Exo

Distribution by Scientific Domains
Distribution within Chemistry


Selected Abstracts


Molecular Analysis of Brassinosteroid Action

PLANT BIOLOGY, Issue 3 2006
C. Müssig
Abstract: Brassinosteroids (BRs) are steroidal plant hormones with important regulatory roles in various physiological processes, including growth, xylem differentiation, disease resistance, and stress tolerance. Several components of the BR signal transduction pathway have been identified. The extracellular domains of receptor kinases such as BRI1 perceive BRs and transduce the signal via intracellular kinase domains. Within the cell further kinases and phosphatases determine the phosphorylation status of transcription factors such as BES1 and BZR1. These factors mediate major BR effects. Studies of BR-regulated genes shed light on the molecular mode of BR action. Genes encoding cell-wall-modifying enzymes, enzymes of the BR biosynthetic pathway, transcription factors, and proteins involved in primary and secondary metabolism are subject to BR-regulation. Gene expression data also point at interactions with other phytohormones and a role of BR in stress responses. This article gives a survey of the BR-signaling pathway. Two BR-responsive genes, OPR3 and EXO, are described in detail. [source]


Non-LTE model atmospheres for supersoft X-ray sources

ASTRONOMISCHE NACHRICHTEN, Issue 2 2010
T. Rauch
Abstract In the last decade, X-ray observations of hot stellar objects became available with unprecedented resolution and S/N ratio. For an adequate interpretation, fully metal-line blanketed Non-LTE model-atmospheres are necessary. The Tübingen Non-LTE Model Atmosphere Package (TMAP) can calculate such model atmospheres at a high level of sophistication. Although TMAP is not especially designed for the calculation of spectral energy distributions (SEDs) at extreme photospheric parameters, it can be employed for the spectral analysis ofburst spectra of novae like V4743 Sgr or line identifications in observations of neutron stars with low magnetic fields in low-mass X-ray binaries (LMXBs) like EXO 0748-676 (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Crystallization of selenomethionyl exo-,-1,3-galactanase from the basidiomycete Phanerochaete chrysosporium

ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 12 2009
Takuya Ishida
Exo-,-1,3-galactanase from Phanerochaete chrysosporium (Pc1,3Gal43A) consists of a glycoside hydrolase family 43 catalytic domain and a substrate-binding domain that belongs to carbohydrate-binding module family 35. It catalyzes the hydrolysis of ,-1,3-galactan, which is the backbone of the arabinogalactan proteins; the C-terminal carbohydrate-binding module family 35 domain increases the local concentration of the enzyme around ,-1,3-galactan by its high affinity for the substrate. To enable phase determination using the multiwavelength anomalous dispersion method, selenomethionyl Pc1,3Gal43A was crystallized at 298,K using the hanging-drop vapour-diffusion method. The presence of selenium in the crystals was confirmed from the X-ray absorption spectrum. The crystals belonged to space group P21 and diffracted to 1.8,Å resolution. [source]


Reversible Control of Exo - and Endo -Budding Transitions in a Photosensitive Lipid Membrane

CHEMBIOCHEM, Issue 2 2009
Ken-ichi Ishii
Abstract We have developed a method for the photomanipulation of lipid membrane morphology in which the shape of a vesicle can be switched by light through the use of a synthetic photosensitive amphiphile containing an azobenzene unit (KAON12). We prepared cell-sized liposomes from KAON12 and 1,2-dioleoyl- sn -glycero-3-phosphocholine (DOPC) and conducted real-time observations of vesicular transformation in the photosensitive liposome by phase-contrast microscopy. Budding transitions,either budding toward the centre of the liposome (endo -bud) or budding out of the liposome (exo- bud),could be controlled by light. We discuss the mechanism of this transformation in terms of the change in the effective membrane surface area due to photoisomerization of the constituent molecules. [source]


Exo- and Endocyclic Oxazolinyl,Phosphane Palladium Complexes: Catalytic Behavior in Allylic Alkylation Processes.

CHEMINFORM, Issue 42 2004
Delphine Franco
Abstract For Abstract see ChemInform Abstract in Full Text. [source]


Anaerobic transformation of compounds of technical toxaphene.

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 11 2003

Abstract Technical toxaphene (Melipax) and the single compounds of technical toxaphene (CTTs) 2,2,5- endo, 6- exo, 8,8,9,10- octachlorobornane (B8-806), 2,2,5- endo, 6- exo, 8,9,9,10-octachlorobornane (B8-809), 2,2,5,5,8,9,9,10,10-nonachlorobornane (B9- 1025), 2- endo, 3- exo, 5- endo, 6- exo, 8,8,9,10,10-nonochlorobornane (B9-1679), 2- endo, 3- exo, 5- endo, 6- exo, 8,9,10,10-octachlorobornane (B8-1414), 2- endo, 3- exo, 5- endo, 6- exo, 8,8,9,10-octachlorobornane (B8-1412), and 2- exo, 3- endo, 5- exo, 9,9,10,10-heptachlorobornane (B7-1453) were treated with suspensions of the anaerobic bacterium Dehalospirillum multivorans. After 7 d, more than 50% of technical toxaphene was transformed, and the relative amount of early eluting CTTs increased. After 16 d, only 2- exo, 3- endo, 6- exo, 8,9,10-hexachlorobornane (B6-923), 2- endo, 3- exo, 5- endo, 6- exo, 8,9,10-heptachlorobornane (B7-1001), and a few minor penta- and hexachloro-CTTs were detected in the samples. The result of the transformation was comparable with observations in naturally contaminated sediments and soil. However, the performance with D. multivorans was more simple and reproducible, as well as faster, than use of soil, sediment, or anaerobic sewage sludge. In agreement with reports in the literature, reductive dechlorination at geminal chlorine atoms (gem -Cls) was found to be the major CTT transformation pathway. Experiments conducted with CTTs and gem -Cls at both primary and secondary carbons clarified that the initial Cl -> H substitution takes place at the secondary carbon C2. Furthermore, the 2- endo -Cl position was preferably substituted with hydrogen. In the case of B8-806, the dechlorination at the secondary carbon C2 was approximately 20-fold faster than the subsequent, slow reduction at the primary carbon C8. The three different formerly unknown heptachloro-CTTs, 2- exo, 3- endo, 6- exo, 8,9,9,10-heptachlorobornane (B7-1473), 2- exo, 3- endo, 6- endo, 8,9,9,10-hepatchlorobornane (B7-1461), and 2- exo, 3- endo, 6- exo, 8,8,9,10-heptachlorobornane (B7-1470) were found as intermediates of the B8-806/809 transformation. Treatment of B9-1679 with D. multivorans indicated that gem -Cls on the bridge (C8 and C9) are dechlorinated faster than gem -Cls on the bridgehead (C10). [source]


The Effect of Surface Area and Crystal Structure on the Catalytic Efficiency of Iron(III) Oxide Nanoparticles in Hydrogen Peroxide Decomposition

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 16 2010
Cenek Gregor
Abstract Iron(II) oxalate dihydrate has been used as a readily decomposable substance for the controlled synthesis of nanosized iron(III) oxides. The polymorphous composition, particle size and surface area of these iron oxide nanoparticles were controlled by varying the reaction temperature between 185 and 500 °C. As-prepared samples were characterized by XRD, low-temperature and in-field Mössbauer spectroscopy, BET surface area and the TEM technique. They were also tested as heterogeneous catalysts in hydrogen peroxide decomposition. At the selected temperatures, the formed nanomaterials did not contain any traces of amorphous phase, which is known to considerably reduce the catalytic efficiency of iron(III) oxide catalysts. As the thickness of the sample (, 2 mm) was above the critical value, a temporary temperature increase ("exo effect") was observed during all quasi-isothermal decompositions studied, irrespective of the reaction temperature. Increasing the reaction temperature resulted in a shift of the exo effect towards shorter times and an increased content of maghemite phase. The maghemite content decreases above 350 °C as a result of a thermally induced polymorphous transition into hematite. The catalytic data demonstrate that the crystal structure of iron(III) oxide (i.e. the relative contents of maghemite and hematite) does not influence the rate of hydrogen peroxide decomposition. However, the rate constant increases monotonously with increasing sample surface area (and decreasing thermolysis temperature), reaching a maximum of 27,×,10,3 min,1(g/L),1 for the sample with a surface area of 285 m2,g,1. This rate constant is currently the highest reported value of all known iron oxide catalytic systems and is even slightly higher than that observed for the most efficient catalyst reported to date, which has a significantly larger surface area of 337 m2,g,1. This surprisingly high catalytic activity at relatively low surface area can be ascribed to the absence of a amorphous phase in the samples prepared in this study. Taking into account these new findings, the contributions of the key factors highlighted above (surface area, particle size, crystal structure, crystallinity) to the overall activity of iron oxides forhydrogen peroxide decomposition are discussed. [source]


Conformational Flexibility in a Carbobicyclic Diphosphinite Ligand

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 20 2007
Ian J. S. Fairlamb
Abstract An unsymmetrical bicyclo[3.2.0]heptanyl diphosphinite ligand, FLEXIphosO, shows flexible coordination modes to palladium centres. The X-ray crystal structure for [Pd02(P,P,)3] has been determined which reveals that the bicyclic backbone of the FLEXIphosO ligand exists in an exo -envelope conformation. The change in conformation stands in stark contrast to that observed in mononuclear neutral and cationic palladium(II) complexes containing the FLEXIphosO ligand, where an endo -envelope is observed in solution and in the solid-state. Theoretical studies provide an insight into the relative stability of palladium(0) complexes containing the FLEXIphosO ligand. Another large spanning angle ligand, SPANphos, does not form a similar palladium(0) dimer complex under identical reaction conditions, highlighting the unusual behaviour of the FLEXIphosO ligand.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]


Entrapment of a Hexamer of Nitrobenzene Molecules between the Layers of (4,4)-Coordination Networks Containing Intra-,-Sheet Hydrogen Bonds

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 3 2006
Madhushree Sarkar
Abstract Two exo -bidentate pyridyl ligands containing diamides as spacers were shown to form non-interpenetrated 2D-coordination networks of (4,4)-geometry upon treatment with Cu(NO3)2 and NaSCN. The crystal structures reveal that both structures contain intralayer ,-sheet hydrogen bonds. In one of these structures nitrobenzene occupies 60,% of the crystal volume included between the coordination networks. The nitrobenzene molecules form a layer which has the hexameric C,H···O hydrogen bonded aggregate as a basic building block. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]


endo and exo Coordination of Indanol: Synthesis, Isolation and Structural Characterisation of [H3Ru3(endo -Indanol)(C6Me6)2(O)]+ and [H3Ru3(exo -Indanol)(C6Me6)2(O)]+ as Their Tetrafluoroborate Salts

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 19 2004
Ludovic Vieille-Petit
Abstract The reaction of 2,3,4,7-tetrahydro-1H -inden-2-ol with ruthenium chloride hydrate in refluxing ethanol yields the chloro-bridged dinuclear complex [RuCl2(indanol)]2 (1). The mononuclear complex [Ru(indanol)(H2O)3]2+ (2), formed in situ from 1 in aqueous solution, reacts with the dinuclear complex [H3Ru2(C6Me6)2]+ to give a trinuclear arene-ruthenium cluster as a mixture of two isomers, the cations [H3Ru3(endo -indanol)(C6Me6)2(O)]+ (3a) and [H3Ru3(exo -indanol)(C6Me6)2(O)]+ (3b), in a 1:1 ratio. The hydroxy function of the indanol ligand is oriented towards the ,3 -oxo cap of 3a, whereas the OH group is bent away from the metal skeleton of 3b. These two isomers, which can easily be separated by silica-gel chromatography, were isolated and characterised as their tetrafluoroborate salts. The single-crystal X-ray structure analysis of [3a][BF4] shows a strong intramolecular hydrogen bond between the ,3 -oxo ligand and the hydroxyl function, which even persists in acetone solution, as demonstrated by NMR spectroscopy. On the other hand, the hydroxy function of 3b was found to be free in the solid state as well as in solution, as shown by an X-ray crystal structure analysis and by NMR spectroscopy. The catalytic activities of the water-soluble trinuclear cations 3a and 3b for the hydrogenation of benzene to give cyclohexane under biphasic conditions are considerably different, the exo isomer 3b being more active than the endo isomer 3a. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]


Lewis Acid Mediated Aminobenzannulation Reactions of ,-Ketoalkynes: Synthesis of 1-Aminocarbazoles and 9-Aminopyrido[1,2- a]indoles

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 17 2009
Diego Facoetti
Abstract 2-Acyl- N -propargylindoles 1 and 2-acyl-3-propargylindoles 5 undergo aminobenzannulation reactions with pyrrolidine in the presence of an appropriate Lewis acid to give 9-aminopyrido[1,2- a]indoles 6 and 1-aminocarbazoles 7, respectively. The selection of the appropriate Lewis acid, TiCl4 or GaCl3 for 1 and InCl3 for 5, allows the domino process involving the initial formation of an enamine intermediate, followed by a regioselective 6- exo - dig intramolecular nucleophilic attack of the nucleophilic terminus of the unsaturated system (the ,-carbon of the enamino moiety) to the carbon,carbon triple bond. Moreover, several features concerning the reaction mechanism and the role of both catalysts, in connection with the electronic properties of the reacting alkynes, are reported. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]


On the Mechanism of the Puzzling "Endocyclic" Skeletal Rearrangement of 1,6-Enynes

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 25 2007
Noemí Cabello
Abstract Skeletal rearrangements of simple 1,6-enynes have been studied in order to determine the factors that control the formation of five- or six-membered rings. Simple 1,6-enynes substituted only at C-4 preferentially give six-membered rings on skeletal rearrangement in the presence of gold(I) catalysts, whereas increasing electron-withdrawing character of substituents at C-4 leads to five-membered rings. Reactions of these simple enynes in the presence of PtCl4 as catalyst give exclusively exo - double skeletal rearrangements. Enynes substituted at the alkyne also react with AuI catalysts to give exclusively products of exo - double rearrangement. The different mechanisms have been analyzed by DFT calculations. Although a pathway for the formation of six-membered rings involving two steps in a ring-expansion/ring-contraction process was found, the activation energy of the first step is too high. Instead, this skeletal rearrangement appears to follow an exo - single skeletal rearrangement in which the initial cyclopropyl gold carbene opens to form a six-membered ring. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]


4- exo - dig Cyclocarbopalladation: A Straightforward Synthesis of Cyclobutanediols from Acyclic ,-Bromopropargylic Diols under Microwave Irradiation Conditions,

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 6 2006
Christophe Bour
Abstract Treatment of acyclic ,-bromopropargylic diols with tributylstannylated alkynes under palladium catalysis and microwave irradiation conditions gives high yields of the bis(alkylidene)cyclobutanediol derivatives and cyclobutenediols through an efficient 4- exo - dig cyclocarbopalladation. The cyclization is general with a wide variety of alkyne derivatives and gives access to new cyclobutane ring systems bearing one exocyclic double bond and one eneyne substituent as well as bicyclic dienes sharing a common double bond that may be of interest for further elaborations of complex molecules. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]


Indoloquinolines, Indolobenzoxazines and Quinazolophthalazines Prepared from Norbornane/eneamino Acids and Hydrazides,

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 19 2005
Géza Stájer
Abstract The reactions of di -endo - and di -exo -aminonorbornane/enecarboxylic acids 1,4 with ethyl 2-(2-oxocyclohexyl)acetate afforded methanoindoloquinolines 5, 6, 8, and 9, the oxo ester participating as a two-membered sp2 building block. In the cases of di -exo - and di -endo -aminonorbornenecarboxylic acids 2 and 4, methanoindolobenzoxazinediones 7 and 10 were also formed; compound 7 was also isolated from the mother liquor of 10. The reactions of ethyl 2-(2-oxocyclohexyl)acetate with aminonorbornane/enecarbohydrazides 11,14 result in the methanoquinazolophthalazines 15,18. The structures of the compounds were elucidated by NMR spectroscopy, and for 6, 7, 8, and 10 also by X-ray crystallography. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]


Synergistic Effect of Pybox Substituents and Lanthanide Cations in Reversing the Asymmetric Induction in the Catalysed Diels,Alder Reaction between 3-Acryloyl-1,3-oxazolidin-2-one and Cyclopentadiene

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 14 2004
Giovanni Desimoni
Abstract The enantioselectivity in the pybox/lanthanide(III) triflate catalysed Diels,Alder reaction between cyclopentadiene and 3-acryloyl-1,3-oxazolidin-2-one is profoundly influenced by the presence of a phenyl group in the 5,-position of the ligand, since it sometimes amplifies, and sometimes reverses the enantioselectivity induced by the 4,-substituent. The results can be summarised in three points. Of the catalysts derived from (4,R,5,R)-4-Me-5-Ph-pybox (6), the ScIII -based one is both strongly endo -selective and strongly enantioselective. Several catalysts derived from (4,R,5,R)- trans -diphenyl-pybox (9) give up to 50% yields of exo - 4 and, at least with PrIII and LaIII, induce excellent ee values in both endo and exo adducts. The (4,R,5,S)- cis -diphenyl-pybox (8) is a novel and valuable ligand, since opposite enantiomers can be obtained with good selectivity simply by changing the cation from ScIII to LaIII. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]


An Investigation on the Synthesis of New Molecular Architectures from the Cyclotrimerisation of exo - and endo -Benzotricyclo[4.2.1.02,5]nonene

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 1 2004
Arif Dastan
Abstract We have performed an investigation on the cyclotrimerisation of molecules having exo - and endo -benzotricyclo[4.2.1.02,5]nonene skeletons (3 and 4) with the aim of producing their respective cyclotrimers 2 that feature unusual geometries and electronic properties. Activation towards the cyclotrimerisation reaction was performed using the vic -bromostannyl vinyl derivatives and was accomplished under copper-mediated or palladium-catalysed reaction conditions. While the exo isomer 3 proved to be quite reactive and afforded variable amounts of the syn and anti cyclotrimers, the endo isomer 4 turned out to be quite resistant to cyclotrimerisation because of steric hindrance. Only dimers and acyclic trimers were obtained from reactions using this substrate. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]


A Radical Version of the Bromo- and the Iodocyclization of Bis(homoallylic) Alcohols , The Synthesis of Halogenated Tetrahydrofurans by Stereoselective Alkoxyl Radical Ring Closures

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 20 2003
Jens Hartung
Abstract A new synthesis of bromo- and iodomethyl-substituted tetrahydrofurans has been devised. The sequence starts with the conversion of aryl-functionalized bis(homoallylic) alcohols 1 into N -alkenoxythiazole-2(3H)-thiones 6 or pyridine-2(1H)-thiones 7. When photolyzed in the presence of appropriate trapping reagents, thiones 6 and 7 efficiently liberated substituted 4-penten-1-oxyl radicals 2, which underwent synthetically useful 5- exo -trig cyclizations. Cyclized radicals 3 were trapped with BrCCl3 or an adequate iodine atom donor (either n -C4F9I or diethyl 2-iodo-2-methyl malonate) to provide halocyclization products 4 or 5. This strategy has been applied for the synthesis of 3-, 4-, or 5-phenyl-substituted 2-(1-bromo-1-methylethyl)tetrahydrofurans 4a,c (75,90%, 36,96% de), which were not attainable as major products from polar, for example NBS-mediated, bromocyclizations. Aryl-substituted 2-iodomethyl tetrahydrofurans 5 (46,80%) were prepared in a similar way starting from N -alkenoxypyridine-2(1H)-thiones 7 and a suitable iodine atom donor. Diastereomerically pure iodides cis - 5 and trans - 5 served as starting materials for a stereochemical analysis of disubstituted tetrahydrofurans by NMR spectroscopy and X-ray diffraction analysis. The results of this investigation clarified that all new alkoxyl radical cyclizations followed in terms of regio- and diastereoselectivity the general guidelines which had been established for this type of ring-closure reaction. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]


Blocking Fluorine Substitution in Biotransformation of Nortricyclanyl N -Phenylcarbamates with Beauveria bassiana

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 11 2003
Günter Haufe
Abstract The biotransformation of tricyclo[2.2.1.02,6]hept-3-yl N -phenylcarbamate (8) by a standard procedure using Beauveria bassiana gave a 7:1 mixture of optically active exo,exo - and exo,endo -5-hydroxytricyclo[2.2.1.02,6]hept-3-yl N -phenylcarbamates 15 and 16 in 19% isolated yield. No ring opening of the three-membered ring was observed. Substitution with a fluorine atom at the 5- endo - or 5- exo -position prevented hydroxylation of any alicyclic position of the molecules, p -hydroxylation of the aromatic ring occurring to a small extent instead. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]


Reactions of Silicon Atoms with Conjugated ,-Systems: A Matrix-Spectroscopic Study

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 3 2003
Günther Maier
Abstract The reaction of silicon atoms with cyclopentadiene and butadiene in argon at 10 K has been studied. Addition to the conjugated ,-system of cyclopentadiene occurs in a [1,4]-fashion. Upon irradiation the ,-adduct 3 rearranges to the formal insertion product 2 which has an unusual structure. Remarkably, a photoequilibrium between the two exo,endo isomers 2 and 4 can be observed. In the case of butadiene the addition is less stereospecific. The planar [1,4]-adduct 11 is formed together with the [1,2]-adduct 14. Surprisingly, besides 11 a second, nonplanar [1,4]-adduct 10 can be detected. The isomers 11 and 14 are transformed into 10 upon irradiation. The final photoproduct is silole 9. The structural elucidation of the new species is based on isotopic labelling and a comparison of the experimental observations with the results from density functional calculations. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]


A Concise and Efficient Synthesis of seco -Duocarmycin SA

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 3 2003
Lutz F. Tietze
Abstract A short and efficient synthesis of seco -duocarmycin SA (3), a highly potent cytostatic agent and direct precursor of the natural product duocarmycin SA (1), has been achieved. Starting from commercially available 2-methoxy-4-nitroaniline (4) the synthetic protocol contains a Fischer indole synthesis to introduce the heterocyclic scaffold and a radical 5- exo - trig cyclization to furnish the (chloromethyl)indoline ring system as key reactions. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]


Chemical composition of the essential oils of Astrodaucus persicus (Boiss.) Drude root, stem/leaves and flowers/fruits

FLAVOUR AND FRAGRANCE JOURNAL, Issue 2 2006
Y. T. Bazargani
Abstract The essential oils of Astrodaucus persicus (Boiss.) Drude were obtained by hydrodistillation of root and aerial parts and examined by GC and GC,MS. The composition of oil samples was compared; 22, 20 and 14 compounds were identified in the essential oils of the root, stem/leaves and flowers/fruits, representing 94.4%, 99.7% and 99.9%, respectively, of the total oils. The major components were bornyl acetate (26.5%), , -sesquiphellandrene (25.9%) and exo -fenchyl acetate (25.1%) for the root oil, , -pinene (56.4%) and exo -fenchyl acetate (37.7%) for the stem/leaves oil and , -pinene (46.1%), , -pinene (26.1%) and , -thujene (14.4%) for the flowers/fruits oil. The highest amount of sesquiterpenes was found in the root oil (30.7%). Copyright © 2005 John Wiley & Sons, Ltd. [source]


6-(Diazomethyl)-1,3-bis(methoxymethyl)uracil, Synthesis and Transformation into Annulated Pyrimidinediones

HELVETICA CHIMICA ACTA, Issue 7 2008
Fuyi Zhang
Abstract 6-(Diazomethyl)-1,3-bis(methoxymethyl)uracil (5) was prepared from the known aldehyde 3 by hydrazone formation and oxidation. Thermolysis of 5 and deprotection gave the pyrazolo[4,3- d]pyrimidine-5,7-diones 7a and 7b. Rh2(OAc)4 catalyzed the transformation of 5 into to a 2,:,1 (Z)/(E) mixture of 1,2-diuracilylethenes 9 (67%). Heating (Z)- 9 in 12n HCl at 95° led to electrocyclisation, oxidation, and deprotection to afford 73% of the pyrimido[5,4- f]quinazolinetetraone 12. The Rh2(OAc)4 -catalyzed reaction of 5 with 3,4-dihydro-2H -pyran and 2,3-dihydrofuran gave endo/exo -mixtures of the 2-oxabicyclo[4.1.0]heptane 13 (78%) and the 2-oxabicyclo[3.1.0]hexane 15 (86%), Their treatment with AlCl3 or Me2AlCl promoted a vinylcyclopropane,cyclopentene rearrangement, leading to the pyrano- and furanocyclopenta[1,2- d]pyrimidinediones 14 (88%) and 16 (51%), respectively. Similarly, the addition product of 5 to 2-methoxypropene was transformed into the 5-methylcyclopenta-pyrimidinedione 18 (55%). The Rh2(OAc)4 -catalyzed reaction of 5 with thiophene gave the exo -configured 2-thiabicyclo[3.1.0]hexane 19 (69%). The analoguous reaction with furan led to 8-oxabicyclo[3.2.1]oct-2-ene 20 (73%), and the reaction with (E)-2-styrylfuran yielded a diastereoisomeric mixture of hepta-1,4,6-trien-3-ones 21 (75%) that was transformed into the (1E,4E,6E)-configured hepta-1,4,6-trien-3-one 21 (60%) at ambient temperature. [source]


Synthesis of (+)-13-Stemarene and (+)-18-Deoxystemarin: Expeditious Preparation of the Key 6- exo -Hydroxybicyclo[2.2.2]octan-2-one, Ethylene Dithioacetal

HELVETICA CHIMICA ACTA, Issue 4 2008
Francesca Leonelli
Abstract An expeditious preparation of the 6- exo -hydroxybicyclo[2.2.2]octan-2-one ethylene dithioacetal 2b, a key intermediate in the synthesis of (+)-13-stemarene (4) and (+)-18-deoxystemarin (5) is described. Compound 2b was obtained as the major product by equilibrating the endo rich mixture of 6-hydroxybicyclo[2.2.2]octan-2-one ethylene dithioacetals 2 with TsOH in benzene at reflux, easily available from the corresponding hydroxy ketones 9. The model experiments which preceeded the above transformation, not previously described in the literature, are also presented. [source]


Reactions of Polycyclic Ketones with Dimethoxycarbene; a Convenient Route for a ,One-Pot' Preparation of Some , -Hydroxycarboxylic Acid Esters

HELVETICA CHIMICA ACTA, Issue 7 2007
Jaros, aw Roma
Abstract Polycyclic ,cage' ketones, such as pentacyclo[5.4.0.02,6.03,10.05,9]undecan-8-one (10), pentacyclo[5.4.0.02,6.03,10.05,9]undecane-8,11-dione (11), and adamantan-2-one (16) were treated with the nucleophilic dimethoxycarbene (DMC; 1), which was generated thermally from 2,5-dihydro-2,2-dimethoxy-5,5-dimethyl-1,3,4-oxadiazole (4a) in boiling toluene. In this ,one-pot' procedure, the , -hydroxycarboxylic acid ester 12 or a corresponding derivative 15 or 17 was obtained (Schemes,4,7). Additionally, ,cage' thione 21 was treated with DMC under the same conditions yielding dimethoxythiirane 22 (Scheme,8). Subsequent hydrolysis or desulfurization (followed by hydrolysis on silica gel) of 22 gave , -mercaptocarboxylate 25 and the corresponding desulfurized ester 24, respectively. In all cases, the addition of DMC occurred stereoselectively, and the addition from the exo -face is postulated to explain the structures of the isolated products. [source]


Benzo[a]heptalenes from Heptaleno[1,2- c]furans.

HELVETICA CHIMICA ACTA, Issue 4 2007

Abstract It is shown in this ,Part 2' that heptaleno[1,2- c]furans 1 react thermally in a Diels,Alder -type [4+2] cycloaddition at the furan ring with vinylene carbonate (VC), phenylsulfonylallene (PSA), , -(acetyloxy)acrylonitrile (AAN), and (1Z)-1,2-bis(phenylsulfonyl)ethene (ZSE) to yield the corresponding 1,4-epoxybenzo[d]heptalenes (cf. Schemes,1, 5, 6, and 8). The thermal reaction of 1a and 1b with VC at 130° and 150°, respectively, leads mainly to the 2,3- endo -cyclocarbonates 2,3- endo - 2a and - 2b and in minor amounts to the 2,3- exo -cyclocarbonates 2,3- exo - 2a and - 2b. In some cases, the (P*)- and (M*)-configured epimers were isolated and characterized (Scheme,1). Base-catalyzed cleavage of 2,3- endo - 2 gave the corresponding 2,3-diols 3, which were further transformed via reductive cleavage of their dimesylates 4 into the benzo[a]heptalenes 5a and 5b, respectively (Scheme,2). In another reaction sequence, the 2,3-diols 3 were converted into their cyclic carbonothioates 6, which on treatment with (EtO)3P gave the deoxygenated 1,4-dihydro-1,4-epoxybenzo[d]heptalenes 7. These were rearranged by acid catalysis into the benzo[a]heptalen-4-ols 8a and 8b, respectively (Scheme,2). Cyclocarbonate 2,3- endo - 2b reacted with lithium diisopropylamide (LDA) at ,70° under regioselective ring opening to the 3-hydroxy-substituted benzo[d]heptalen-2-yl carbamate 2,3- endo - 9b (Scheme,3). The latter was O -methylated to 2,3- endo -(P*)- 10b. The further way, to get finally the benzo[a]heptalene 13b with MeO groups in 1,2,3-position, could not be realized due to the fact that we found no way to cleave the carbamate group of 2,3- endo -(P*)- 10b without touching its 1,4-epoxy bridge (Scheme,3). The reaction of 1a with PSA in toluene at 120° was successful, in a way that we found regioisomeric as well as epimeric cycloadducts (Scheme,5). Unfortunately, the attempts to rearrange the products under strong-base catalysis as it had been shown successfully with other furan,PSA adducts were unsuccessful (Scheme,4). The thermal cycloaddition reaction of 1a and 1b with AAN yielded again regioisomeric and epimeric adducts, which could easily be transformed into the corresponding 2- and 3-oxo products (Scheme,6). Only the latter ones could be rearranged with Ac2O/H2SO4 into the corresponding benzo[a]heptalene-3,4-diol diacetates 20a and 20b, respectively, or with trimethylsilyl trifluoromethanesulfonate (TfOSiMe3/Et3N), followed by treatment with NH4Cl/H2O, into the corresponding benzo[a]heptalen-3,4-diols 21a and 21b (Scheme,7). The thermal cycloaddition reaction of 1 with ZSE in toluene gave the cycloadducts 2,3- exo - 22a and - 22b as well as 2- exo,3- endo - 22c in high yields (Scheme,8). All three adducts eliminated, by treatment with base, benzenesulfinic acid and yielded the corresponding 3-(phenylsulfonyl)-1,4-epoxybenzo[d]heptalenes 25. The latter turned out to be excellent Michael acceptors for H2O2 in basic media (Scheme,9). The Michael adducts lost H2O on treatment with Ac2O in pyridine and gave the 3-(phenylsulfonyl)benzo[d]heptalen-2-ones 28a and 3- exo - 28b, respectively. Rearrangement of these compounds in the presence of Ac2O/AcONa lead to the formation of the corresponding 3-(phenylsulfonyl)benzo[a]heptalene-1,2-diol diacetates 30a and 30b, which on treatment with MeONa/MeI gave the corresponding MeO-substituted compounds 31a and 31b. The reductive elimination of the PhSO2 group led finally to the 1,2-dimethoxybenzo[a]heptalenes 32a and 32b. Deprotonation experiments of 32a with t -BuLi/N,N,N,,N,-tetramethylethane-1,2-diamine (tmeda) and quenching with D2O showed that the most acid CH bond is HC(3) (Scheme,9). Some of the new structures were established by X-ray crystal-diffraction analyses (cf. Figs.,1, 3, 4, and 5). Moreover, nine of the new benzo[a]heptalenes were resolved on an anal. Chiralcel OD-H column, and their CD spectra were measured (cf. Figs.,8 and 9). As a result, the 1,2-dimethoxybenzo[a]heptalenes 32a and 32b showed unexpectedly new Cotton -effect bands just below 300,nm, which were assigned to chiral exciton coupling between the heptalene and benzo part of the structurally highly twisted compounds. The PhSO2 -substituted benzo[a]heptalenes 30b and 31b showed, in addition, a further pair of Cotton -effect bands in the range of 275,245,nm, due to chiral exciton coupling of the benzo[a]heptalene chromophore and the phenylsulfonyl chromophore (cf. Fig.,10). [source]


Are Oxazolidinones Really Unproductive, Parasitic Species in Proline Catalysis?

HELVETICA CHIMICA ACTA, Issue 3 2007
Experiments Pointing to an Alternative View, Thoughts
Abstract The N,O-acetal and N,O-ketal derivatives (oxazolidinones) formed from proline, and aldehydes or ketones are well-known today, and they are detectable in reaction mixtures involving proline catalysis, where they have been considered ,parasitic dead ends'. We disclose results of experiments performed in the early 1970's, and we describe more recent findings about the isolation, characterization, and reactions of the oxazolidinone derived from proline and cyclohexanone. This oxazolidinone reacts (THF, room temperature) with the electrophiles , -nitrostyrene and chloral (=trichloroacetaldehyde), to give the Michael and aldol adduct, respectively, after aqueous workup (Scheme,5). The reactions occur even at ,75° when catalyzed with bases such as 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) or EtN(i-Pr)2 (DIPEA) (10%; Table,1). It is shown by NMR (Figs.,1 and 3) and IR analysis (Figs.,2 and 4) that the primarily detectable product (before hydrolysis) of the reaction with the nitro-olefin is again an oxazolidinone. When dissolved in hydroxylic solvents such as MeOH, ,hexafluoroisopropanol' ((CF3)2CHOH; HFIP), AcOH, CF3COOH, or in LiBr-saturated THF, the ring of the oxazolidinone from cyclohexanone and proline opens up to the corresponding iminium ion (Tables,2,4), and when treated with strong bases such as DBU (in (D8)THF) the enamino-carboxylate derived from proline and cyclohexanone is formed (Scheme,8). Thus, the two hitherto putative participants (iminium ion and enamine) of the catalytic cycle (Scheme,9) have been characterized for the first time. The commonly accepted mechanism of the stereoselective C,C- or C,X-bond-forming step (i.e., A,D) of this cycle is discussed and challenged by thoughts about an alternative model with a pivotal role of oxazolidinones in the regio- and diastereoselective formation of the intermediate enamino acid (by elimination) and in the subsequent reaction with an electrophile (by trans -addition with lactonization; Schemes,11,14). The stereochemical bias between endo - and exo -space of the bicyclo[3.3.0]octane-type oxazolidinone structure (Figs.,5 and 6) is considered to possibly be decisive for the stereochemical course of events. Finally, the remarkable consistency, with which the diastereotopic Re -face of the double bond of pyrrolidino-enamines (derived from proline) is attacked by electrophiles (Schemes,1 and 15), and the likewise consistent reversal to the Si -face with bulky (Aryl)2C-substituents on the pyrrolidine ring (Scheme,16) are discussed by invoking stereoelectronic assistance from the lone pair of pyramidalized enamine N-atoms. [source]


Synthesis of Monosaccharide-Derived Spirocyclic Cyclopropylamines and Their Evaluation as Glycosidase Inhibitors

HELVETICA CHIMICA ACTA, Issue 9 2003
Christian Blüchel
The glucose-, mannose-, and galactose-derived spirocyclic cyclopropylammonium chlorides 1a,1d, 2a,2d and 3a,3d were prepared as potential glycosidase inhibitors. Cyclopropanation of the diazirine 5 with ethyl acrylate led in 71% yield to a 4,:,5,:,1,:,20 mixture of the ethyl cyclopropanecarboxylates 7a,7d, while the Cu-catalysed cycloaddition of ethyl diazoacetate to the exo -glycal 6 afforded 7a,7d (6,:,2,:,5,:,3) in 93,98% yield (Scheme,1). Saponification, Curtius degradation, and subsequent addition of BnOH or t- BuOH led in 60,80% overall yield to the Z- or Boc-carbamates 11a,11d and 12a,12d, respectively. Hydrogenolysis of 11a,11d afforded 1a,1d, while 12a,12d was debenzylated to 13a,13d prior to acidic cleavage of the N -Boc group. The manno - and galacto -isomers 2a,2d and 3a,3d, respectively, were similarly obtained in comparable yields (Schemes,2 and 4). Also prepared were the differentially protected manno- configured esters 24a,24d; they are intermediates for the synthesis of analogous N -acetylglucosamine-derived cyclopropanes (Scheme,3). The cyclopropylammonium chlorides 1a,1d, 2a,2d and 3a,3d are very weak inhibitors of several glycosidases (Tables,1 and 2). Traces of Pd compounds, however, generated upon catalytic debenzylation, proved to be strong inhibitors. PdCl is, indeed, a reversible, micromolar inhibitor for the ,- glucosidases from C. saccharolyticum and sweet almonds (non-competitive), the , -galactosidases from bovine liver and from E. coli (both non-competitive), the , -galactosidase from Aspergillus niger (competitive), and an irreversible inhibitor of the , -glucosidase from yeast and the , -galactosidase from coffee beans. The cyclopropylamines derived from 1a,1d or 3a,3d significantly enhance the inhibition of the ,- glucosidase from C. saccharolyticum by PdCl, lowering the Ki value from 40,,M (PdCl) to 0.5,,M for a 1,:,1 mixture of PdCl and 1d. A similar effect is shown by cyclopropylamine, but not by several other amines. [source]


Multiple keratoacanthomas in a young woman: report of a case emphasizing medical management and a review of the spectrum of multiple keratoacanthomas

INTERNATIONAL JOURNAL OF DERMATOLOGY, Issue 1 2007
Ron J. Feldman MD
A 27-year-old white woman was referred for consultation with regard to the presence of extensive multiple keratotic lesions. She began to develop these lesions at the age of 9 years, with healing of the lesions resulting in scar formation. A biopsy was performed at the age of 16 years, but the patient was unsure of the results. Since then, she had not had any treatment or biopsies, and stated that she had not suffered from any health problems during the intervening period. She was most concerned about the tumors on her heels and soles, which caused difficulty with ambulation. The family history was negative for skin diseases, including melanoma, nonmelanoma skin cancer, psoriasis, and eczema, and positive for Type II diabetes mellitus. A relative reported that the patient's grandfather had similar lesions, but the patient's parents and siblings were healthy. She was married and had one child, a 9-year-old daughter. Her child had no skin lesions. The patient's only medication was Ortho-Tricyclene birth control pills. She had no known drug allergies. Physical examination revealed the presence of multiple lesions on her body (Fig. 1). Her left superior helix contained a well-demarcated, dome-shaped nodule with a rolled, mildly erythematous border with a central hyperkeratotic plug. A similar lesion was present in the scaphoid fossa of the left ear and smaller lesions were scattered on her face. Numerous lesions were present on the arms and legs bilaterally, with the majority of lesions being located on the anterior lower legs. There were also lesions present on the palms and soles. The lesions ranged in size from 5 mm to 3 cm, the largest being a verrucous exophytic nodule on the anterior aspect of her left leg. Overall, there appeared to be two distinct types of lesion. One type appeared round, oval, and symmetric with a central keratotic plug, similar to that on the ear. The other type was larger, more exophytic, and verrucous, including the lesions on the volar surfaces. Also present were numerous, irregularly shaped atrophic scars where previous lesions had healed spontaneously. There were no oral lesions or lesions on her fingernails or toenails, and her teeth and hair were normal. Figure 1. Initial presentation of left ear and anterior legs before treatment A biopsy was obtained from an early lesion on the right dorsal forearm. Histology revealed an exo-/endophytic growth having a central crater containing keratinous material (Fig. 2). The crater was surrounded by markedly hyperplastic squamous epithelium with large squamous epithelial cells having abundant glassy cytoplasm. Some cells were dyskeratotic. Within the dermis was a dense, chiefly mononuclear inflammatory infiltrate. A buttress of epidermis surrounded the crater. The clinical and pathologic data were consistent with keratoacanthomas. Figure 2. Keratoacanthoma exhibiting an exo- and endophytic growth pattern with a central crater containing keratin (hematoxylin and eosin; original magnification, ×40) Initial laboratory screenings revealed elevated triglycerides and total cholesterol, 537 mg/dL (normal, < 150 mg/dL) and 225 mg/dL (normal, < 200 mg/dL), respectively, with all other laboratory results within normal limits. In anticipation of starting oral retinoid therapy for her multiple keratoacanthomas, she was referred to her primary care physician for control of hyperlipidemia. After her lipids had been controlled, she was placed on isotretinoin (Accutane) 40 mg/day. There was some interval improvement with regression of some lesions leaving atrophic scars. She was also started on topical application of tazarotene (Tazorac) for all nonresolving lesions. Possible side-effects from the isotretinoin occurred, including dry mouth and eyes. After 8 months of isotretinoin, the patient was switched to acitretin (Soriatane) 25 mg to determine whether it might have a more beneficial effect on the resistant lesions. Many of the larger lesions regressed leaving atrophic scars. The dose of acitretin was subsequently increased to 35 mg because the lesions on her heel and the ball of her foot persisted. Almost all of the lesions resolved, except those on her feet, which are slowly regressing. Currently, the patient is on a regimen of acitretin 25 mg once a day with tazarotene 0.1% gel applied directly to the few residual keratoacanthomas on her feet, which are slowly improving. [source]


Catalytic Dicyanative 5- exo- and 6- endo -Cyclization Triggered by Cyanopalladation of Alkynes

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 5 2010
Shigeru Arai
Abstract A stereoselective dicyanative 5- exo- and 6- endo -cyclization using various enynes has been investigated. The mode of cyclization is critically controlled by the structure of the substrates. For example, N -allyl derivatives prefer 5- exo -cyclization, while methacryloyl amides are transformed to the corresponding lactams with tetra -substituted carbons at the alpha-position via 6- endo -cyclization. Both reactions include syn -cyanopalladation to carboncarbon triple bonds in the initial step, and sequential cyclization followed by reductive elimination in one operation enables the construction of the highly functionalized nitrogen heterocycles. The scope of suitable substrates and a proposed mechanism are also described. [source]


Immobilization of MacMillan Imidazolidinone as Mac-SILC and its Catalytic Performance on Sustainable Enantioselective Diels,Alder Cycloaddition

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 5 2010
Hisahiro Hagiwara
Abstract MacMillan's imidazolidinone catalyst was immobilized as a supported ionic liquid catalyst (Mac-SILC) in the pores of silica gel with the aid of an ionic liquid , 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. The heterogenized organocatalyst was utilized for the enantioselective Diels,Alder reaction of cyclopentadiene and cinnamaldehyde, recovered by simple filtration and subsequent evacuation, and repeatedly used up to six times in 81% average chemical yield, 87% ee for endo - and 80% ee for exo -products. The Mac-SILC was effective for a variety of substrates. [source]