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21.
22.
5-Aminofurazano[3,4-d]pyrimidines carrying a variety of substituents at position 7 suffer ring cleavage by either acid or base to give 4-guanidino-3-furazancarboxylic acid (), the esters of which can be recyclised to give the pterin analog 5-amino-7(6H)-furazano[3,4-d]pyrimidinone (9). The pyrimidine ring of (9) is cleaved by hydrolysis, and the furazan ring by hydrogenolysis. 相似文献
23.
Pablo M. Fidelibus Gustavo F. Silbestri María T. Lockhart Sandra D. Mandolesi Alicia B. Chopa Julio C. Podestá 《应用有机金属化学》2007,21(8):682-687
In this paper we describe a three‐step synthesis of aryldi‐ and triboronic acids starting from phenols. Several substituted phenols (I) were converted into the corresponding aryldiethylphosphates (II) in good to excellent yields. The latter, on reaction with sodium trimethylstannide in liquid ammonia, under irradiation, afforded the aryl‐ and heteroarylpoly(trimethylstannyl) derivatives in 65–90% yield. The third step is the reaction of the organotin compounds with borane in THF, which leads to the corresponding arylpolyboronic acids in around 80% yield. In order to confirm their structure, some of the diboronic acids were converted into the corresponding pinacol esters. The results obtained in a study on the synthesis of various terphenyls through double and triple Suzuki couplings catalyzed by palladium acetate between the obtained arylpolyboronic acids and various aryl halides are also reported. These reactions proceeded with an average 65% yield, and also enabled us to confirm the structures of some of the diboronic acids. The structure of the new compounds was determined by 1H, 13C and 119Sn NMR spectroscopy, mass spectrometry and IR spectroscopy. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
24.
Deng H Cobb SL Gee AD Lockhart A Martarello L McGlinchey RP O'Hagan D Onega M 《Chemical communications (Cambridge, England)》2006,(6):652-654
The fluorinase enzyme from S. cattleya is applied as a catalyst for the efficient incorporation of [18F]-fluoride into [18F]-5'-fluoro-5'-deoxyadenosine, [18F]-5'-fluoro-5'-deoxyinosine and [18F]-5-fluoro-5-deoxyribose for positron emission tomography (PET) applications. 相似文献
25.
26.
Certain properties of periodic signals are defined in terms of the zeros and singularities of associated analytic functions of a complex time variablez . This algebraic approach is a generalization of analytic signal theory, and leads to the conception of hybrid modulation as the superposition of twoz -plane zero-singularity (ZS) patterns associated with amplitude- and angle-modulating signals, respectively. It is shown that important spectral properties of the modulated signal, such as band limitation, are explicit in the resultant pattern. Signal design is then interpreted in terms of ZS manipulation and placement. The theory is applied in a unified approach to compatible singlesideband (CSSB) modulation systems. It is shown that two types of proposed CSSB systems give rise to essentially nonband-limited output signals. The relation between conventional and single-sideband (SSB) angle modulation is also discussed in terms of their characteristic ZS patterns. 相似文献
27.
Peter Borwein Richard Lockhart 《Proceedings of the American Mathematical Society》2001,129(5):1463-1472
The results of this paper concern the expected norm of random polynomials on the boundary of the unit disc (equivalently of random trigonometric polynomials on the interval ). Specifically, for a random polynomial
let
Assume the random variables , are independent and identically distributed, have mean 0, variance equal to 1 and, if 2$">, a finite moment . Then
and
as .
In particular if the polynomials in question have coefficients in the set (a much studied class of polynomials), then we can compute the expected norms of the polynomials and their derivatives
and
This complements results of Fielding in the case, Newman and Byrnes in the case, and Littlewood et al. in the case.
28.
We study the behaviour of the glued trees algorithm described by Childs et al. in [1] under decoherence. We consider a discrete time reformulation of the continuous time quantum walk protocol and apply a phase damping channel to the coin state, investigating the effect of such a mechanism on the probability of the walker appearing on the target vertex of the graph. We pay particular attention to any potential advantage coming from the use of weak decoherence for the spreading of the walk across the glued trees graph. 相似文献
29.
30.
Lo Fiego MJ Silbestri GF Chopa AB Lockhart MT 《The Journal of organic chemistry》2011,76(6):1707-1714
Bulky arylstannanes and bulky aroyl chlorides are good reaction partners for the synthesis of two-, three-, and even four-ortho-substituted benzophenones, in good to excellent isolated yields (47-91%). Three simple and direct routes, with differential advantages, are proposed: (i) a catalyst-free protocol, in o-dichlorobenzene (ODCB) at 180 °C; (ii) a room temperature protocol, using AlCl(3) (0.5 equiv), in dichloromethane (DCM); and (iii) a solvent-free, indium-promoted procedure. A radical mechanism is proposed for the indium-mediated reactions. 相似文献