Voltammetric monitoring of laccase-catalysed mediated reactions

Six different compounds capable of mediating laccase-catalysed reactions have been tested by cyclic voltammetry. They exhibited quasi-reversible electrodic behaviour with formal redox potentials ranging from 150 to 800 mV (E(0)' vs. SCE). The immersion of a laccase-coated glassy carbon electrode (GCE) in mediator solutions generated large cathodic catalytic currents easily recorded by cyclic voltammetry at low-potential scan rates. This current showed two well-defined pH profiles, which correlated with the variation of the mediator redox potentials at the pH range tested. The relevant effect of temperature on the activity of laccase has been assessed here. Likewise, it was shown that the current record varied with the substrate concentration. This trend fitted Michaelis-Menten kinetics, which allowed us to give an estimation of the affinity of the fungal laccase for the different mediators.     

A facile synthesis of novel triazoloquinoxahnones and triazinoquinoxalinones

A series of 1-aryl-s-triazolo[4,3-a]quinoxalin-4-ones, 3 , were synthesized via the pyrolysis of the corresponding hydrazones, 6 . Thus, the cyclodehydrogenation occurred by refluxing them in an inert solvent (e.g. ethylene glycol) to give the triazoloquinoxalin-4-ones in a satisfactory yield. Using DMSO as a solvent for the above transformation afforded as a minor by-product an S-ylid. In contrast to earlier findings, annelation of a six-membered ring was successful and achieved through the pyrolysis of the pyruvate hydrazones derived of the quinoxalin-4-ones at ?230° to give the as-triazino[4,3-a]quinoxalin-5-ones, 4 . The reaction of 5 with acetylacetone afforded 3-(3′,5′-dimethylpyrazol-1-yl)-2(1H)-quinoxalinone, 10 . The structural assignments for the new compounds were based on their elemental analysis and spectroscopic data as well as an independent synthesis.     

Alstonia scholaris: Struktur des Indolalkaloides Narelin

Alstonia scholaris: The structure of the indole alkaloid nareline Besides the known akuammidine, picralinal, picrinine and pseudoakuammigine a new indole alkaloid called nareline (M=352) was isolated from Alstonia scholaris R. BR. , which belongs to the plant family of Apocynaceae. Its structure 2 was deduced by single crystal X-ray diffraction. 2 represents the absolute configuration. The spectroscopic data of 2 and its derivatives (Scheme 1) as well as their chemical behavior support this structure. In biogenetic sense nareline is related to the bases akuammiline ( 4 ) and picraline ( 5 ) (Scheme 2). In contrast to those the C-atom 5 is exocyclic and represents an aldehyde group which forms together with the oxygen atom of the N (4)-hydroxylamine group a cyclic half acetale. - By oxidation (CrO₃/CH₃COOH) of 2 the oxindol derivative 19 (oxonareline) is formed which contains a cyclic acetal as a partial structure element (Scheme 4).     

Design and parallel solid-phase synthesis of ring-fused 2-pyridinones that target pilus biogenesis in pathogenic bacteria

A new method for the solid-phase synthesis of enantiomerically enriched highly substituted ring-fused 2-pyridinones 13 has been developed. The synthesis mediates introduction of substituents at two positions in the 2-pyridinone ring in a diverse manner and is suitable for parallel synthesis. (19)F NMR spectroscopy was used as a tool to monitor each of the five steps in the reaction sequence. The optimized conditions thus obtained were then used to prepare a library of 20 2-pyridinones with high yields. The library members were chosen from a statistical multivariate design to ensure diversity and reliable data for structure-activity relationships. Screening of the library against the bacterial periplasmic chaperone PapD was performed using surface plasmon resonance. Three new 2-pyridinones with a higher affinity for the chaperone PapD than the previous best 13[10,1] were found, and important structural features could be deduced.     

Screening,library-assisted identification and validated quantification of fifteen neuroleptics and three of their metabolites in plasma by liquid chromatography/mass spectrometry with atmospheric pressure chemical ionization

A liquid chromatographic/mass spectrometric assay with atmospheric pressure chemical ionization (APCI-LC/MS) is presented for the fast and reliable screening and identification and for the precise and sensitive quantification of 15 neuroleptic (antipsychotic) drugs and three of their relevant metabolites in plasma. It allows confirmation of the diagnosis of a neuroleptic overdose and monitoring of psychiatric patients' compliance. The neuroleptics amisulpride, bromperidol, clozapine, droperidol, flupenthixol, fluphenazine, haloperidol, melperone, olanzapine, perazine, pimozide, risperidone, sulpiride, zotepine and zuclopenthixol and the pharmacologically active metabolites norclozapine, clozapine N-oxide and 9-hydroxyrisperidone were extracted from plasma using solid-phase extraction and were separated on a Merck LiChroCART column with Superspher 60 RP Select B as the stationary phase. Gradient elution was performed using aqueous ammonium formate and acetonitrile. After screening and identification in the scan mode using the authors' new LC/MS library, the neuroleptics were quantified in the selected-ion mode. The quantification assay was fully validated. It was found to be selective and proved to be linear from sub-therapeutic to over therapeutic concentrations for all analytes. The corresponding reference levels are listed. The accuracy and precision data were within the required limits. The analytes were stable in frozen plasma for at least 1 month. The method was successfully applied to several authentic plasma samples from patients treated or intoxicated with various neuroleptics. The validated LC/MS assay has proved to be appropriate for the isolation, separation, screening, identification and quantification of various neuroleptics in plasma for clinical toxicology and therapeutic drug monitoring purposes.     

Morphology-controlled nonaqueous synthesis of anisotropic lanthanum hydroxide nanoparticles

The preparation of lanthanum hydroxide and manganese oxide nanoparticles is presented, based on a nonaqueous sol-gel process involving the reaction of La(OiPr)₃ and KMnO₄ with organic solvents such as benzyl alcohol, 2-butanone and a 1:1 vol. mixture thereof. The lanthanum manganese oxide system is highly complex and surprising results with respect to product composition and morphology were obtained. In dependence of the reaction parameters, the La(OH)₃ nanoparticles undergo a shape transformation from short nanorods with an average aspect ratio of 2.1 to micron-sized nanofibers (average aspect ratio is more than 59.5). Although not directly involved, KMnO₄ plays a crucial role in determining the particle morphology of La(OH)₃. The reason lies in the fact that KMnO₄ is able to oxidize the benzyl alcohol to benzoic acid, which presumably induces the anisotropic particle growth in [0 0 1] direction upon preferential coordination to the ±(1 0 0), ±(0 1 0) and ±(−110) crystal facets. By adjusting the molar La(OiPr)₃-to-KMnO₄ ratio as well as by using the appropriate solvent mixture it is possible to tailor the morphology, phase purity and microstructure of the La(OH)₃ nanoparticles. Postsynthetic thermal treatment of the sample containing La(OH)₃ nanofibers and β-MnOOH nanoparticles at the temperature of 800 °C for 8 h yielded polyhedral LaMnO₃ and worm-like La₂O₃ nanoparticles as final products.     

Total synthesis of (+)-epiquinamide

The stereoselective total synthesis of the novel quinolizidine alkaloid (+)-epiquinamide is presented, starting from the amino acid l-allysine ethylene acetal. Key steps in the synthesis involved a highly diastereoselective N-acyliminium ion allylation and a ring-closing metathesis reaction to provide the bicyclic skeleton. [reaction: see text]     

Wechselwirkungen in Kristallen. 106. Mitteilung. Die Klaviatur der Na⊕-Koordinationszahlen in ihren Carbazolanion-Salzen

Interaction in Crystals: The Keyboard of Na⊕ Coordination Numbers in Its Carbazole Anion Salts Some local minima in the shallow potential of the system carbazole anion, sodium cation, and the ethers tetrahydrofuran, 1,2-dimethoxyethane, diglyme, triglyme, tetraglyme, 15-crown-5 as well as 2.2.1-cryptand are explored experimentally and by quantum-chemical calculations. Three prototype contact-ion multiples of Na⊕-solvated carbazole anion M? salts have been crystallized and structurally characterized: polyether-solvated monomers [M?Na⊕_solv]₁, solvent-shared dimers [M?Na⊕_solv]₂, and solvent-separated polyions [(M?)nNa?_solv](^n?1)? [Na⊕_solv](n_?1). The Na⊕ coordination numbers stretch from 3 to 7 as illustrated by the compounds [(M?)₃Na+]??[Na+(2.2.1-crytand)]₂ for 3 and 7, [(M?)₂Na+(THF)₂]? [Na⊕(2.2.1-cryptand)] for 4 and 7, [M? Na+(diglyme)]₂ for 5, or [M? Na+(l 5-crown-5)] for 6. Structural comparison is based on literature analogies as well as on results of MNDO calculations concerning charge distribution and enthalpies of formation. Taken together, the results demonstrate the delicate energy balance, by which cation solvation can influence the formation of organic salts.     

Electron deficiency in tetrahedral transition-metal clusters: electronic structure and magnetic properties of [Ru4(eta6-C6H6)4(mu3-H)4](2+)

Analysis of the electronic structure of the electron-deficient cluster cation [Ru4(eta6-C6H6)4H4](2+) (1(2+)) by density functional theory calculations shows a very small energy gap (0.06 eV) between the diamagnetic singlet state and the paramagnetic triplet state, as a consequence of the absence of a significant Jahn-Teller distortion in the molecular structure of 1(2+). Magnetic measurements of [1]Cl2, [1][BF4]2, and [1][PF6]2 show 1(2+) to be diamagnetic in the fundamental state, with some weak temperature-independent paramagnetism, depending upon the nature of the counterion.