The stereoselectivity of ketal Claisen rearrangements with ketals of simple cyclic ketones

Claisen rearrangements of the ketals of cyclopentanone, cyclohexanone and cycloheptanone give mixtures of and products favoring the isomer by as much as 19:1. The selectivity is attenuated by enolization processes in the 5- and 6-membered ring systems.     

Generation of antiserum to Irgarol 1051 and development of a sensitive enzyme immunoassay using a new heterologous hapten derivative

A polyclonal antiserum to Irgarol 1051 was developed in sheep and used to construct an enzyme immunoassay method for the measurement of the antifouling compound in river and seawater samples. The antiserum was generated by a hapten derivative, 2-(tert-butylamino)-4-(cyclopropylamino)-6-(thiopropionic acid)-1,3,5-triazine, coupled to a mixture of keyhole limpet hemocyanin and bovine serum albumin, and the competitive enzyme immunoassay was constructed using a plate-coating antigen made of a heterologous new hapten derivative, 2-(tert-butylamino)-4-(cyclopropylamino)-6-(phenoxybenzoic acid)-1,3,5-triazine, linked to gelatine. The assay showed a sensitivity of about 5 ng L^–1 in river and seawater matrices with reasonable specificity with respect to commonly used triazines such as atrazine (3%), simazine (>0.1%) and desethylatrazine (>0.01%). However, high cross-reactivity levels were found with ametryn (56%) and prometryn (60%). Tests on the effects of organic solvents on assay performance indicated a high tolerance to methanol but much less so to acetonitrile. The assay was found to be highly reproducible and robust owing to the stability of the sheep antibody and the highly optimised competitive assay reagents which included the use of the new triazine-O-phenoxybenzoic acid derivative.     

Mesoporous zirconium titanium oxides. Part 1: Porosity modulation and adsorption properties of xerogels

A series of zirconium titanium oxide mesophases containing 33 atom % Zr have been prepared using carboxylic acids of different alkyl chain lengths (Cy ) from y=4-18 through organic-inorganic polymer phase segregation as the gel transition is approached. Thermal treatment of these transparent gels up to 450 degrees C eliminated the organic template, and domain coarsening occurred affording stable worm-hole mesoporous materials of homogeneous composition and pore diameters varying from about 3 to 4 nm in fine increments. With such materials, it was subsequently possible to precisely study the adsorption of vanadium oxo-anions and cations from aqueous solutions and, more particularly, probe the kinetics of intraparticle mass transport as a function of the associated pore dimension. The kinetics of mass transport through the pore systems was investigated using aqueous vanadyl (VO2+) and orthovanadate (VO3(OH)2-) probe species at concentrations ranging from 10 to 200 ppm (0.2 to 4 mmol/L) and pH values of 0 and 10.5, respectively. In the case of both of these vanadium species, the zirconium titanate mesophases displayed relatively slow kinetics, taking in excess of about 500 min to achieve maximum uptake. By using a pseudo-second-order rate law, it was possible to extract the instantaneous and overall rate of the adsorption processes and then relate these to the pore diameters. Both the instantaneous and overall rates of adsorption increased with increasing surface area and pore diameter over the studied pore size range. However, the equilibrium adsorption capacity increased linearly with pore diameter only for the higher concentrations and was independent of pore diameter for the lower concentration. These results have been interpreted using a model in which discrete adsorption occurs at low concentrations and is then followed by multilayer adsorption at higher concentration.     

Biochemical and structural insights of the early glycosylation steps in calicheamicin biosynthesis

The enediyne antibiotic calicheamicin (CLM) gamma(1)(I) is a prominent antitumor agent that is targeted to DNA by a novel aryltetrasaccharide comprised of an aromatic unit and four unusual carbohydrates. Herein we report the heterologous expression and the biochemical characterization of the two "internal" glycosyltransferases CalG3 and CalG2 and the structural elucidation of an enediyne glycosyltransferase (CalG3). In conjunction with the previous characterization of the "external" CLM GTs CalG1 and CalG4, this study completes the functional assignment of all four CLM GTs, extends the utility of enediyne GT-catalyzed reaction reversibility, and presents conclusive evidence of a sequential glycosylation pathway in CLM biosynthesis. This work also reveals the common GT-B structural fold can now be extended to include enediyne GTs.     

An integrated method for metabolite detection and identification using a linear ion trap/Orbitrap mass spectrometer and multiple data processing techniques: application to indinavir metabolite detection

A new strategy using a hybrid linear ion trap/Orbitrap mass spectrometer and multiple post-acquisition data mining techniques was evaluated and applied to the detection and characterization of in vitro metabolites of indinavir. Accurate-mass, full-scan MS and MS/MS data sets were acquired with a generic data-dependent method and processed with extracted-ion chromatography (EIC), mass-defect filter (MDF), product-ion filter (PIF), and neutral-loss filter (NLF) techniques. The high-resolution EIC process was shown to be highly effective in the detection of common metabolites with predicted molecular weights. The MDF process, which searched for metabolites based on the similarity of mass defects of metabolites to those of indinavir and its core substructures, was able to find uncommon metabolites not detected by the EIC processing. The high-resolution PIF and NLF processes selectively detected metabolites that underwent fragmentation pathways similar to those of indinavir or its known metabolites. As a result, a total of 15 metabolites including two new indinavir metabolites were detected and characterized in a rat liver S9 incubation sample. Overall, these data mining techniques, which employed distinct metabolite search mechanisms, were complementary and effective in detecting both common and uncommon metabolites. In summary, the results demonstrated that this analytical strategy enables the high-throughput acquisition of accurate-mass LC/MS data sets, comprehensive search of a variety of metabolites through the post-acquisition processes, and effective structural characterization based on elemental compositions of metabolite molecules and their product ions.     

Mizellare Wechselwirkung und ihre katalytische Rolle bei der Polymerisation von Acrylamid, die durch Bisulfit katalysiert wird

Ohne Zusammenfassung     

Isotopenaustausch von molekularem Sauerstoff mit dem Sauerstoff von Ni-Molybdat

Ohne Zusammenfassung