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The synthesis and X-ray structural determination of 3-O-[(bis-morpholino)phosphinyl]-5,6-O-isopropylidene-l-ascorbate (9) are described. Acid-catalyzed hydrolysis of 9 afforded the 2-O-phosphate 6. Definitive structural proof of 6 is based on a study of the pH profile of its UV spectra as compared with those of ascorbic esters, 2 and 9 (Figs. 1–3). 相似文献
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Dr. Minqiang Jia Dr. Gianpiero Cera Daniele Perrotta Prof. Magda Monari Prof. Marco Bandini 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(32):9875-9878
A careful interplay between the π electrophilicity of a cationic AuI center and the basicity of the corresponding counterion allowed for the chemo‐ and regioselective inter‐ as well as intramolecular de‐aromatization of 2,3‐disubstituted indoles with allenamides. The silver‐free bifunctional Lewis acid/Brønsted base complex [{2,4‐(tBu)2C6H3O}3PAuTFA] assisted the formation of a range of densely functionalized indolenines under mild conditions. 相似文献
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We prove a theorem for the existence of solutions to a variational problem, under assumptions that do not require the convexity of the integrand. 相似文献
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Perrotta RR Winter AH Coldren WH Falvey DE 《Journal of the American Chemical Society》2011,133(39):15553-15558
Calculations at the DFT level predict that benzyl anions with strong π-electron-withdrawing groups in the meta position(s) have low energy diradical or triplet electronic states. Specifically, the 2-(3,5-dinitrophenyl)-1,3-dithiane carbanion is predicted to have nearly degenerate singlet and triplet states at the (U)B3LYP level as a free anion. Its lithium ion pair is predicted to be a ground-state triplet with a substantial (26 kcal/mol) singlet-triplet energy gap. Experiments on this anion using chemical trapping, NMR, and the Evans method strongly suggest that this anion is either a triplet or a ground-state singlet with a very low energy triplet state. 相似文献
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Beneduci A Chidichimo G Tripepi S Perrotta E Cufone F 《Bioelectrochemistry (Amsterdam, Netherlands)》2007,70(2):214-220
In the present study we compared the proliferation behavior, the ultrastructural morphology and the glycolitic metabolism of K562 cells irradiated by low-power wide-band millimeter waves, with those of sham-exposed K562 cells (control), maintained in the same culture conditions. The gigaHertz radiation treatments, performed between 53-78 10(9) Hz, induced a noticeable inhibition of the cell proliferation that could be related to relevant ultrastructural changes. Such effects brought the irradiated cell system to lose the homeostasis and to trigger defense/reparatory mechanisms in order to reestablish a new steady state. (13)C-Nuclear magnetic resonance data on the kinetic of glucose metabolism demonstrated that the irradiated cells enhanced the glycolitic aerobic pathway, indicating that such system need to produce an extra-bioenergy. Most of the ATP synthesized served probably to perform the above processes resulting in a significant decrease of the proliferation rate without significant cell death increment. 相似文献
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Robust methods are needed to fit regression lines when outliers are present. In a clustering framework, outliers can be extreme observations, high leverage points, but also data points which lie among the groups. Outliers are also of paramount importance in the analysis of international trade data, which motivate our work, because they may provide information about anomalies like fraudulent transactions. In this paper we show that robust techniques can fail when a large proportion of non-contaminated observations fall in a small region, which is a likely occurrence in many international trade data sets. In such instances, the effect of a high-density region is so strong that it can override the benefits of trimming and other robust devices. We propose to solve the problem by sampling a much smaller subset of observations which preserves the cluster structure and retains the main outliers of the original data set. This goal is achieved by defining the retention probability of each point as an inverse function of the estimated density function for the whole data set. We motivate our proposal as a thinning operation on a point pattern generated by different components. We then apply robust clustering methods to the thinned data set for the purposes of classification and outlier detection. We show the advantages of our method both in empirical applications to international trade examples and through a simulation study. 相似文献
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Lewis Acid Catalyzed Enantioselective Desymmetrization of Donor–Acceptor meso‐Diaminocyclopropanes 下载免费PDF全文
Daniele Perrotta Ming‐Ming Wang Prof. Dr. Jérôme Waser 《Angewandte Chemie (International ed. in English)》2018,57(18):5120-5123
The first Lewis acid catalyzed enantioselective ring‐opening desymmetrization of a donor–acceptor meso‐diaminocyclopropane is reported. The copper(II)‐catalyzed Friedel–Crafts alkylation of indoles and one pyrrole with an unprecedented meso‐diaminocyclopropane delivered enantioenriched, diastereomerically pure urea products, which are structurally related to natural and synthetic bioactive compounds. The development of a new ligand through the investigation of an underexplored subclass of bis(oxazoline) ligands was essential for achieving high enantioselectivities. 相似文献
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