against Vi–BSA conjugate revealed affinity of 7.779 nM−1 signifying immunodominancy of O-acetyls groups in Vi polysaccharide. The detection limit of the developed assay was around 101 cells mL−1 of Vi expressing Salmonella enterica serovar Typhi with a correlation coefficient (R2) equal to 0.97. Positive response obtained for all the tested serovar Typhi clinical isolates as well as the pathogen spiked blood samples recommended specificity and accuracy of Vi antigen as a biomarker during typhoid fever. The intra- and inter-assay precision with Vi spiked samples were satisfactory revealing coefficient of variance (CV%) with a mean of 4.05% and 5.97% respectively. This may be the novel attempt and constructive report on the fluorescence based detection of Vi antigen of serovar Typhi in the epidemic as well as pandemic outbreaks. 相似文献