03 Fakultät Chemie
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Item Open Access A novel synthetic route to L-proline (Amino acids ; 7)(1986) Drauz, Karl-Heinz; Kleemann, Axel; Martens, Jürgen; Scherberich, Paul; Effenberger, FranzReaction 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.Item Open Access 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.Item Open Access Photoregulation of α-chymotrypsin activity in organic media : effects of bioimprinting(1994) Willner, Itamar; Lion-Dagan, Mazzi; Rubin, Shai; Wonner, Johann; Effenberger, Franz; Bäuerle, Peterα-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.Item Open Access 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, EkehardtTripyrrolidinobenzene 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.Item Open Access 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-DieterIodo, 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.Item Open Access 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, HubertIn 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.Item Open Access Microbial P450 enzymes in biotechnology(2004) Urlacher, Vlada B.; Lutz-Wahl, Sabine; Schmid, Rolf D.Oxidations are key reactions in chemical syntheses. Biooxidations using fermentation processes have already conquered some niches in industrial oxidation processes, since they allow the introduction of oxygen even into non-activated carbon atoms in a sterically and optically selective manner which is difficult or impossible to achieve by synthetic organic chemistry. Biooxidation using isolated enzymes is limited to oxidases and dehydrogenases. Surprisingly, cytochrome P450 monooxygenases (CYPs) have scarcely been studied for use in biooxidations, although they are one of the largest known superfamilies of enzyme proteins. Their gene sequences have been identified in various organisms such as humans, bacteria, algae, fungi and plants. The reactions catalyzed by P450s are quite diverse and range from biosynthetic pathways (e.g. those of animal hormones and secondary plant metabolites) to the activation or biodegradation of hydrophobic xenobiotic compounds (e. g. those of various drugs in the liver of higher animals). From a practical point of view, the great potential of P450s is limited by their functional complexity, low activity, and limited stability. In addition, P450-catalyzed reactions require a constant supply of NAD(P)H which makes continuous cell-free processes very expensive. Quite recently, several groups have started to investigate cost-efficient ways which could allow the continuous supply of electrons to the heme iron. These include, for example, the use of electron mediators, direct electron supply from electrodes and enzymatic approaches. In addition, methods of protein design and directed evolution have been applied in an attempt to enhance the activity of the enzymes and improve their selectivity. The promising application of bacterial P450s as catalyzing agents in biocatalytic reactions and recent progress made in this field are covered in this review.Item Open Access Photoswitchable binding of substrates to proteins : photoregulated binding of α-D-mannopyranose to concanavalin A modified by a thiophenefulgide dye(1992) Willner, Itamar; Rubin, Shai; Wonner, Johann; Effenberger, Franz; Bäuerle, PeterMacromolecules exhibiting photoswitchable physical or chemical properties are extensively examined as information storage and signal amplification materials. Photoregulated "on-of" biomaterials provide a novel means to design targeted therapeutic agents activated and deactivated by external light signals. Various means to photoregulate biotransformations by light-switchable enzymes have been described and include the modification of the enzyme active site and protein backbone by photochromic components and immobilization of enzymes in photochromic copolymers. Here we wish to report on the photoregulation of the binding properties of a protein by its chemical modification with photochromic units. We describe the photoswitchable binding of saccharides to concanavalin A modified by thiophenefulgide dye.Item Open Access Molekül- und Kristallstruktur des orthorhombischen (Diphenylmethyliden)mesitylphosphans (Acyl- und Alkylidenphosphane ; 29)(1986) Mundt, Otto; Becker, Gerd; Uhl, Werner; Massa, Werner; Birkhahn, MatthiasEine Röntgenstrukturanalyse an dem erstmals von Bickelhaupt u. Mitarb. [2] sowie später von uns auf anderem Wege [3] synthetisierten (Diphenylmethyliden)mesitylphosphan 1b {-125 ± 3°C; orthorhombisch; Pbca; a = 951,2(7); b = 2115,8(9); c = 1737,0(18)pm; Z = 8; Rg = 0,041} ergab folgende charakteristische Bindungslängen und -winkel: P=C 169,3(2); P-C 183, 0(2) pm; C-P=C 107,6(2)°; P=C-C 124,8(2)° bzw. 118,0(2)°. Diese Parameter stimmen zwar weitestgehend mit den von anderen Autoren [4] an einem monoklinen Polymorphen 1b bestimmten Werten überein; hinsichtlich seiner Molekülkonformation gleicht 1b aber eher Dem homologen (Diphenylmethyliden)mesitylamin 1a [5]. Während die Kristallstrukturen Von 1a und 1b als polytypoide Stapelvarianten mit gleich gepackten Molekülschichten eng miteinander Verwandt sind, ist eine entsprechende Beziehung zwischen 1b und 1b nicht zu erkennen.Item Open Access Poljarnost' i poljarizujemost' 3,3-dimetil-1-fosfabutina(1986) Išmajeva, Eleonora A.;; Pacanovskij, Igor I.; Stepanova, Ju. S.; Becker, Gerd; Knebl, Robert; Weeber, Ute; Pudovik, Arkadij N.-