Synthesis and reactivity of furoquinolines bearing an external methylene-bond: access to reduced and spirocyclic structures

A family of furoquinolines were efficiently obtained through a tandem acetalization/cycloisomerization process catalyzed by (5 mol%) silver imidazolate polymer and triphenylphosphine, and diversity was brought by the use of 7 different alcohol groups. From these furoquinolines, 3 examples of reduced derivatives could be obtained (d.r. up to 94 : 6), 10 different spiroketal derivatives by hetero-Diels-Alder reaction (d.r. up to 20 : 1), 8 hetero-[5,5]-spirocycles by cycloaddition with dibromoformaldoxime (d.r. up to 86 : 14) and finally 6 hetero-[5,6]-spirocycles by [4 + 2] cycloaddition with ethyl 3-bromo-2-(hydroxyimino)propanoate (d.r. up to 90 : 10).     

Total synthesis of pinnatoxins A and G and revision of the mode of action of pinnatoxin A

Pinnatoxins belong to an emerging class of potent marine toxins of the cyclic imine group. Detailed studies of their biological effects have been impeded by unavailability of the complex natural product from natural sources. This work describes the development of a robust, scalable synthetic sequence relying on a convergent strategy that delivered a sufficient amount of the toxin for detailed biological studies and its commercialization for use by other research groups and regulatory agencies. A central transformation in the synthesis is the highly diastereoselective Ireland-Claisen rearrangement of a complex α,α-disubstituted allylic ester based on a unique mode for stereoselective enolization through a chirality match between the substrate and the lithium amide base. With synthetic pinnatoxin A, a detailed study has been performed that provides conclusive evidence for its mode of action as a potent inhibitor of nicotinic acetylcholine receptors selective for the human neuronal α7 subtype. The comprehensive electrophysiological, biochemical, and computational studies support the view that the spiroimine subunit of pinnatoxins is critical for blocking nicotinic acetylcholine receptor subtypes, as evidenced by analyzing the effect of a synthetic analogue of pinnatoxin A containing an open form of the imine ring. Our studies have paved the way for the production of certified standards to be used for mass-spectrometric determination of these toxins in marine matrices and for the development of tests to detect these toxins in contaminated shellfish.     

A Note on Degree Conditions for Traceability in Locally Claw-Free Graphs

We say that a set S of vertices is traceable in a graph G whenever there is a path in G containing all vertices of S. In this paper we study the problem of traceability of a prescribed set of vertices in a locally claw-free graph (i.e. a graph in which some specified vertices are not centers of an induced claw). In particular we give sufficient degree conditions restricted to the given set S of vertices for the traceability of S.     

Effect of the experimental parameters on the number of free electrons in the drift region of a wire-cylinder electrostatic precipitator

The aim of this paper is to highlight the number evolution of free electrons in the drift region of a wire-cylinder electrostatic precipitator in negative voltage depends on the experimental parameters, more particularly of gas composition. A numerical model of the negative DC corona discharge developed by Chen et al. was used and modified to investigate the negative discharge corona for different gases. A parametric study was conducted to examine the effect on the electron distribution of operating conditions. The results showed the electron concentration increases with temperature, decreases when the pressure increases, and is closely related to gas composition.     

Comparison of In Vivo Optical Systems for Bioluminescence and Fluorescence Imaging

In vivo optical imaging has become a popular tool in animal laboratories. Currently, many in vivo optical imaging systems are available on the market, which often makes it difficult for research groups to decide which system fits their needs best. In this work we compared different commercially available systems, which can measure both bioluminescent and fluorescent light. The systems were tested for their bioluminescent and fluorescent sensitivity both in vitro and in vivo. The IVIS Lumina II was found to be most sensitive for bioluminescence imaging, with the Photon Imager a close second. Contrary, the Kodak system was, in vitro, the most sensitive system for fluorescence imaging. In vivo, the fluorescence sensitivity of the systems was similar. Finally, we examined the added value of spectral unmixing algorithms for in vivo optical imaging and demonstrated that spectral unmixing resulted in at least a doubling of the in vivo sensitivity. Additionally, spectral unmixing also enabled separate imaging of dyes with overlapping spectra which were, without spectral unmixing, not distinguishable.     

Ultrasonic cavitation applied to the treatment of bisphenol A. Effect of sonochemical parameters and analysis of BPA by-products

Bisphenol A (BPA), a chemical compound largely used in the plastics industry, can end up in aquatic systems, which it disturbs by its endocrine disrupting effect (EDE). This study investigated the BPA degradation upon ultrasonic action under different experimental conditions. The effect of saturating gas (oxygen, argon and air), BPA concentration (0.15-460 micromol L(-1)), ultrasonic frequency (300-800 kHz) and power (20-80 W) were evaluated. For a 118 micromol L(-1)-BPA solution, with the best performance obtained at 300 kHz, 80 W, with oxygen as saturating gas. In these conditions, BPA can be readily eliminated by the ultrasound process (approximately 90 min). However, even after long ultrasound irradiation times (9 h), more than 50% of chemical oxygen demand (COD) and 80% of total organic carbon (TOC) remained in the solution. Analyses of intermediates using HPLC-MS investigation identified several products: monohydroxylated bisphenol A, 4-isopropenylphenol, quinone of monohydroxylated bisphenol A, dihydroxylated bisphenol A, quinone of dihydroxylated bisphenol A, monohydroxylated-4-isopropenylphenol and 4-hydroxyacetophenone. The presence of these hydroxylated aromatic structures showed that the main ultrasonic BPA degradation pathway is related to the reaction of BPA with the *OH radical. After 2h, these early products were converted into biodegradable aliphatic acids.     

The successive reduction of data subsets: A new method for estimating parameters of thermodynamic models

The successive reduction method allows the fitting of models to large sets of data using microcomputers of moderate memory size. It relies on the assumption that the information brought by a set of data is summarized by the maximum likelihood parameters and their inverse variance—covariance matrix. The parameters are estimated from the last data subset, taking account of the information brought by the former ones. The successive reduction method is compared with the classical 'global' method. They give exactly the same results for linear models. With a non-linear model, equivalent results are obtained when this model is consistent with the data. Applications are presented, relating to parameter estimation for generalized equations of state, to vapour—liquid equilibrium and excess enthalpy data reduction using the NRTL and UNIQUAC models.     

Hybrid Systems and Hybrid Computation 1st Part: Hybrid Systems

In the first part of this paper we will give a short historical survey of the field of hybrid systems, a precise definition of a hybrid system and some comments on the definition. In a second paper (Hybrid systems and hybrid computation – 2nd part: Hybrid computation) we will concentrate on a particular aspect of the theory closely related to scientific computation, that we have called hybrid computation.     

Cytotoxic triterpenoid saponins from the roots of Cephalaria gigantea

Three new oleanane-type saponins, giganteosides L (1), M (2) and N (3) along with eight known ones were isolated from the roots of Cephalaria gigantea. Their structures were established as 3-O-[beta-D-galactopyranosyl-(1-->2)-beta-D-glucuronopyranosyl]-28-O-[beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranosyl]-oleanolic acid, 3-O-[beta-D-galactopyranosyl-(1-->2)-beta-D-glucuronopyranosyl]-28-O-[beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranosyl]-hederagenin, 3-O-[alpha-L-rhamnopyranosyl-(1-->2)-beta-D-glucuronopyranosyl]-28-O-[beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranosyl]-hederagenin, respectively, by means of spectroscopic methods (1D and 2D NMR, HR-ESI-MS). Cytotoxic activity of monodesmosides was investigated in vitro using three cancer cell lines, namely, human non pigmented melanoma MEL-5 and human leukemia HL-60. Giganteosides D (4) and E (5) showed antiproliferative effect on human cell lines with IC(50) values in the range 3.15-7.5 microM.