Total synthesis,isolation, surfactant properties,and biological evaluation of ananatosides and related macrodilactone-containing rhamnolipids

Rhamnolipids are a specific class of microbial surfactants, which hold great biotechnological and therapeutic potential. However, their exploitation at the industrial level is hampered because they are mainly produced by the opportunistic pathogen Pseudomonas aeruginosa. The non-human pathogenic bacterium Pantoea ananatis is an alternative producer of rhamnolipid-like metabolites containing glucose instead of rhamnose residues. Herein, we present the isolation, structural characterization, and total synthesis of ananatoside A, a 15-membered macrodilactone-containing glucolipid, and ananatoside B, its open-chain congener, from organic extracts of P. ananatis. Ananatoside A was synthesized through three alternative pathways involving either an intramolecular glycosylation, a chemical macrolactonization or a direct enzymatic transformation from ananatoside B. A series of diasteroisomerically pure (1→2), (1→3), and (1→4)-macrolactonized rhamnolipids were also synthesized through intramolecular glycosylation and their anomeric configurations as well as ring conformations were solved using molecular modeling in tandem with NMR studies. We show that ananatoside B is a more potent surfactant than its macrolide counterpart. We present evidence that macrolactonization of rhamnolipids enhances their cytotoxic and hemolytic potential, pointing towards a mechanism involving the formation of pores into the lipidic cell membrane. Lastly, we demonstrate that ananatoside A and ananatoside B as well as synthetic macrolactonized rhamnolipids can be perceived by the plant immune system, and that this sensing is more pronounced for a macrolide featuring a rhamnose moiety in its native ¹C₄ conformation. Altogether our results suggest that macrolactonization of glycolipids can dramatically interfere with their surfactant properties and biological activity.

We show that macrolactonization of gluco- and rhamnolipids dramatically interfere with their surfactant properties and biological activity.     

A study of ACO capabilities for solving the maximum clique problem

This paper investigates the capabilities of the Ant Colony Optimization (ACO) meta-heuristic for solving the maximum clique problem, the goal of which is to find a largest set of pairwise adjacent vertices in a graph. We propose and compare two different instantiations of a generic ACO algorithm for this problem. Basically, the generic ACO algorithm successively generates maximal cliques through the repeated addition of vertices into partial cliques, and uses “pheromone trails” as a greedy heuristic to choose, at each step, the next vertex to enter the clique. The two instantiations differ in the way pheromone trails are laid and exploited, i.e., on edges or on vertices of the graph. We illustrate the behavior of the two ACO instantiations on a representative benchmark instance and we study the impact of pheromone on the solution process. We consider two measures—the re-sampling and the dispersion ratio—for providing an insight into the performance at run time. We also study the benefit of integrating a local search procedure within the proposed ACO algorithm, and we show that this improves the solution process. Finally, we compare ACO performance with that of three other representative heuristic approaches, showing that the former obtains competitive results.     

Synthesis and polymerization of functionalized dendritic macromonomers

The synthesis of dendritic building blocks (dendrons) of the first generation (G1) and the second generation, which carry differently protected amine groups in the periphery, is reported. The dendrons are used for the synthesis of the corresponding acrylic and methacrylic macromonomers. Their polymerization behavior under radical conditions is investigated. The G1 dendronized polymers are decorated at their peripheral amino groups, that is, with the chiral amino acid L -phenylalanine by the attach-to approach. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1940–1954, 2001     

Über einige Sätze der Gruppentheorie

Ohne Zusammenfassung     

Mirror symmetry formulae for the elliptic genus of complete intersections

In this paper, we calculate the elliptic genus of certain completeintersections in products of projective spaces. We show thatit is equal to the elliptic genus of the Landau–Ginzburgmodels that are, according to Hori and Vafa, mirror partnersof these complete intersections. This provides additional evidenceof the validity of their construction. Received July 6, 2007.     

Internal and Boundary Observability Estimates for the Heterogeneous Maxwell's System

Observability estimates for Maxwell's system with variable coefficients are established using the differential geometry method recently developed for scalar wave equations. The main tool is that Maxwell's system is reducible to a perturbed vectorial wave equation with a decoupled principal part.     

Polymorphic transformation of the Γ-form of d-sorbitol upon milling: structural and nanostructural analyses

In this paper, we study the structural, nanostructural and thermodynamic evolutions of crystalline Γ-sorbitol upon mechanical milling. The investigations have been performed by powder X-ray diffraction and differential scanning calorimetry. The results clearly show that the evolution upon milling can be divided in two stages. The first one only reveals micro and nanostructural modifications of the crystallites appearing through a size reduction, deformations, and changes of shape. On the other hand, the second stage reveals a complete structural transformation of the Γ-form of sorbitol towards the metastable A-form of sorbitol. Special attention has been paid to the nanostructural features derived from the first stage, which trigger the ultimate structural transformation.     

The exact distribution of indefinite quadratic forms in noncentral normal vectors

The exact density of the difference of two linear combinations of independent noncentral chi-square variables is obtained in terms of Whittaker's function and expressed in closed forms. Two distinct representations are required in order to cover all the possible cases. The corresponding expressions for the exact distribution function are also given.     

Complexité dynamique des réseaux de HopfieldDynamical complexity of the Hopfield networks

One considers the Hopfield networks. It is shown that this system can generate any structurally stable inertial dynamics, with a bounded memory. To cite this article: S. Vakulenko, C. R. Acad. Sci. Paris, Ser. I 335 (2002) 639–642.