Synthese und Konfigurationszuordnung von potentiell antimikrobiellen 5,6-Dihydroxyisobenzofuranonen

Summary Oxidation of isobenzofuranone1 yielded in a diastereoselective reaction epoxide2. Acidolysis of2 resulted in a mixture oftrans-glycols6 a (88%) and7 a (4%), which were separated by crystallization. The relative configuration of6 a and7 a at the chiral centers 3 a, 5, 6, and 7 a was determined by¹H-NMR-spectroscopy and X-ray analysis of O-acetylated and 7 a-methylated derivatives.

     

Chemoselective Removal of Protecting Groups from O-Glycosyl Amino Acid and Peptide (Methoxyethoxy)ethyl Esters Using Lipases and Papain

The selective C-terminal deprotection of O-glycopeptide (methoxyethoxy)ethyl esters is achieved under mild conditions (pH 6.6, 37 degrees C) by enzymatic hydrolysis using papain or lipase M from Mucor javanicus to give building blocks useful for chain-extending glycopeptide synthesis. On the other hand, the selective removal of acetyl protecting groups from the saccharide portion of glycopeptides is accomplished by alternative enzymatic hydrolysis with lipase WG from wheat germ to furnish model substrates for enzymatic glycosyl transfer reactions in order to extend the carbohydrate side chain of these conjugates.     

R?ntgenspektrometrische Goldbestimmung in sulfidischen Erzen nach chemischer Anreicherung

Zusammenfassung Es wird eine Goldbestimmung an sulfidischen Erzen für den Bereich von 0,05–5 ppm bei 20 g Einwaage beschrieben. Das Gold wird durch Salpetersäurebehandlung von den übrigen Metallen getrennt, mit Salzsäure/ Salpetersäure gelöst und mit Selen als innerem Standard und Tellur als Spurenfänger mittels Zinn(II)-chlorid gefällt. Der Niederschlag wird auf ein Membranfilter aufgezogen. Die Goldbestimmung erfolgt über den Impulsratenquotienten der Gold L- und Selen K-Linien. Die störende Molybdän K-Strahlung und die Comptonstreuung werden durch ein Zirkoniumblech auf dem Röhrenfenster unterdrückt. Der Variationskoeffizient beträgt 20% für 0,2–5 ppm und 53,6% für 0,05 ppm.

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Summary A method is described for the determination of gold in sulphide ores within the concentration range of 0.05–5 ppm with sample weights of 20 g. Gold is separated from the other metals by treatment with nitric acid, dissolved by hydrochloric acid, containing some nitric acid, and is finally precipitated by stannous chloride applying selenium as internal standard and tellurium as collecting agent. The precipitate is mounted on a diaphragm filter and the determination of gold is carried out by X-ray analysis suppressing the disturbing Mo _K radiation and compton scattering by a zirconium sheet-metal on the X-ray tube. The pulse rate quotient of the lines Au _L /Se _K is a function of the concentration of gold. The variation coefficient is 20% for 0.2–5 ppm and 53.6% for 0.05 ppm.

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Herrn Prof. Dr.-Ing. habil. J. Hesemann zum 65. Geburtstag gewidmet.     

Perfluororganocadmium-verbindungen als sehr wirksame perfluoralkylierungs- und perfluorphenylierungsmittel zur darstellung von perfluororganozinn- und -blei-verbindungen [1]

Perfluoroorgano tin and lead compounds can be prepared in high yields from the reactions of (CH₃)₃SnOCOCF₃ and (CH₃)₃Pb(OCOCF₃) with perfluoroorgano cadmium complexes. (CH₃)₃SiOCOCF₃ reacts with (CF₃)₂Cd complexes — probably via the intermediate (CH₃)₃SiCF₃ and CF₂ elimination — to form (CH₃)₃SiF and CF₃CdOCOCF₃ complexes. While the reaction of (CF₃)₂Cd·D with (CH₃)₃SnONO₂ yields CF₃NO as the only volatile product, (R_f)₂Cd·D (R_f  C₂F₅, iC₃F₇) forms R_fCdONO₂·D and (CH₃)₃SnR_f. The preparations and properties of the partly new compounds as well as the n.m.r. spectra are described.     

Equational partiality

A special kind of partiality of heterogeneous algebraic structures is introduced. Every operator of a heterogeneous operator domain is associated with a set of term equations as necessary and sufficient domain condition.It is shown that some kind of hierarchy condition for the system of domain equations is equivalent to the condition that every injective weak homomorphism is a strong homomorphism which is equivalent to the statement that every bijective weak homomorphism is an isomorphism.On the base of this result the notions of a quasi-variety and of a variety of equationally partial heterogeneous algebras are suggested. The class of all small categories becomes a standard example of a variety of equational partial heterogeneous algebras.Presented by V. Trnková.     

Comprehensive two-dimensional liquid chromatography for the characterization of functional acrylate polymers

Comprehensive two-dimensional liquid chromatography-size-exclusion chromatography (LC x SEC) was investigated as a tool for the characterization of functional poly(methyl methacrylate) (PMMA) polymers. Ultraviolet-absorbance and evaporative light-scattering detection (ELSD) were used. A simple method to quantify ELSD data is presented. Each data point from the ELSD chromatogram can be converted into a mass concentration using experimental calibration curves. The qualitative and quantitative information obtained on two representative samples is used to demonstrate the applicability of LC x SEC for determining the mutually dependent molar-mass distributions (MMD) and functionality-type distributions (FTD) of functional polymers. The influence of the molar mass on the retention behavior in LC was investigated using LC x SEC for hydroxyl-functional PMMA polymers. The critical conditions, at which retention is--by definition--independent of molar mass, were not exactly the same for PMMA series with different end-groups. Our observations are in close agreement with theoretical curves reported in the literature. However, for practical applications of LC x SEC it is not strictly necessary to work at the exact critical solvent composition. Near-critical conditions are often sufficient to determine the mutually dependent distributions (MMD and FTD) of functional polymers.     

Duplex Stabilization of DNA: Oligonucleotides containing 7-substituted 7-deazaadenines

The oligonucleotide building blocks 4b–d derived from 7-bromo-, 7-chloro-, and 7-methyl-substituted 7-deaza-2′-deoxyadenosines 3b–d were prepared. They were employed in the solid-phase synthesis of the oligonucleotides 7–25 . The dA residues of the homomer d(A₁₂), the alternating d[(A-T)₆], and the palindromic d(G-T-A-G-A-A-T-T-C-T-A-C) were replaced by 3b–d as well as by the parent 7-deaza-2′-deoxyadenosine ( 3a ). The melting profiles and CD spectra of oligonucleotide duplexes, showing this major groove modification, were measured, and the T_m values as well as the thermodynamic data were determined. It was found that small substituents such as Br, Cl, or Me introduced in the 7-position of a 7-deazaadenine residue increase the duplex stability compared to oligonucleotides containing adenine.     

Specific labeling of cell surface proteins with chemically diverse compounds

The specific and covalent labeling of fusion proteins with synthetic molecules opens up new ways to study protein function in the living cell. Here we present a novel method that allows for the specific and exclusive extracellular labeling of proteins on the surfaces of live cells with a large variety of synthetic molecules including fluorophores, protein ligands, or quantum dots. The approach is based on the specific labeling of fusion proteins of acyl carrier protein with synthetic molecules through post-translational modification catalyzed by phosphopantetheine transferase. The specificity and versatility of the labeling should allow it to become an important tool for studying and manipulating cell surface proteins and for complementing existing approaches in cell surface engineering.