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The first examples of intramolecular Zr-catalyzed electrophilic alkylation of aryl olefins are disclosed. Substituted carbo- and heterocycles are prepared efficiently and diastereoselectively. 相似文献
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A vinylogous Pictet-Spengler cyclization has been carried out using activated aldehydes, ketones, and alkynes to prepare a variety of substituted hexahydrobenzo[f]isoquinolines. A unique set of conditions was utilized to effect efficient cyclization with acid-sensitive electrophiles. 相似文献
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Juliana S Luz Celso RR Ramos Márcia CT Santos Patricia P Coltri Fernando L Palhano Debora Foguel Nilson IT Zanchin Carla C Oliveira 《BMC biochemistry》2010,11(1):22
Background
The archaeal exosome is formed by a hexameric RNase PH ring and three RNA binding subunits and has been shown to bind and degrade RNA in vitro. Despite extensive studies on the eukaryotic exosome and on the proteins interacting with this complex, little information is yet available on the identification and function of archaeal exosome regulatory factors. 相似文献5.
Cesati RR Dwyer G Jones RC Hayes MP Yalamanchili P Casebier DS 《Organic letters》2007,9(26):5617-5620
Recently developed copper-catalyzed coupling methodology has been applied to the synthesis of amino acid derived enamides. Bond formation proved to be strongly influenced by protection strategy and vinyl iodide substitution while tolerant of limited side chain functionality. Assessment of aminopeptidase activity revealed a preference for (E)-1,2-disubstituted constructs. 相似文献
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Renata Monteiro-Maia Maria B Ortigão-de-Sampaio Rosa T Pinho Luiz RR Castello-Branco 《Journal of immune based therapies and vaccines》2006,4(1):1-6
We hypothesize that the energy strategy of a cell is a key factor for determining how, or if, the immune system interacts
with that cell. Cells have a limited number of metabolic states, in part, depending on the type of fuels the cell consumes.
Cellular fuels include glucose (carbohydrates), lipids (fats), and proteins. We propose that the cell's ability to switch
to, and efficiently use, fat for fuel confers immune privilege. Additionally, because uncoupling proteins are involved in
the fat burning process and reportedly in protection from free radicals, we hypothesize that uncoupling proteins play an important
role in immune privilege. Thus, changes in metabolism (caused by oxidative stresses, fuel availability, age, hormones, radiation,
or drugs) will dictate and initiate changes in immune recognition and in the nature of the immune response. This has profound
implications for controlling the symptoms of autoimmune diseases, for preventing graft rejection, and for targeting tumor
cells for destruction. 相似文献
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A parameterized computational problem is a set of pairs (x, k), where k is a distinguished item called “parameter”. FPT is the class of fixed-parameter tractable problems: for any fixed value of k, they are solvable in time bounded by a polynomial of degree α, where α is a constant not dependent on the parameter. In order to deal with parameterized intractability, Downey and Fellows have introduced a hierarchy of classes W[l] ? W[2] ? ? containing likely intractable parameterized problems, and they have shown that such classes have many natural, complete languages. In this paper we analyze several variations of the halting problem for nondeterministic Turing machines with parameterized time, and we show that its parameterized complexity strongly depends on some resources like the number of tapes, head and internal states, and on the size of the alphabet. Notice that classical polynomial-time complexity fails in distinguishing such features. As byproducts, we show that parameterized complexity is a useful tool for the study of the intrinsic power of some computational models, and we underline the different “computational powers” of some levels of the parameterized hierarchy. 相似文献
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The first enantioselective synthesis of erogorgiaene (1), an inhibitor of mycobacterium tuberculosis, is disclosed. The total synthesis highlights the utility of asymmetric conjugate additions (ACA) of alkylzincs to acyclic alpha,beta-unsaturated ketones catalyzed by peptidic phosphine ligands and (CuOTf)(2).C(6)H(6). Moreover, several critical attributes of this catalytic C-C bond-forming reaction are illustrated in the context of the total synthesis; these include the significance of various structural features of the amino acid-based chiral ligands and the chiral ligand's effectiveness in reactions involving achiral and chiral substrates. In addition, the total synthesis showcases some of the special properties of nonphosphine Ru complex 3 as a highly effective catalyst for olefin cross-metathesis. 相似文献
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VG Adlakha RR Vemuganti 《International Journal of Mathematical Education in Science & Technology》2013,44(5):708-713
In many practical situations scaling the data is necessary to solve linear programs. This note explores the relationships in translating the sensitivity analysis between the original and the scaled problems. 相似文献