Partial synthesis of 23-hydroxyursolic acid isolated from medicinal plants of the Rubiaceae family

23-Hydroxyursolic acid (2), previously isolated from medicinal plants of the Rubiaceae family, was synthesized in ten steps via methyl 23-hydroxy-3-oxours-12-en-28-oate (5) from commercially available ursolic acid (6).     

3-Trifluoromethyl- and 3-difluoromethyl-thalidomides

Syntheses of racemic 3-trifluoromethyl- and 3-difluoromethyl-thalidomide starting from 2-(tert-butyloxycarbonylimino)-3,3,3-trifluoropropionate or -3,3-difluoropropionate as fluorine-containing building blocks are described.     

Studies on the Synthesis of Trisaccharide Analogues of the Antibiotic Moenomycin A

A new approach for the synthesis of moenomycin trisaccharide analogues is reported in which three monosaccharide building blocks are used and allows the introduction of different substituents at the 6‐position of unit E (Scheme 2). Furthermore, a new procedure for the introduction and manipulation of unit F is described (Scheme 3).     

Supramolecular recognition and structural elucidation of inclusion complexes of an achiral carbene precursor in beta- and permethylated beta-cyclodextrin

[structure: see text] Inclusion of achiral carbene precursor endo-8-azibicyclo[3.2.1]octan-3-ol (1) in chiral beta-cyclodextrin (7-Cy) and tri-O-methyl-beta-cyclodextrin (TRIMEB) leads to 1:1 complexes 1@7-Cy and 1@TRIMEB, respectively. The combined methods of induced circular dichroism, NMR spectroscopy, and X-ray structure determination were employed for the first time for structural elucidation of the complexes in solution and the solid state. Significantly different orientations of 1 were observed. Compared with 1@7-Cy, 1@TRIMEB exhibits a different guest orientation and an association constant one-twentieth lower.     

Kinetik der unkatalysierten Urethanbildung

Summary The kinetics of the reaction of phenylisocyanate with 1-butanol have been studied at low concentrations in carbon tetrachloride solution at three temperatures. The present paper describes the relation between the reaction rate and the concentration of the alcohol dimer and the 1:1 alcoholurethane associate. Therefrom we conclude that the monomeric alcohol does not play any significant part in the reaction. We explain the observed rate equation with the second-order term of the reactants with the equality of the productsk _AA K _AA andk _AU K _AU (rate constant and association constant of alcohol dimer and 1:1 alcohol-urethane associate).For the reaction of alcohol dimer H =45.4 kJ mol^–1 and S =– 142J mol^–1K^–1. We interpret this result in terms of a six-cyclic transition state.

     

Phototransformation of monovinyl and divinyl protochlorophyllide by NADPH:Protochlorophyllide oxidoreductase of barley expressed in Escherichia coli

The chlorophyll precursors monovinyl protochlorophyllide (MV-PChlide) and divinyl protochlorophyllide (DV-PChlide) were extracted from mutant C-2A' of the unicellular green alga Scenedesmus obliquus which accumulates both protochlorophyllide derivatives in the dark. The two pigments were characterized by absorption and fluorescence spectroscopy and by plasma desorption mass spectrometry. The molecular masses of MV-PChlide and DV-PChlide were determined as 612 and 610 atomic mass units (amu) respectively. Both MV-PChlide and DV-PChlide were accepted as substrates and photoconverted to chlorophyllides in vitro by NADPH:protochlorophyllide oxidoreductase of barley expressed in Escherichia coli.     

Bestimmung der Atomladungen in Molekülen aus der Verschiebung der K α1/α2-Hauptlinie und ihrer Satellitenlinien für Elemente der 3.Periode

Zusammenfassung Mit einem quantenmechanischen Variationsverfahren werden unter Verwendung eines minimalen Basissatzes an STO-Funktionen für die Elemente der 3. Periode: Mg, Al, Si, P die Verschiebungen der K _1/2-Hauptlinie und ihrer Satellitenlinien , , ₃, ₃, ₄ als Funktion des Ionisationsgrades berechnet. Durch Vergleich mit der experimentell bestimmten Verschiebung des K -Satellitenspektrums in Verbindungen lassen sich Informationen über die Elektronenverteilung in der Umgebung dieser Elemente gewinnen. Aus der Verschiebung werden schließlich die effektiven Atomladungen der Elemente in den betreffenden Verbindungen bestimmt.

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Determination of the atomic charges of the 3rd period elements in molecules by means of the displacements of the K -satellites

STO-Calculations are reported for X-ray-transitions of the type K ¹ L ¹L ² for the 3rd period elements Mg, Al, Si, P and some of their ions. Moreover the shift of the K _1/2-satellites as a function of the degree of ionization is compared with the experimental displacements in certain compounds of 3rd period elements. In this way some information results about the electron distribution in the neighbourhood of the emitting atom. We relate the shift to the number of electrons in the outer shell of the atom and determine the effective charges of 3rd period elements in compounds.

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Résumé Calculs STO pour les transitions du spectre X de type K ¹ L ¹L ² pour les éléments de la troisième période Mg, Al, Si, P et certains de leurs ions. De plus le déplacement des satellites K _1/2-en fonction du degré d'ionisation est comparé avec les déplacements expérimentaux dans certains composés des éléments de la troisiéme période. De cette manière on obtient une certaine information sur la distribution électronique au voisinage de l'atome émetteur. Nous relions le déplacement au nombre d'électrons dans la couche externe de l'atome et nous déterminons les charges effectives des éléments de la troisiéme période dans leurs composés.

     

Über Halogenotitanate(IV)

The preparation of tetraethylammonium slats with following anions is described: [TiBrCl₅]^2?,[TiBr₅Cl]^2?,[TiCl₄Br · CH₃CN]^?, [TiBr₄Cl · CH₃CN]^?, [TiBr₅ · CH₃CN]^? und TiF. The reaction mechanisms is discussed. TiF forms fluorine-bridges giving a polymeric anion. Chlorofluorotitanates(IV) could not be prepared. Mixed halide complexes of Ti(IV), Nb(V) and Ta(V) are compared with analogous complexes of Sn(IV), Pb(IV) and Sb(V).     

Ring transformations of heterocyclic compounds. XXII. Pyrido[1,2‐a]indolium salts from 2‐methyl‐3H‐indoles by pyrylium mediated three carbon annelation

The synthesis of pyrido[1,2‐a]indolium perchlorates 8,11 from 2,4,6‐triarylpyrylium perchlorates 1 and 2‐methyl‐3H‐indoles 6,9 in the presence of a basic condensing agent (anhydrous sodium acetate, piperidine acetate, triethylamine/acetic acid, triethylamine) in ethanol by a 2,4‐[C₃+C₂N] pyrylium ring transformation is reported. Spectroscopic data of the transformation products and their mode of formation are discussed.     

Novel DOTA-based prochelator for divalent peptide vectorization: synthesis of dimeric bombesin analogues for multimodality tumor imaging and therapy

Dimeric peptidic vectors, obtained by the divalent grafting of bombesin analogues on a newly synthesized DOTA-based prochelator, showed improved qualities as tumor targeted imaging probes in comparison to their monomeric analogues.