Two synthetic approaches to rebeccamycin

Two synthetic approaches to a new indolocarbazole antitumor antibiotic, rebeccamycin, were developed. The absolute configuration of rebeccamycin was determined by a total synthesis.     

Enzymatic synthesis of 7-deoxy-N-acetylneuraminic acid and 7-O-methyl-N-acetylneuraminic acid

7-Deoxy-N-acetylneuraminic Acid and 7-O-methyl-N-acetylneuraminic acid were synthesized through the sialic acid aldolase-catalyzed aldol addition reactions of 4-deoxy-N-acetyl-D-mannosamine and 4-O-methyl-N-acetyl-D-mannosamine, respectively, with pyruvate. The obtained sialic acids will be used as probes for the investigation of the unusual mechanism of a novel sialidase from leech.     

Dilute sulfuric acid pretreatment of corn stover at high solids concentrations

Applied Biochemistry and Biotechnology - The enzymatic digestibility of a pretreated substrate is enhanced by increasing the severity of the pretreatment conditions, apparently because a greater...     

Comparison of fluorimetric methods of assay for 7 H-Benz(de)anthracen-7-one in airborne particulates and air pollution source effluents

Summary Various modifications of a thin-layer chromatography fluorimetric method for the determination of 7 H-benz(de)anthracen-7-one (BO) and phenalen-1-one (PO) in complex mixtures have been compared. The best modifications consisted of one-dimensional thin-layer chromatography followed by elution, evaporation, solution in trifluoroacetic acid, followed by either spectrophotofluorimetric or fluorimetric assay. In some cases a quenching agent was necessary to quench the fluorescence of the interferences. Urban atmospheres and air pollution source effluents can be analyzed by these micromethods. These methods with slight modification could be applied to the determination of the aza heterocyclic and the other ring-carbonyl compounds found in urban atmospheres and air pollution source effluents.

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Zusammenfassung Verschiedene Modifikationen einer dünnschichtchromatographischen, fluorimetrischen Methode zur Bestimmung von 7 H-Benz(de)-anthracen-7-on (BO) und Phenalen-1-on (PO) in komplexen Gemischen wurden verglichen. Am besten bewährte sich eindimensionale Dünnschichtchromatographie, nachfolgende Elution, Abdampfen, Aufnehmen in Trifluoressigsäure und schließlich Bestimmung durch Spektralfluoreszenz-oder Fluoreszenzmessung. In manchen Fällen war es nötig, die Fluoreszenz störender Substanzen mit einem geeigneten Reagens zu löschen. Stadtatmosphäre oder Quellen der Luftverunreinigung können mit diesen Mikromethoden analysiert werden. Sie eignen sich nach geringfügiger Modifikation auch zur Bestimmung von azaheterocyklischen und anderen Ring-Carbonylverbindungen in der Atmosphäre.

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Résumé On a comparé entre elles différentes modifications d'une méthode de fluorimétrie avec chromatographie en couche mince pour le dosage de la benzo-7 H anthracène-one-7 (BO) et de la phénalène-one-1 (PO) en mélanges complexes. Les modifications les meilleures ont consisté en une Chromatographie en couche mince unidimensionnelle suivie d'élution, évaporation, mise en solution dans l'acide trifluoroacétique, opérations suivies d'une recherche spectrophotofluorimétrique ou fluorimétrique. Dans certains cas, un agent d'extinction s'est montré nécessaire pour éteindre la fluorescence due aux interférences. On peut analyser par ces microméthodes les atmosphères urbaines et les écoulements sources de pollution de l'air. Ces méthodes ont pu être appliquées après légère modification au dosage des composés aza hétérocycliques et autres composés carbonyles cycliques trouvés dans les atmosphères urbaines et dans les écoulements sources de pollution de l'air.

     

The isolation and structure determination of cryptomisrine,a novel indolo[3,2-b]quinoline dimeric alkaloid from cryptolepis sanguinolenta

The isolation and structure determination of cryptomisrine, a novel indolo[3,2-b]quinoline dimeric alkaloid obtained from extracts of the roots of the Ghanaian medicinal plant Cryptolepis sanguinolenta is reported. The structure determination was made via a consideration of the spectral data, including uv, ir, nmr, and mass spectra. In particular, one-dimensional proton/carbon nmr, one-dimensional nOe difference nmr, and a series of homonuclear (COSY) and inverse-detected heteronuclear two-dimensional (HMQC, HMBC) experiments were utilized, as well as high resolution FABMS. Cryptomisrine is most unusual in that its two monomeric parts apparently exist in such a C₂ symmetric environment that only one set of proton and carbon nmr resonances are observed. Cryptomisrine is the first example of a dimeric indolo-[3,2-b]quinoline alkaloid to have been isolated from nature.     

Lamellar Organo-Bridged Silicones

The acid-hydrolysis of an organo-bridged bisdiethoxysilylated molecular precursor bearing urea groups, (EtO)₂MeSi(CH₂)₃NHCONH(CH₂)₁₂NHCONH(CH₂)₃SiMe(OEt)₂, has been performed in pure aqueous medium. Scanning electron microscopy (SEM) analysis of the resulting insoluble solid revealed plate-like forms with a lamellar structure as determined by powder X-ray diffraction (PXRD) studies with a sharp peak at 28.5 Å. The solid state ²⁹Si MAS-NMR spectrum of this bridged siloxane hybrid is consistent with a moderately condensed material with complete preservation of the Si–C bonds throughout the hybrid network. In comparison, the classical sol–gel hydrolysis-condensation of the molecular precursor in ethanol with stoichiometric amount of water and fluoride anion as catalyst produced an amorphous featureless solid.