New 1,2,3,4-tetrahydropyrrolo[1,2-a]pyrimidinium alkaloids (phloeodictynes) from the New Caledonian shallow-water haplosclerid sponge Oceanapia fistulosa. Structural elucidation from mainly LC-tandem-MS-soft-ionization techniques and discovery of antiplasmodial activity

We report here on new 6-hydroxy-1,2,3,4-tetrahydropyrrolo[1,2-a]pyrimidinium alkaloids, belonging to the phloeodictyne family, isolated from the haplosclerid sponge Oceanapia[=Phloeodictyon]fistulosa(Bowerbank, 1873) from New Caledonian shallow waters. Online LC-ESI-MS analysis, coupled to tandem fragmentation experiments on the crude alkaloid mixture, allowed us to clarify their flat structures, including structural isomers. At least 25 different components, of which 17 are new members with variable terminus and length chains, were characterised, besides less abundant analogues bearing a thioethylguanidine side chain. Crude mixtures and HPLC enriched fractions proved active against chloroquine-resistant Plasmodium falciparum, with IC(50) values ranging from 0.6 to 6 microM, while cytotoxicity against human A-549 cell line was low. This makes these alkaloids a good prospect as leads for novel antimalarial agents.     

Application of phased array techniques to coarse grain components inspection

Ultrasonic inspection of cast stainless steel components from primary and auxiliary cooling circuits of French Nuclear Power Plant has to face with major difficulties due to the coarse grained structure of these materials. Attenuation losses and structural noise are encountered, which limits the performances of defect detection ability, mostly in terms of degraded signal-to-noise ratio and poor sensitivity. To overcome such problems, theoretical and experimental studies have been achieved at the French Atomic Energy Commission, with support from the French Institute for Radiological Protection and Nuclear Safety. Experimental studies have been performed over stainless steel specimen of known coarse structure (equiaxial grains and/or elongated grains), containing artificial reflectors (cylindrical holes and electro-eroded surface breaking notches). Those mock-ups have been inspected using contact probes of different array designs (linear or matrix splitting), and using pulse echo or dual-element techniques. Such arrays allow to control the ultrasonic beam so as to investigate different inspection angles and focusing depths. Experiments were carried out using oblique longitudinal waves, using delay laws computed by a specific model, taking account of acoustical and geometrical properties of the probes and the inspected component. In addition, specific reconstruction techniques have been investigated to enhance the signal-to-noise ratio as well as spatial resolution. These techniques are based on beam-forming summation and multi-angle inspections. Experimental results show that such techniques allow to reduce the speckle noise and to optimise the beam resolution. Those increased performances allow to detect and to size small planar defects located at the inner wall of a thick specimen, using corner and tip diffraction echoes.     

Concentration of sodium ion as the determining factor for the association of dansyl amino acids with the teicoplanin molecule in reversed-phase liquid chromatography

The mechanism of the binding of D,L dansyl amino acids to teicoplanin was investigated. Na+ was used as an indicator of the interactions between the solutes and teicoplanin. The number (n) of sodium ions, Na+, excluded from the solute-teicoplanin interface when analyte transfer occurred was determined. A thermodynamic study and enthalpy-entropy compensation were performed to further explore the interaction mechanism. From these results, it was shown that teicoplanin was balanced between 2 conformational states characterized by distinct enantioselective properties. This approach indicates that liquid chromatography (LC) is a useful tool to extract physicochemical and molecular information from retention data. Thus, LC can be used as a complementary technique with the conventional techniques of molecular interaction analysis.     

New beta-strand macrocyclic peptidomimetic analogues containing alpha-(O-, S- or NH-)aryl substituted glycine residues: synthesis,chemical and enzymatic properties

In so much as bis-macrocyclic peptidomimetics have been recognized as high affinity substrates for HIV-1 protease, we were interested in the design and synthesis of new bis-macrocyclic bioisosteric analogues whose general structure is displayed on Fig. 2. The structures of these new analogues are characterized by the specific replacement of the methylene of the benzyl group directly attached to the N-acyl glycine residue in the original molecule 1, by its main bioisosteres, i.e. O-, S- and NH-aryl groups. Knowing that an intermediate in which an heteroatomic aryl group is directly linked to a free amine glycine residue is not stable, we developed an original synthetic pathway which involved the coupling of a specific side chain to the exocyclic carboxylic acid function, followed by an elegant oxidation-nucleophilic substitution Steglich-type reaction. Analogues 2a-d were then submitted to chemical and enzymatic hydrolysis. We demonstrated that, as expected, the specific cleavage of the exocyclic N-acyl bond led to the release of aryl moieties (phenol, thiophenol and aniline species). These chemical and enzymatic stability studies brought to light the biological potential of such macrocyclic analogues in infected cells.     

Gas-Phase Generation and Photoelectron Spectra of Reactive Unsubstituted Cycloalkenethiones

The flash vacuum thermolysis of cycloalkenyl allyl sulfides, potential precursors of unsubstituted cycloalkenethiones, has been investigated by photoelectron spectroscopy. This technique allowed us to characterize in the gas phase very reactive species of this series, the conjugated and nonconjugated cyclopentene and cyclohexenethiones, and to compare the reactivity of these compounds. The assignment of the PE spectra is supported by electronic structure calculations, particularly by the HF method at the MP2 level and the density functional theory (DFT) using the B3LYP and BP86 functionals with the 6-311G(d, p) basis set. Copyright 2001 Academic Press.     

Connexions conformes sur un fibré vectoriel

We introduce a new formalism to define conformal connections on a vector bundle, endowed with a conformal class of pseudo-riemannian metrics of signature (p, q). Using a bundle map, called isotropic transformation, we show that these non-linear connections are in one-to-one correspondence with metric connections on an enlarged pseudo-riemannian vector bundle, endowed with a metric of signature (p + 1, q + 1). We then use this formalism to give an intrinsic definition of Cartan's conformal circles. Finally, as an example, we give a geometric interpretation of some results of relativistic electromagnetism, connecting to each electromagnetic field a conformal connection on the tangent bundle of the space-time manifold.