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161.
Daniel Bellu Hanspeter Fischer Hans Greuter Pierre Martin 《Helvetica chimica acta》1978,61(5):1784-1813
Syntheses of Moniliformin, a Mycotoxine with a Cyclobutenedione Structure Six different routes to 3-hydroxy-3-cyclobutene-1, 2-dione ( 4 ), the free acid of the mycotoxine Moniliformin (=alkali salt of 4 ) are described. A common feature of all pathways is the synthesis of cyclobutanes having the oxidation level 6. Moniliformin precursors which are easily transformed to 4 by acid catalysed hydrolysis include [2+2]-cycloadducts of ketene with tetraalkoxy-olefins, 3,4,4-trialkoxycyclobutenes, derivatives of polyfluorinated cyclobutenes, the brominated [2+2]-cycloadduct of ethyl vinyl ether and dichloroketene, tetrabromocyclobutanone, [2+2]-photocycloadducts of dichlorovinylenecarbonate with dichloroethylenes, and the dimer of chloroketene. The most convenient synthesis via the [2+2]-cycloadduct of tetraethoxyethylene and ketene ( 14b ) is reported in detail and produces 4 in four simple steps in 57% overall yield. In addition, two new syntheses of squaric acid ( 56 ) are described. 相似文献
162.
The [2.2.2]hericene ( 6 ), a bicyclo[2.2.2]octane bearing three exocyclic s-cis-butadiene units has been prepared in eight steps from coumalic acid and maleic anhydride. The hexaene 6 adds successively three mol-equiv. of strong dienophiles such as ethylenetetracarbonitrile (TCE) and dimethyl acetylenedicarboxylate (DMAD) giving the corresponding monoadducts 17 and 20 (k1), bis-adducts 18 and 21 (k2) and tris-adducts 19 and 22 (k3), respectively. The rate constant ratio k1/k2 is small as in the case of the cycloadditions of 2,3,5,6-tetramethylidene-bicyclo [2.2.2]octane ( 3 ) giving the corresponding monoadducts 23 and 27 (k1) and bis-adducts 25 and 29 (k2) with TCE and DMAD, respectively. Constrastingly, the rate constant ratio k2/k3 is relatively large as the rate constant ratio k1/k2 of the Diels-Alder additions for 5,6,7,8-tetramethylidenebicyclo [2.2.2]oct-2-ene ( 4 ) giving the corresponding monoadducts 24 and 28 (k1) and bis-adducts 26 and 30 (k2). The following second-order rate constants (toluene, 25°) and activation parameters were obtained for the TCE additions: 3 +TCE→ 23 : k1 = 0.591±0.012 mol?1·l·s?1, ΔH≠=10.6±0.4 kcal/mol, and ΔS≠ = ?24.0±1.4 cal/mol·K (e.u.); 23 +TCE→ 25 : k2=0.034±0.0010 mol?1·l·s?1, ΔH≠ = 10.6±0.6 kcal/mol, and ΔS≠ = ?29.7±2.0 e.u.; 4 +TCE→ 26 : k1 = 0.172±0.035 mol?1·l·s?1, ΔH≠ 11.3±0.8 kcal/mol, and ΔS≠ = ?24.0±2.8 e.u.; 24 +TCE→ 26 : k2 = (6.1±0.2)·10?4 mol?1·l·s?1, ΔH≠ = 13.0±0.3 kcal/mol, and ΔS≠ = ?29.5±0.8 e.u.; 6 +TCE→ 17 : k1 = 0.136±0.002 mol?1·l·s?1, ΔH≠ = 11.3±0.2 kcal/mol, and ΔS≠ = ?24.5±0.8 e.u.; 17 +TCE→ 18 : k2 = 0.0156±0.0003 mol?1·l·s?1, ΔH≠ = 10.9±0.5 kcal/mol, and ΔS≠ = ?30.1 ± 1.5 e.u.; 18 +TCE→ 19 : k3=(5±0.2) · 10?5 mol?1 mol?1 ·l·s?1, ΔH≠ = 15±3 kcal/mol, and ΔS≠ = ?28 ± 8 e.u. The following rate constants were evaluated for the DMAD additions (CD2Cl2, 30°): 6 +DMAD→ 20 : k1 = (10±1)·10?4 mol?1 · l·s?1; 20 +DMAD→ 21 : k2 = (6.5±0.1) · 10?4 mol?1 ·l·?1; 21 +DMAD→ 22 : k3 = (1.0±0.1) · 10?4 mol?1 ·l·s?1. The reactions giving the barrelene derivatives 19, 22, 26 and 30 are slower than those leading to adducts that are not barrelenes. The former are estimated less exothermic than the latter. It is proposed that the Diels-Alder reactivity of exocyclic s-cis-butadienes grafted onto bicycle [2.2.1]heptanes and bicyclo [2.2.2]octanes that are modified by remote substitution of the bicyclic skeletons can be affected by changes inthe exothermicity of the cycloadditions, in agreement with the Dimroth and Bell-Evans-Polanyi principle. Force-field calculations (MMPI 1) of 3, 4, 6 and related exocyclic s-cis-butadienes as a moiety of bicyclo [2.2.2]octane suggested single minimum energy hypersurfaces for these systems (eclipsed conformations, planar dienes). Their flexibility decreases with the degree of unsaturation of the bicyclic skeleton. The effect of an endocyclic double bond is larger than that of an exocyclic diene moiety. 相似文献
163.
In four synthetic steps, (+)- and (–)-methyl 8-epinonactate ((+)- and (–)− 4 ) have been derived from (+)- and (–)-7-oxabicyclo[2.2.1]heptan-2-one ((+)- and (–)− 9 ), respectively. The (+)- and (–)-methyl nonactate ((+)- and (–)− 3 ) were obtained from (+)- and (–)− 4 , respectively, by Mitsunobu displacement reactions. Optical resolution of (±)− 9 via chromatographic separation of the corresponding N-methyl-S-alkyl-S-phenylsulfoximides 24 and 25 yielded the starting materials (+)- and (–)− 9 , respectively. 相似文献
164.
Christian Miquel Pierre Pigache Benoit Rigo Nicolas Kolocouris 《Journal of heterocyclic chemistry》1980,17(7):1447-1453
Starting from the readily available 5-oxo-2-carboxypyrrolidine, methylene-bis-(N-5-oxo-2-carboxypyrrolidine) was prepared and transformed into a diamine, then into two isomeric diols, which cyclised into one ether. The meso configuration has been assigned for this ether. The reduction of both diols and ether was complete and gave rise to methylene-bis-N-pyrrolidine. 相似文献
165.
Carolina L. da Silva José O. Del Ciampo Fábia C. Rossetti Maria V. L. B. Bentley Maria B. R. Pierre 《Photochemistry and photobiology》2013,89(5):1176-1184
We report the development of d , l lactic co‐glycolic acid) (PLGA)‐based nanoparticles (NPs) for topical delivery of protoporphyrin IX (PpIX), a photosensitizer (PS), in treatments like photodynamic therapy (PDT) of skin cancers. PpIX‐NPs were obtained in ~75.0% yield, encapsulation efficiency of 67.7%, drug content of 50.3 μg mg?1, average diameter of 290 nm maintained up to 30 days and a zeta potential of 32.3 mV. Sustained in vitro release of PpIX through artificial membranes following Higuchi kinetics was kept up to 10 days. In vitro retentions of PpIX both in stratum corneum (SC) and epidermis + dermis ([EP + D]) were higher from NPs (23.0 and 10.0 times, respectively) compared to control solutions at all times. Quantification of PpIX by extraction, after in vivo skin application of NPs‐PpIX on hairless mice, showed higher retention of the PS both in SC and in [EP + D] (3.0 and 2.0 times, respectively) compared to control solutions. Taken together, the results indicate that NPs are suitable for PpIX encapsulation showing minimal permeation through the skin and a localized effect, characteristics of a potential and promising delivery system for PDT‐associated treatments of skin cancers, photodiagnosis and their off‐label uses. 相似文献
166.
Pierre Escalé Laurent Rubatat Laurent Billon Maud Save 《European Polymer Journal》2012,48(6):1001-1025
Since its introduction in 1994, the preparation of ordered porous polymer films by the breath figure (BF) method has received a considerable interest. The so-called “honeycomb” (HC) films exhibit a hexagonal array of micrometric pores obtained by water droplet condensation during the fast solvent evaporation performed under a humid flow. The main focus of this feature article is to describe the recent advances in the design of honeycomb polymer films by the BF process. We first review the recent studies related to the honeycomb film formation through the exploration of different parameters such as the relative humidity, the polymer concentration, the drying rate, the substrate or the role of interfacial tension. The influence of the architecture and microstructure of the polymer is examined through examples. In this contribution, a special attention is given to the recent articles focused on the preparation of elaborate functional honeycomb-structured polymer films obtained via the simple BF method. In this context, we review the preparation of hierarchical HC films showing either sub- or super-structure, the formation of hybrid HC films by self-assembly of nanoparticles or in situ generation of the inorganic matter, the fluorescence in HC films introduced either by a fluorescent polymer or by fluorescent chemical groups, the elaboration of biomaterials from HC films decorated by glycopolymer and/or showing sensing ability and finally the design of functional polymeric surfaces with either stimuli-responsive or superhydrophobic properties. 相似文献
167.
168.
SiO2–Al2O3 aerogels and xerogels with a Si to Al molar ratio r
Si/Al varying from 0.25 to 20, were made by sol-gel process in acidic conditions at pH 2 and respectively dried by the CO2 supercritical method and by solvent evaporation. The Al precursor was also chelated with ethylacetoacetate, which made it possible to study the structure and texture of such gels in conditions favorable to the formation of mixed Al–O–Si bonds. Nitrogen adsorption isotherms according to the Brunauer, Emmett and Teller method (BET), 27Al magic angle spinning nuclear magnetic resonance (27Al MAS-NMR), Fourier Transformed Infrared Spectroscopy (FTIR) and Infrared absorbance spectra after Temperature Programmed Desorption (TPD) of pyridine, showed that the Si–O infrared asymmetric stretching vibration and the Bronsted acidity relative to the Lewis acidity, depended on the ratio of AlIV to Si atoms. 相似文献
169.
Thamina Akther Md.Monarul Islam Taisuke Matsumoto Junji Tanaka Pierre Thuéry Carl Redshaw Takehiko Yamato 《Tetrahedron》2018,74(2):329-335
The reductive coupling reaction of 1,4-bis(3-acetyl-5-tert-butyl-2-methoxyphenyl)butane 3 was carried out using TiCl4-Zn in pyridine followed by a McMurry coupling reaction to afford the compounds anti and syn 1,2-dimethyl[2.4]MCP-1-ene 4. Bromination of 4 with BTMA-Br3 in dry CH2Cl2 afforded the interesting compound 1,2-bis-(bromomethyl)-5,15-di-tert-butyl-8,18-dimethoxy[2.4]MCP-1-ene 6 and consecutive debromination with Zn and AcOH in CH2Cl2 solution afforded the stable solid 5,15-di-tert-butyl-8,18-dimethoxy-1,2-dimethylene[2.4]MCP 7 in 89% yield. Compound 7 was conveniently employed in a Diels–Alder reaction with dimethyl acetylenedicarboxylate (DMAD) to provide 2-(3′,6′-dihydrobenzo)-5,15-di-tert-butyl-8,18-dimethoxy[2.4]MCP-4′,5′-dimethylcarboxylate 8 in good yield. Diels–Alder adduct 8 was converted into a novel and inherently chiral areno-bridged compound [2.4]MCP 9 by aromatization. The chirality of the two conformers was characterized by circular dichroism (CD) spectra of the separated enantiomer which are perfect mirror images of each other. 相似文献
170.
Glycosyl‐Substituted Dicarboxylates as Detergents for the Extraction,Overstabilization, and Crystallization of Membrane Proteins 下载免费PDF全文
Dr. Kim‐Anh Nguyen Dr. Marine Peuchmaur Sandrine Magnard Dr. Romain Haudecoeur Dr. Cédric Boyère Saravanan Mounien Ikram Benammar Veronica Zampieri Dr. Sébastien Igonet Dr. Vincent Chaptal Dr. Anass Jawhari Prof. Ahcène Boumendjel Dr. Pierre Falson 《Angewandte Chemie (International ed. in English)》2018,57(11):2948-2952
To tackle the problems associated with membrane protein (MP) instability in detergent solutions, we designed a series of glycosyl‐substituted dicarboxylate detergents (DCODs) in which we optimized the polar head to clamp the membrane domain by including, on one side, two carboxyl groups that form salt bridges with basic residues abundant at the membrane–cytoplasm interface of MPs and, on the other side, a sugar to form hydrogen bonds. Upon extraction, the DCODs 8 b , 8 c , and 9 b preserved the ATPase function of BmrA, an ATP‐binding cassette pump, much more efficiently than reference or recently designed detergents. The DCODs 8 a , 8 b , 8 f , 9 a , and 9 b induced thermal shifts of 20 to 29 °C for BmrA and of 13 to 21 °C for the native version of the G‐protein‐coupled adenosine receptor A2AR. Compounds 8 f and 8 g improved the diffraction resolution of BmrA crystals from 6 to 4 Å. DCODs are therefore considered to be promising and powerful tools for the structural biology of MPs. 相似文献