Strukturelle Abwandlungen an N-Acetylneuraminsäuren, 8 Synthese von 7-, 8-, 9-Desoxy- und 4,7-Didesoxyneuraminsäure

The 7- and 8-Iodnonulosonic acid derivatives1 and2 react with tributyltinhydride-AIBN to the 7- and 8-deoxy-N-acetylneuraminic acid derivatives3 a and4 a which after hydrolysis give the 7-deoxy-N-acetylneuraminic acid3 b (5-N-acetamido-3,5,7-trideoxy--D-galacto-2-nonulopyranosidonic acid=7-Deoxy-Neu5Ac) and 8-deoxy-N-acetylneuraminic acid4 b (5-N-acetamido-3,5,8-trideoxy--D-galacto-2-nonulopyranosidonic acid=8-Deoxy-Neu5Ac). The 4,8,9-tris-(t-butyldimethylsilyl)-N-acetylneuraminic acid derivative5 a yields after transformation to the 7-O-acetyl compound5 b and partial removing of the protecting groups the derivative5 c. Further reaction with theMitsunobu-reagent and methyliodide affords the 9-Iodocompound6 a which turned to the 8-O-acetylderivative6 b. Subsequent reduction by means of tributyltinhydride yields first the 9-deoxyderivative7 a and after hydrolysis the 9-deoxy-N-acetylneuraminic acid7 b (5-N-acetyl amido-3,5,9-trideoxy-D-glycero--d-galacto-2-nonulopy-ranosidonic acid=9-Deoxy-Neu5Ac). Another synthesis of7 b follows the route8 f 8 g 7 c. The Deoxy-N-acetylneuraminic acid3 b could be prepared also by an alternative procedure using the methyl--8,9-methylethylen-4-O-t-butyldimethylsilyl-N-acetylneuraminic acid methylester8 a via the intermediate compounds8 d and8 e. Application of the 8,9-O-methylethyliden-N-acetylneuraminic acid derivative8 opens an approach to the xanthogenates8 a and8 b which could be reduced to the deoxy-N-acetylneuraminic acid derivatives9 a and10 a. Hydrolysis of10 a yields the 4,7-dideoxy-N-acetylneuraminic acid10 b (5-N-acetamido-3,4,5,7-tetradeoxy--D-lyxo-2-nonulopyranosidonic acid=4,7-Dideoxy-Neu5Ac).

     

Opening or Closing the Lock? When Reactivity Is the Key to Biological Activity

Thiol‐mediated processes play a key role to induce or inhibit inflammation proteins. Tailoring the reactivity of electrophiles can enhance the selectivity to address only certain surface cysteines. Fourteen 2′,3,4,4′‐tetramethoxychalcones with different α‐X substituents (X=H, F, Cl, Br, I, CN, Me, p‐NO₂‐C₆H₄, Ph, p‐OMe‐C₆H₄, NO₂, CF₃, COOEt, COOH) were synthesized, containing the potentially electrophilic α,β‐unsaturated carbonyl unit. The assessment of their reactivity as electrophiles in thia‐Michael additions with cysteamine shows a change in the reactivity of more than six orders of magnitude. Moreover, a clear correlation between their reactivity and an influence on the inflammation proteins heme oxygenase‐1 (HO‐1) and the inducible NO synthase (iNOS) is demonstrated. As the biologically most active compound, the α‐CF₃‐chalcone is shown to inhibit the NO production in RAW264.7 mouse macrophages in the nanomolar range.     

On a class of inequality problems with lack of compactness

In this paper we prove the existence of at least one solution for a variational-hemivariational inequality on a closed and convex set without using critical point theory. We apply a version of the well-known theorem of Knaster-Kuratowski-Mazurkiewicz. The obtained results can be applied to Schrödinger type problems and to problems with radially symmetric functions.     

Nucleophilic substitutions and radical reactions of phenylazocarboxylates

tert-Butyl phenylazocarboxylates are versatile building blocks for synthetic organic chemistry. Nucleophilic substitutions of the benzene ring proceed with aromatic amines and alcohols under mild conditions. The attack of aliphatic amines may be directed to the aromatic core as well as to the carbonyl unit leading to azocarboxamides. The benzene ring can further be modified through radical reactions, in which the tert-butyloxycarbonylazo group enables the generation of aryl radicals at either elevated temperatures or under acidic conditions. Radical reactions include oxygenation, halogenation, carbohalogenation, carbohydroxylation, and aryl-aryl coupling.     

Some Applications to Variational–Hemivariational Inequalities of the Principle of Symmetric Criticality for Motreanu–Panagiotopoulos Type Functionals

Using the principle of symmetric criticality for Motreanu–Panagiotopoulos type functionals we give some existence and multiplicity results for a class of variational–hemivariational inequalities on ^L+M .This work was partially supported by MEdC-ANCS, research project CEEX 2983/11.10.2005.     

Determination of Particle Size Distribution and Electrokinetic Properties with the AcoustoSizer in Comparison with Other Methods

The characterization of suspensions in process concentration is an important task for the optimization of handling and product properties. Only very few instruments are available. The AcoustoSizer (ACS) (Colloidal Dynamics PTY Ltd.) uses the so-called electrokinetic sonic amplitude (ESA) for particle size and zeta potential determination. In this work, the results obtained at moderate concentrations were compared with results of other instruments mostly working with dilute suspensions. For the electrokinetic investigations three methods (beside the ACS) were used: electroacoustics (ESA8000, Matec Applied Sciences), microelectrophoresis (Zetamaster, Malvern Instruments) and streaming current measurements (Particle Charge Detector PCD 03-pH, Miitek). For particle size determination different measuring techniques were applied: laser diffraction spectroscopy (Mastersizer S, Malvern Instruments), dynamic light scattering (Ultra Fine Particle Analyser, Leeds and Northrup), sedimentation analysis (Sedigraph 5000 D, Micromeritics) and scanning electron microscopy. Mainly three powders were used in the investigations: Monospher M1200 silica (Merck), Selectipur titania (Merck) and Aluminiumoxid C alumina (Degussa). The agreement between the different methods for both particle size and zeta potential measurements was excellent. Especially for the electrokinetic investigations, careful sample preparation is needed. The procedure must not change the equilibria determining the physical and chemical state of the suspension.     

NITRATE EFFECT ON Pfr-MEDIATED AND GA3-INDUCED GERMINATION IN SPORES OF Anemia phyllitidis (L.) Sw*

Spore germination in Anemia phyllitidis can be induced by red light (R) via the phytochrome system and by gibberellic acid (GA₃) in the dark. An enhancing effect of NO₃-ions on the Pfr-mediated germination could be demonstrated. This NO₃-effect was found to be pronounced during the preinduction phase and could be described by biphasic kinetics depending on the formation of Pfr by the R-irradiation. Besides NO₃, other electron accepting substances also increased germination significantly. In contrast to Pfr-mediated germination, no enhancing effect by NO₃ could be obtained for the GA₃-induced germination response. The application of an inhibitor of gibberellic acid synthesis, AMO1618, as well as the analysis of combined R and GA₃ treatment, support the hypothesis that for germination of Anemia phyllitidis spores no synergism between the factors exists. Thus, it is proposed that the gibberellic acid receptor starts a signal-transduction pathway resulting in germination which is in part independent of the Pfr-mediated signal-transduction chain. The NO₃-effect is specific for the Pfr-mediated signal-transduction chain.     

Apparently complex high-pressure phase of gallium as a simple modulated structure

The phase of gallium GaII, with symmetry C222(1) and 104 atoms per unit cell, has been recently reported as an example of structural complexity under high pressure. It is shown here that this phase is a simple modulated distortion of an average structure of Fddd symmetry with all atoms structurally equivalent. The modulation can be described with only 4 parameters and satisfies symmetry properties described by a centrosymmetric superspace group. The structural distortion is dominated by a frozen transversal mode associated with a single irreducible representation of Fddd, with a wave vector on the line Q, at an edge of the Brillouin zone. The average structure can be related with an hcp configuration through simple sliding of hcp layers, reminiscent of the hcp-bcc Bürgers mechanism.