Total synthesis of (3S,4S,2′S)- and (3R,4R,2′S)-viridiofungin A triester

The total synthesis of an alkylcitrate secondary metabolite from the fungi Trichoderma viride is described. An ester dienolate [2,3]-Wittig rearrangement and a S. Julia-Kocienski olefination served as key C/C-connecting transformations. The highly convergent synthesis consists of a longest linear sequence of 17 steps.     

Synthesis of enantiopure axially chiral C3-symmetric tripodal ligands and their application as catalysts in the asymmetric addition of dialkylzinc to aldehydes

The enantioselective synthesis of a novel-type C(3)-symmetric tripodal ligand that is composed of a central mesitylene-derived core and three functionalized, axially chiral biaryl subunits is described. The triol (M,M,M)-3 is a suitable catalyst for the enantioselective addition of dialkylzinc to various aromatic aldehydes with asymmetric inductions of up to 98% ee.     

Nuclear amination catalyzed by fungal laccases: reaction products of p-hydroquinones and primary aromatic amines

[reaction: see text] Nuclear amination of p-hydroquinones with primary aromatic amines was catalyzed by fungal laccases (EC 1.10.3.2) from Trametes spec. and Myceliophthora thermophila. This is the first report of laccase-catalyzed synthesis of aminoquinones. Incubation of two compounds with laccase in the presence of oxygen resulted in the formation of the corresponding monoaminated or diaminated quinones. No hydroquinonoids were formed. Observed differences in the reaction courses for different p-hydroquinones and aromatic amines with different laccases are discussed.     

Quantitative Felddesorptions-Massenspektrometrie. II

Zusammenfassung Die Molekülionen von Gemischen polycyclischer Kohlenwasserstoffe wurden auf der Photoplatte eines hochauflösenden Felddesorptions-Massenspektrometers registriert. Die erhaltenen Schwärzungsintensitäten wurden mit der relativen Konzentration der eingesetzten Mischungskomponenten verglichen. Proben im Mikrogrammbereich ergaben Abweichungen von etwa ± 5%.Wir danken Herrn Dr. H. Güsten, Karlsruhe, für die uns zur Verfügung gestellten polycyclischen Kohlenwasserstoffe und Herrn Dr. W. D. Lehmann für wertvolle Diskussionen. Der Deutschen Forschungsgemeinschaft, dem Ministerium für Wissenschaft und Forschung des Landes Nordrhein-Westfalen sowie dem Fonds der chemischen Industrie danken wir für die finanzielle Unterstützung.     

Characterisation of humic substances using atmospheric pressure chemical ionisation and electrospray ionisation mass spectrometry combined with size-exclusion chromatography

Humic substances were analysed by atmospheric pressure chemical ionisation (APCI) and electrospray ionisation (ESI) mass spectrometry in positive and negative modes. Using APCI the average m/z range of humic substances was reduced 5-fold compared to ESI. High-resolution time-of-flight mass spectrometry revealed the formation of multiply charged molecules in the ESI mode. Moreover, it was possible to obtain daughter ion mass spectra of humic substances by nanospray tandem mass spectrometry. The size-exclusion chromatography elution profile of humic substances was highly influenced by the pH of the analyte solution. By contrast, the pH had no significant influence on the observed mass spectra of humic substances.     

Über die Extrahierbarkeit des Wolfram(VI)-rhodanids

Zusammenfassung Die Anwendbarkeit des Wolfram(VI)-komplexes mit Rhodanid für die analytische Praxis wurde untersucht; durch seine Löslichkeit in organischen Lösungsmitteln eignet sich der Komplex gut zur Trennung von anderen Elementen.Unter Zuhilfenahme des radioaktiven Wolframisotopes¹⁸⁵W konnten die optimalen Extraktionsbedingungen, wie Säure- und Rhodanidkonzentration, rasch ermittelt werden. Bei der Untersuchung verschiedener organischer Lösungsmittel zeigte Amylalkohol sowohl in reiner Form als auch in Mischungen mit Chloroform die besten Extraktionseigenschaften.Da der Komplex zu den stärksten des Wolframs gehört, stören bei der Durchführung von Analysen nur wenige Anionen, am meisten Fluorid. Von den Kationen werden nach Reduktion des Eisens, wozu Ascorbinsäure empfohlen wird, nur wenige andere mitextrahiert; am störendsten wirkt Molybdän, das mitausgeschüttelt wird und anschließend entfernt werden muß. Zur Bestimmung des Wolframs eignet sich dann am besten die Hydrochinonmethode.

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Summary A study was made of the use of tungsten(VI) complex with thiocyanate in analytical practice. Because of its solubility in organic liquids the complex is well suited for separation from other elements.By using the radioactive isotope¹⁸⁵W, the optimal extraction conditions, such as the acid- and thiocyanate concentration, could be rapidly determined. When various organic solvents were tried, it was found that amyl alcohol, either by itself or mixed with chloroform, had the best extraction characteristics.Since the complex is one of the most stable formed by tungsten, only a few anions interfere in the analysis; fluoride causes the most trouble. Among the cations, only a few interfere after the iron has been reduced (ascorbic acid is recommended for this purpose). The greatest interference comes from molybdenum, which is co-extracted and has to be removed subsequently. The hydroquinone method is then the best procedure for determining the tungsten.

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Résumé On a cherché à appliquer le complexe tungstène-VI-thiocyanate à l'analyse. Grâce à sa solubilité dans les solvants organiques, le complexe se prête bien à la séparation d'avec les autres éléments.Au moyen de l'isotope radioactif du tungstène¹⁸⁵W, on a pu trouver rapidement les conditions optimales d'extraction, ainsi que la concentration en acide et en thiocyanate. Après essai de divers agents de dissolution organiques, l'alcool amylique a montré les meilleures propriétés extractives, aussi bien sous sa forme pure qu'en mélange avec le chloroforme.Etant donné que le complexe est l'un des plus robustes du tungstène, seuls quelques anions gênent pour effectuer les analyses, et surtout les fluorures. Parmi les cations, après réduction du fer pour laquelle l'acide ascorbique est recommandé, seuls quelques autres sont extraits avec lui; le molybdène présente l'action la plus gênante, il doit être masqué et séparé complètement. Pour le dosage du tungstène, la méthode à l'hydroquinone convient alors le mieux.

     

Structural transitions as determinants of the action of the calcium-dependent antibiotic daptomycin

Daptomycin is a cyclic anionic lipopeptide antibiotic recently approved for the treatment of complicated skin infections (Cubicin). Its function is dependent on calcium (as Ca2+). Circular dichroism spectroscopy indicated that daptomycin experienced two structural transitions: a transition upon interaction of daptomycin with Ca2+, and a further transition upon interaction with Ca2+ and the bacterial acidic phospholipid, phosphatidyl glycerol. The Ca2+-dependent insertion of daptomycin into model membranes promoted mild and more pronounced perturbations as assessed by the increase of lipid flip-flop and membrane leakage, respectively. The NMR structure of daptomycin indicated that Ca2+ induced a conformational change in daptomycin that increased its amphipathicity. These results are consistent with the hypothesis that the association of Ca2+ with daptomycin permits it to interact with bacterial membranes with effects that are similar to those of the cationic antimicrobial peptides.