Synthesis of an N-Acetylated Heparin Pentasaccharide and its anticoagulant activity in comparison with the heparin pentasaccharide with high anti-factor-Xa activity

The synthesis of tri-N-acetylated heparin pentasaccharide 2 is described. It was assembled from five suitably blocked monosaccharide units ( 3 – 7 ). Glucuronic-acid building block 4 was prepared from glucose by direct Jones oxidation of the 6-O-trityl derivative 18 . The resulting acid 16 was esterified to 17 in large mounts using methyl chloroformate/base. Trimethylsilyl bromide proved to be an excellent reagent for the hydrolysis of a prop-1-enyl glycoside ( 19 →21 ). The pentasaccharide 29 was obtained by a [2 + 2] + 1 synthesis, the glycosylation reactions furnished good to very good yields. The identity of protected oligosaccharides was confirmed by ¹H-NMR spectroscopy. Sequential deblocking of the pentasaccharide, O-sulfation, and N-acetylation gave 2 which was shown to exhibit ca. 600 times lower anticoagulant activity than pentasaccharide 1 .     

The cosmology of the nonsymmetric theory of gravitation

We show that during cosmological inflation the nonsymmetric metric tensor theory of gravitation develops a spectrum which is potentially observable by cosmic microwave background observations, and may be the most sensitive probe of the scale of cosmic inflation.     

Ab Initio Thermochemistry of Solid‐State Materials

In this contribution we introduce an electronic‐structure‐theory‐based approach to a quantum‐chemical thermochemistry of solids. We first deal with local and collective atomic displacements and explain how to calculate these. The fundamental importance of the phonons, their dispersion relations, their experimental determination as well as their calculation is elucidated, followed by the systematic construction of the thermodynamic potentials on this basis. Subsequently, we provide an introduction for practical computation as well as a critical analysis of the level of accuracy obtainable. We then show how different solid‐state chemistry problems can be solved using this approach. Among these are the calculation of activation energies in perovskite‐like oxides, but we also consider the use of theoretical vibrational frequencies for determining crystal structures. The pressure and temperature polymorphism of elemental tin which has often been classically described is also treated, and we energetically classify the metastable oxynitrides of tantalum. We also demonstrate, using the case of high‐temperature superconductors, that such calculations may be used for an independent evaluation of thermochemical data of unsatisfactory accuracy. Finally, we show the present limits and the future challenges of the theory.     

Zur Synthese von Imidazo(2,1-b)-1,3,4-thiadiazolo(3,2-a)-pyrimidonen-(6)

2-Amino-6-aryl-imidazo(2,1-b)-1,3,4-thiadiazoles (1 a-f) were condensed with 1,3-ketocarboxylates e. g. ethyl-butyroacetate, ethyl-benzoylacetate, 4-nitrobenzoylacetate or ethyl-cyclopentanone(2)-carboxylate and ethyl-cyclohexanone(2)-carboxylate directly to imidazo(2,1-b)-1,3,4-thiadiazolo(3,2-a) pyrimidones-(6) (4 a-f, 5 a-f, 6 d, e, 7 a-f, 8 a, d).

11. Mitt. über Heterocyclen; 10. Mitt.Paul, H., Sitte, A., Wessel, R., Arch. Pharm. (Weinheim), im Druck.     

The temperature dependence of the exchange reaction between oxygen atoms and dioxygen molecules studied by means of isotopes and spectroscopy

The temperature dependence of the rate constant for the exchange reaction between oxygen atoms and dioxygen molecules has been studied using the oxygen isotopes ¹⁶O and ¹⁸O. The reaction was studied by VIS-photolysis of ozone in the presence of isotopic dioxygen and with nitrogen as a bath gas at five different temperatures, 143 K, 173 K, 203 K, 253 K, and 295 K. High-resolution microwave spectroscopy was used to measure the composition of the ozone isotopomer mixtures and mass-spectrometry was used to determine the abundances of the isotopomeric dioxygen species formed during the reaction. The rate constant was determined to be k_exchange=(2.66±0.78)×¹⁰⁻¹² (T/300 K)^{−(0.88±0.26)} cm³s⁻¹ (±2σ ) or as the ratio between rate constants for exchange and for ozone formation, (4.67±1.3)×10²¹ (T/300 K)^(1.74±0.19) cm⁻³ (±2σ). © 1997 John Wiley & Sons, Inc.     

Formation of Adamantane-Like Structures by Reaction of Titanocene Fluorides with an Iminoalane

Fluorine–nitrogen metathesis in the reaction of a cyclic iminoalane with titanocene fluorides results in unexpected cage compounds. Treatment of one of these compounds with diethyl ether leads to 1 , which contains a titanium–nitrogen double bond stabilized intramolecularly by fluorine.