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Marcela Dvorakova Marie Pribylova Radek Pohl Marie E. Migaud Tomas Vanek 《Tetrahedron》2012,68(33):6701-6711
A migration of methyloxycarbonyl group from secondary to primary hydroxyl was observed in furanosides (ribosides and xylosides) under usual desilylation conditions using tetrabutylammonium fluoride. The migration was studied further on several alkyloxycarbonyl furanosides under either basic or acidic conditions. As follows from 13C labelling experiments and product distribution, the migration in xylosides, proceeds intramolecularly via six-membered cyclic carbonate, whereas in ribosides, the migration is intermolecular. Acidic conditions prevented the migration in ribosides whereas the migration in xylosides was circumvented under neutral conditions. 相似文献
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Multistage Interconnection Networks (MINs) are network systems providing fast and efficient communications at a reasonable cost. A gamma network is a specific class of MINs, which provides redundant paths in the system. In a gamma network, information from source nodes is transmitted through a specific set of routes to destination nodes. Reliability of an MIN is used as a measure of system’s ability to transform information from input to output devices. Due to the complexity of network configuration and availability of redundant paths, reliability bounds to estimate the exact reliability of a gamma network is proposed. A numerical example of an 8 × 8 gamma network is presented to demonstrate the accuracy of the reliability bounds. When the lower bound reliability provides sufficient assurance that the system will be operational at some specified time and closely approximates the exact reliability, then no further effort for obtaining the exact reliability expression is necessary. 相似文献
36.
-5-Aryl-1-[2-(phosphonomethoxy)ethyl]uracils were prepared via Pd-catalyzed Suzuki-Miyaura coupling reaction of the appropriate 5-bromouracil derivative with a series of arylboronic acids followed by deprotection. These compounds were designed as potential multisubstrate inhibitors of thymidine phosphorylase based on an assumption that the potential hydrophobic effect of the aryl groups might modify the inhibitory effect towards this enzyme and they may also demonstrate cytostatic activity. 相似文献
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Lalit Giri Arun Kumar Jugran Amit Bahukhandi Praveen Dhyani Indra D. Bhatt Ranbeer Singh Rawal Shyamal Kumar Nandi Uppeandra Dhar 《Applied biochemistry and biotechnology》2017,181(1):267-282
Habenaria edgeworthii Hook. f. ex Collett is an important terrestrial orchid used in different Ayurvedic formulations. In the present study, variations among morphological, phytochemical and molecular markers were assessed. A significant difference was observed among populations using morphological traits. Inter-simple sequence repeat (ISSR) data revealed lower genetic diversity at population level (He = 0.207) as compared to species level (He = 0.334). Analysis of molecular variance (AMOVA) indicates 74 % variation among populations and 26 % within population. Tuber extracts showed significantly (p < 0.05) higher total phenolics and flavonoids among the populations. Antioxidant activity determined by 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging, 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging and ferric reducing antioxidant power (FRAP) assays exhibited considerable antioxidant potential. Furthermore, the associations between molecular and morphological and phytochemical attributes were studied using multiple regression analysis (MRA). Several ISSR fragments were associated with some morphological and phytochemical traits. These ISSR fragments can be useful for breeding programme of the species when no other genetic information, such as linkage maps and quantitative trait loci, is available. 相似文献
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The mechanism of the decomposition of acryloylcarbamates 7a–b yielding highly reactive isocyanates 3a–b was proposed based on NMR measurements and quantum chemical calculations. A good agreement between the experimental kinetic data and DFT calculations allowed us to demonstrate that the stability of 7a–d depends on the presence of methyl in the acryloyl moiety and the position of the nitro group in the nitrophenolic part of the molecule. Furthermore, the reactivity of 7a–d with weakly nucleophilic and sterically hindered 2,4,6‐tri‐tert‐butylaniline was explored by 1H NMR demonstrating the usefulness of reagents 7a–d offering access to a variety of 1‐N‐substituted uracils and thymines with potentially interesting biological properties. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
39.
Dr. Pavlína Košinová Dr. Radek Gažák Prof. Jean‐Luc Duroux Prof. Roberto Lazzaroni Prof. Vladimír Křen Prof. Xavier Assfeld Dr. Patrick Trouillas 《Chemphyschem》2011,12(6):1135-1142
Natural polyphenols are known to be oxidized by free radicals, which partially explains the antioxidant properties of a number of these compounds. This oxidation may also be used to synthesise new compounds of biological interest, for example, dimers. The present theoretical study describes the existing experimental evidence showing that silybin and dehydrosilybin [natural polyphenols isolated from milk thistle (Silybum marianum)] form dimers regioselectively. Based on DFT calculations, thermodynamic and kinetic values were computed in order to better understand the physicochemical behaviour of these dimerisation processes. Calculations showed that after H‐atom transfer (from polyphenol to radical), dimerisation could proceed in two steps: 1) bond formation and, when possible, 2) tautomerisation reorganisation. The former step is the limiting step, while the latter is crucial for the process to be thermodynamically favourable (ΔG<0). If this rearrangement is impossible then dimerisation is not feasible, or at least becomes a minor process (e.g., dehydrosilybin dimerisation after H‐atom abstraction from the 3‐OH group). This explains the regioselectivity of polyphenol dimerisation. 相似文献
40.
Substituting CF2 for O4′ in Components of Nucleic Acids: Towards Systems with Reduced Propensity to Form Abasic Lesions
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Dr. Yevgen P. Yurenko Dr. Jan Novotný Prof. Dr. Vladimir Sklenář Prof. Dr. Radek Marek 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(49):17933-17943
Intrinsic structural features and energetics of nucleotides containing variously fluorinated sugars as potential building blocks of DNA duplexes and quadruplexes are explored systematically using the modern methods of density functional theory (DFT) and quantum chemical topology (QCT). Our results suggest that fluorination at the 2′‐β or 2′‐α,β positions somewhat stabilizes in vacuo the AI relative to the BI conformations. In contrast, substitution of the CF2 group for the O4′ atom (O4′‐CF2 modification) leads to a preference of the BI relative to AI DNA‐like conformers. All the studied modifications result in a noticeable increase in the stability of the glycosidic bond [estimated by the relaxed force constants (RFC) approach], with particularly encouraging results for the O4′‐CF2 derivative. Consequently, the O4′‐CF2 modified systems are suggested and explored as promising scaffolds for the development of duplex and quadruplex structures with reduced propensity to form abasic lesions and to undergo DNA damage. 相似文献