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11.
Synthesis of Nonactin. The macrotetrolide antibiotic nonactin (I), containing four units of a C10 hydroxy acid, has been synthesized starting from two adequately protected derivatives (III and IV) of nonactic acid (II). The 32-membered ring of the macrotetrolide is built up by a sequence of condensation and deprotection steps leading first to a product with two, and subsequently to one with four nonactic acid residues (VIII) which is then cyclized in the presence of Ag+-ions. Two reactions forming ester bonds have been developed to condense the hydroxy acids and to effect the final cyclization. In one the activation of the carboxyl group is achieved by conversion into the mixed anhydride with 2,4,6-trimethylbenzene sulfonyl chloride in pyridine. In the other the Ag+-ion induced reaction of a S-(2-pyridyl) hydroxy carbothioate is used to form the corresponding macrocyclic lactone. In the case of nonactin the ring closure is promoted by the coordinating effect of Ag+-ions present in the reaction mixture. 相似文献
12.
Synthesis of N‐(1H‐imidazoline‐2‐yl)‐1H‐benzimidazol‐2‐amine was carried out under microwave irradiation (MWI) conditions. Dynamic 1H NMR investigation of N‐(1H‐imidazoline‐2‐yl)‐1H‐benzimidazol‐2‐amine compound was reported at temperature range of 223–333 K in DMF‐d7. Some physical parameters, such as coalescence temperature (Tc), the free energy of activation (ΔG??) and rate constant (k) values were calculated from its 1H NMR spectra at various temperatures. Electrochemical feature of this compound was investigated by cyclic (CV) and square wave voltammetry (SWV). 相似文献
13.
Poolman HR Boersma DJ Harvey M Higinbotham DW Passchier I Six E Alarcon R van Amersfoort PW Bauer TS Boer Rookhuizen H van Den Brand JF van Buuren LD Bulten HJ Ent R Ferro-Luzzi M Geurts DG Heimberg P de Jager CW Klimin P Koop I Kroes F van Der Laan J Luijckx G Lysenko A Militsyn B Nesterenko I 《Physical review letters》2000,84(17):3855-3858
We report on first measurements with polarized electrons stored in a medium-energy ring and with a polarized internal target. Polarized electrons were injected at 442 MeV (653 MeV), and a partial (full) Siberian snake was employed to preserve the polarization. Longitudinal polarization at the interaction point and polarization lifetime of the stored electrons were determined with laser backscattering. Spin observables were measured for electrodisintegration of polarized 3He, with simultaneous detection of scattered electrons, protons, neutrons, deuterons, and 3He nuclei, over a large phase space. 相似文献
14.
Mario Servi 《Annali dell'Universita di Ferrara》1970,15(1):57-92
Riassunto SiaK una categoria con prodotti finiti e siaA un oggetto diA. Un'operazione n-adica suA è un morfismoA
n→A; unastruttura algebrica suA è una famiglia di operazioni suA edA con una tale struttura si dirà un'algebra in
K. Con queste definizioni, è possibile studiare alcuni problemi di algebra universale riferiti alle algebre inK.
Lavoro eseguito nell'ambito dell'attività dei Gruppi di Ricerca Matematici del C.N.R., nell'anno 1969.
Nota diMario Servi a Parma—V.le La Grola, 29.—43100 Parma. 相似文献
Summary LetK be a category with finite products and a null object and letAεOb K Ann-ary operation on A is any morphismA n→A and analgebra in K is an object together with a family of operations on it. We study some problems concerning algebras inK.
Lavoro eseguito nell'ambito dell'attività dei Gruppi di Ricerca Matematici del C.N.R., nell'anno 1969.
Nota diMario Servi a Parma—V.le La Grola, 29.—43100 Parma. 相似文献
15.
We address the problem of assigning probabilities at discrete time instants for routing toll-free calls to a given set of call centers to minimize a weighted sum of transmission costs and load variability at the call centers during the next time interval.We model the problem as a tripartite graph and decompose the finding of an optimal probability assignment in the graph into the following problems: (i) estimating the true arrival rates at the nodes for the last time period; (ii) computing routing probabilities assuming that the estimates are correct. We use a simple approach for arrival rate estimation and solve the routing probability assignment by formulating it as a convex quadratic program and using the affine scaling algorithm to obtain an optimal solution.We further address a practical variant of the problem that involves changing routing probabilities associated with k nodes in the graph, where k is a prespecified number, to minimize the objective function. This involves deciding which k nodes to select for changing probabilities and determining the optimal value of the probabilities. We solve this problem using a heuristic that ranks all subsets of k nodes using gradient information around a given probability assignment.The routing model and the heuristic are evaluated for speed of computation of optimal probabilities and load balancing performance using a Monte Carlo simulation. Empirical results for load balancing are presented for a tripartite graph with 99 nodes and 17 call center gates. 相似文献
16.
An efficient synthesis of 2‐arylamino‐2‐imidazolines from dimethyl N‐aryldithioimidocarbonates and ethylenediamine on solid support under microwave irradiation has been developed. The reaction time has been reduced from hours to minutes with improved yields as compared to conventional heating. Their piperidin‐4‐ylmethyl and morpholin‐4‐ylmethyl derivatives were synthesized by treatment with formaldehyde and piperidine or morpholine. © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:142–222, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20081 相似文献
17.
This paper develops a real time algorithm which identifies times of emotional discontinuity as reflected in social media. The paper formulates the optimization problem to solve, develops an algorithm to solve it using dynamic programming, and illustrates the new method by analyzing mood shifts reflected in 380,000 Twitter messages related to one of the world’s most popular soccer teams, Manchester United, during their 2011–12 season. 相似文献
18.
Canan Kazak Veysel T. Yilmaz Suleyman Servi Murat Koca Frank W. Heinemann 《Acta Crystallographica. Section C, Structural Chemistry》2005,61(6):o348-o350
The title compounds, 1,3‐dibenzoylimidazolidine‐2‐thione, C17H14N2O2S, (I), and 1,3‐dibenzoyl‐3,4,5,6‐tetrahydropyrimidine‐2(1H)‐thione, C18H16N2O2S, (II), were obtained from the reactions of imidazolidine‐2‐thione and 1,4,5,6‐tetrahydropyrimidine‐2‐thiol, respectively, with benzoyl chloride. Compounds (I) and (II) contain, respectively, imidazolidinethione [C=S = 1.6509 (14) Å] and pyrimidinethione [C=S = 1.6918 (19) Å] moieties bonded to two benzoyl rings. The molecules of (I) exhibit C2 symmetry, the C=S bond lying along the twofold rotation axis, while the molecules of (II) have mirror symmetry (Cs). The imidazolidine ring in (I) is essentially planar, while the pyrimidine ring in (II) adopts a boat conformation. Molecules of (I) are linked by weak intermolecular C—H⋯O interactions, while molecules of (II) are held together by van der Waals interactions. 相似文献
19.
Çiǧdem Yüksektepe Nezihe Çalişkan Murat Genç Süleyman Servi 《Crystallography Reports》2010,55(7):1188-1193
The titled compound (1), has been synthesized and characterized by IR and 1H-NMR spectroscopy, and single crystal X-ray diffraction. The compound crystallizes in the triclinic space group P-1. The crystal structure is stabilized by C-H…π and aromatic π-π interactions. There are also intramolecular N-H…N and C-H…N
hydrogen bonds in the molecule. The use of quantum chemical calculations to characterise and optimise the choice of material
is illustrated by ab initio treatments. Vibrational frequencies and LUMO-HOMO energy difference of 1 have also been investigated by Density functional theory (DFT) and Hartree-Fock (HF) calculations. Calculated frequencies
are in good agreement with the corresponding experimental data. 相似文献
20.
Giovanni Fronza Claudio Fuganti Domenica Pizzi Stefano Servi 《Journal of carbohydrate chemistry》2013,32(2-3):317-332
ABSTRACT 4S-cis-2, 2, 5-Trimethyl-l, 3-dioxolane-4-carboxaldehyde (1) undergoes stereoselective nucleophilic addition with different vinyl metals. Allylic alcohols thus obtained are possible intermediates in the synthesis of deoxysugars. By ? reiterative 1 C extension cycle, 6-deoxyhexoses can be obtained. 相似文献