03 Fakultät Chemie

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    On attempts at solvolytic generation of aryl cations
    (1976) Subramanian, Lakshminarayanapuram R.; Hanack, Michael; Chang, Lawrence W. K.; Imhoff, Michael A.; Schleyer, Paul v. R.; Effenberger, Franz; Kurtz, Walter; Stang, Peter; Dueber, Thomas E.
    The solvolysis of phenyl triflate (3), phenyl nonaflate (4), o-methylphenyl nonaflate (5), o-cyclopropylphenyl nonaflate (6), o-methoxyphenyl triflate (7), 2,6-dimethoxyphenyl triflate (S), 2,6-diisopropylphenyl triflate (9), 33- dimethoxyphenyl triflate (lo), 3,5-dicyclopropylphenyl triflate (11), 3,5-di(2-methylcyclopropyl)phenyl triflate (12), 2,4,6-tricyclopropylphenyltr iflate (13), and 2,4,6-triisopropylphenytlr iflate (14) were examined in great detail under a wide variety of conditions. In highly polar nonnucleophilic solvents no reaction was observed and the unreacted triflates were recovered quantitatively. In the presence of nucleophiles or nucleophilic solvents the sole products observed were the corresponding phenols. Careful labeling and product studies showed that these phenols arose by nucleophilic attack on sulfur and S-0 bond cleavage. We have not been able to find any evidence for aryl cation intermediates.
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    Properties of amphiphilic terminally substituted conjugated nonaene- and 2-docosylnonaene carboxylic acids in monolayers at the air-water interface
    (1991) Effenberger, Franz; Meller, Paul; Ringsdorf, Helmut; Schlosser, Hubert
    In the present communication, we report thesynthesis of conjugated nonaene- and 2-docosylnonaene carboxylic acids with different terminal substituents. These substituents have been chosen so that their spectroscopic properties differ from those of the polyene chain; they also have specific electron donor, electron acceptor or redox properties to allow for specific and selective excitation (energy intake). Because of the amphiphilic character of these compounds, pressure-area isotherms were determined in monolayers at the air-water interface.
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    A novel synthetic route to L-proline (Amino acids ; 7)
    (1986) Drauz, Karl-Heinz; Kleemann, Axel; Martens, Jürgen; Scherberich, Paul; Effenberger, Franz
    Reaction of L-5-oxoproline esters L-2 with phosgene at 0° C gives L-5,51-dichloro-1-(chlorocarbonyl)proliene esters L-6 ,which readily lose hydrogen chloride to form L-5-chloro-1-(chloroarbonyl)-4,5-dehydroproline esters L-7. Catalytic hydrogenation (Pd/C, 180 bar) of L-7 yields L-1-(chlorocarbonyl)proline esters L-15 and thence, upon hydrolysis, L-proline ( L17 ). A "one-pot reaction" for the whole sequence is described, starting from easily accessible L-5-oxoproline esters and yielding L-proline in 78% overall yield and 99.7% optical purity.
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    Experimental and theoretical aspects of the formation of radical cations from tripyrrolidinobenzenes and their follow-up reactions
    (1990) Effenberger, Franz; Stohrer, Wolf-Dieter; Mack, Karl Ernst; Reisinger, Friedrich; Seufert, Walter; Kramer, Horst E.A.; Föll, Rudolf; Vogelmann, Ekehardt
    Tripyrrolidinobenzene radical cations(1*+), obtained from the corresponding arenes by oxidation with silver nitrate, are specially stabilized and thus allow specific reaction pathways of arene radical cations to be investigated separately and individually. Radical cations 1*+ ,for instance, generated under exclusion of oxygen, undergo dimerization to 2, or they abstract hydrogen from the solvent to form 3. In a pure oxygen atmosphere, the O2 reaction products 6 and 7 are formed, respectively, either exclusively or together with 2 and 3. Kinetic measurements give the following order of reactivity for these individual processes: reaction with O2 > dimerization. > H-abstraction from solvent. The changes in the product spectrum upon modification of the reaction conditions are in accord with the kinetic results. The dimeric u complexes 2 show surprisingly facile dissociation into two radical cations, two (1*+)with a much higher dissociation rate for the alkyl derivatives 2b-d than for 2a. Dissociation is enhanced substantially by light or in the presence of π donors. Individual product formation, rate of reactions of the radical cations 1*+, and photochemical cleavage of the dimeric σ complexes 2 can be rationalized, by qualitative and quantitative MO considerations, in terms of their relative frontier orbital energies.
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    Targeted methylation of the epithelial cell adhesion molecule (EpCAM) promoter to silence its expression in ovarian cancer cells
    (2014) Nunna, Suneetha; Reinhardt, Richard; Ragozin, Sergey; Jeltsch, Albert
    The Epithelial Cell Adhesion Molecule (EpCAM) is overexpressed in many cancers including ovarian cancer and EpCAM overexpression correlates with decreased survival of patients. It was the aim of this study to achieve a targeted methylation of the EpCAM promoter and silence EpCAM gene expression using an engineered zinc finger protein that specifically binds the EpCAM promoter fused to the catalytic domain of the Dnmt3a DNA methyltransferase. We show that transient transfection of this construct increased the methylation of the EpCAM promoter in SKOV3 cells from 4–8% in untreated cells to 30%. Up to 48% methylation was observed in stable cell lines which express the chimeric methyltransferase. Control experiments confirmed that the methylation was dependent on the fusion of the Zinc finger and the methyltransferase domains and specific for the target region. The stable cell lines with methylated EpCAM promoter showed a 60–80% reduction of EpCAM expression as determined at mRNA and protein level and exhibited a significantly reduced cell proliferation. Our data indicate that targeted methylation of the EpCAM promoter could be an approach in the therapy of EpCAM overexpressing cancers.
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    Über die Reaktion von 2,2-Dimethylpropylidinphosphan mit Wolframhexachlorid : die Kristallstrukturen von [(Cl3PO)WCl4(H9C4-C≡C-C4H9)] und [(H5C6)4As][WCl6]
    (1983) Uhl, Gudrun; Hey, Evamarie; Becker, Gerd; Weller, Frank; Dehnicke, Kurt
    Die Reaktion von 2,2-Dimethylpropylidinphosphan, (CH3)3C-C ≡P|, mit Wolframhexachlorid als Suspension in POCl 3 führt unter Oxydation des Phosphors zu 2,2,5,5-Tetramethylhex-3-in, das mit zugleich entstandenem Wolframtetrachlorid den durch POCl 3 solvatisierten, dunkelgrünen Alkinkomplex [(Cl3PO)WCl4(HgC4-C≡C-C4Hg)] bildet. Ein Teil des Wolframhexachlorids wird nur zu Wolframpentachlorid reduziert und kann nach Zugabe von Tetraphenylarsoniumchlorid als [(H5C6)4As][WCl6] isoliert werden. Für diese Verbindung wird eine neue, sehr einfache Synthese aus WCl6, [(H5C6)4As]Cl und C2Cl4 als Reduktionsmittel beschrieben.Die Struktur von [(Cl3PO)WCl4(H9C4-C≡C-C4H9)] wurde mit Hilfe von Röntgenbeugungsdaten ermittelt (R = 5,8%). Der Komplex kristallisiert monoklin in der Raumgruppe P21/n mit: {a = 1510; b = 1517; c = 849 pm; β 93,1°, Z = 4}. Das Wolframatom ist durch vier äquatorial angeordnete Chloratome, durch die C°C-Gruppe des Acetylen-Liganden und in trans-Position hierzu durch das Sauerstoffatom des POCl3-Moleküls siebenfach koordiniert. Der fast symmetrisch gebundene, voluminöse Acetylenligand drückt die Chloratome in Richtung auf das solvatisierte POCl3-Molekül weg, so daß keine gemeinsame Ebene mit dem Wolframatom möglich ist. Die C°C-Bindungslänge des 2,2,5,5-Tetramethylhex-3-in-Liganden entspricht mit 130 pm dem für eine C°C-Doppelbindung typischen Wert.Das IR-Spektrum von [(H5C6)4As][WCl6] läßt zwei WCl6-Valenzschwingungen erkennen und beweist damit die Verzerrung des regulären Oktaeders. Nach der Kristallstrukturbestimmung (Raumgruppe P4/n; a = 1301; c = 780 pm; Z = 2; R = 2,7%) besitzt das [WCl6]−-Ion annähernd C4V-Symmetrie mit etwas kürzeren W-Cl-Bindungslängen entlang der vierzähligen Drehachse.
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    Molekül- und Kristallstruktur des Methyl[(N-phenyl,N-trimethylsilyl)thiocarbamoyl]trimethylsilylphosphans (Acyl- und Alkylidenphosphane ; 27)
    (1985) Becker, Gerd; Massa, Werner; Schmidt, Roland E.; Uhl, Gudrun
    Das durch Addition von Methylbis(trimethylsilyl)phosphan an Phenylisothiocyanat gebildete [1] Methyl[(N-phenyl,N-trimethylsilyl)thiocarbamoyl]trimethylsilylphosphan 1a kristallisiert monoklin in der zentrosymmetrischen Raumgruppe P21/n mit folgenden, bei einer Meßtemperatur von -80 ± 3°C bestimmten Abmessungen der Elementarzelle: a=1041,2(4); b=1706,9(12); c=1001,1(6) pm; β-106,41(4)°; Z = 4. Die Röntgenstrukturanalyse (Rw = 0,039) bestätigt die bereits aus den NMR-Spektren abgeleitete Konstitution der Verbindung mit an Phosphor- und sp2-hybridisiertes Stickstoffatom gebundenen Trimethylsilyl-Gruppen. Charakteristische gerundete Bindungslängen und -winkel sind: P-Si 231, P-CH3 184, P-C(S) 187, C=S 167, N-C(S) 137 und N-Si 181pm sowie P-C-S 122°, P-C-N 117° und S-C-N 121°.
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    Durch Überexpression in der Hefe Pichia pastoris zu erhöhter Enantioselektivität : ein neues Kapitel in der Anwendung von Schweineleberesterase
    (2001) Musidlowska, Anna; Lange, Stefan; Bornscheuer, Uwe Theo
    Lipases and Esterases can be used as efficient biocatalysts for the preparation of a wide variety of optically pure compounds. Whereas a range of lipases - especially of microbial origin - are commercially available, only a few esterases can be obtained for the kinetic resolution of racemates or desymmetrization. In the majority of publications, pig liver esterase (PLE) is used, which is isolated from pig liver by extraction. Although it could be demonstrated, that this preparation can convert a broad range of compounds at partially very high stereoselectivity, its application is encountered with a number of disadvantages.
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    Elektronen-Transfer bei den Reaktionen von Halogen-σ-Komplexen des 1,3,5-Tris(1-pyrro-lidinyl)benzols mit Nucleophilen (Aminobenzole ; 21)
    (1990) Effenberger, Franz; Bäuerle, Peter; Seufert, Walter; Stohrer, Wolf-Dieter
    Iodo, bromo, chloro, and thiocyanato σ-complexes 4, accessible as crystalline compounds from 1,3,5-tris(1-pyrrolidinyl)benzene (1) with halogens and dirhodan, respectively, react with nucleophiles or bases under dehalogenation, deprotonation, dimerization, or H σ-complex formation. The product formation depends on the redox potentials of the σ-complexes (acceptors) and the nucleophiles (donors), on the leaving tendency of the substituents on C-1 of the σ-complexes, and on the reaction time. The unexpected reactions are interpreted by an electron transfer from the nucleophile Y| to the σ-complex A+ to give the radical A*, a subsequent heterolytic dissociation to the 1,3,5-tris(1-pyrrolidinyl)benzene radical cation C.+, and its follow-up reactions (addition of nucleophiles, dimerization, and H abstraction). The H σ-complex 6 results the most stable final product after long reaction times because of its lowest acceptor properties and the poor nucleofugal leaving tendency of a hydride ion.
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    Photoregulation of α-chymotrypsin activity in organic media : effects of bioimprinting
    (1994) Willner, Itamar; Lion-Dagan, Mazzi; Rubin, Shai; Wonner, Johann; Effenberger, Franz; Bäuerle, Peter
    α-Chymotrypsin exhibits photoswitchable activities in an organic solvent after covalent modification of the protein backbone with thiophenefulgide active ester (2). The thiophenefulgide-modified α-chymotrypsin exhibits reversible photoisomerizable properties between states (3)-E and (3)-C. The modified α-chymotrypsin, where nine lysine residues are substituted by thiophenefulgide units, retains 60% of the activity of the native enzyme. The activities of thiophenefulgide-modified α-chymotrypsin toward esterification of N-acetyl-L-phenylalanine (4) by ethanol in cyclohexane are controlled by the configuration of the attached photoisomerizable component and by prior bioimprinting of the protein backbone with the reaction substrate (4). The esterification of (4) in cyclohexane using bioimprinted (3)-C is two-fold faster than in the presence of (3)-E. In the presence of a nonbioimprinted enzyme, esterification of (4) by (3)-C is five-fold faster than with (3)-E. The activity of bioimprinted (3)-E toward esterification of (4) is 4.5-fold higher than that of nonbioimprinted (3)-E. Switchable cyclic esterification of (4) is accomplished by sequential photoisomerization of the thiophenefulgide-modified α-chymotrypsin between states (3)-C and (3)-E.