Acetone promoted 1,4-migration of an alkoxycarbonyl group on a syn-1,2-diamine

A 2-protected cis-amino mitosene undergoes an irreversible acetone promoted isomerization and converts to the 1-isomer. Kinetic studies and DFT calculations of the reaction are reported. An organocatalytic mechanism is proposed, involving a covalent intermediate formed by reaction of the mitosene and acetone.     

Synthesis of fullerodendrons with an ammonium unit at the focal point and their cooperative self-assembly on a fluorescent ditopic crown ether receptor

Dendritic branches with 1, 2, or 4 peripheral fullerene subunits and an ammonium function at the focal point have been prepared. Their ability to form self-assembled dendritic structures with oligophenylenevinylene receptors bearing one or two crown ether moieties has been evidenced by ES-MS studies for the first time. These supramolecular complexes are multicomponent photoactive devices in which the emission of the central receptor is dramatically quenched by the fullerene units. This new property resulting from the association of the different molecular subunits allowed detailed investigations of the self-assembly process by means of fluorescence titrations. The binding studies have revealed positive cooperative effects for the assembly of the fullerodendrimers with the ditopic receptor. Interestingly, the stability of the supramolecular 2:1 structures increases as the size of the dendritic unit increases. This positive dendritic effect has been explained by the larger number of possible intramolecular fullerene-fullerene interactions between the two dendritic guests when the number of fullerene subunits is increased.     

Insensitivity to salt of assembly of a rigid biopolymer aggrecan

Many polyelectrolytes, ranging from sulfonated polystyrene to DNA, exhibit a strong sensitivity of their phase behavior to salt concentration, especially to higher valence salts, which often lead to phase separation. We show that the stiff polyelectrolyte aggrecan exhibits a qualitatively different behavior. Specifically, the scattering properties of aggrecan solutions are exceptionally insensitive to the addition of calcium salt, conferring on aggrecan the role of an ion reservoir mediating calcium metabolism in cartilage and bone, and also providing osmotic resilience to compressive load.     

Solvent effect and librational entropy calculations on N-acetylalanylglycine amide

Entropy and solvent effects are calculated for some conformations of Ala-Gly. The inclusion of these effects in energy calculations show the β_II type structure to be the most stable.     

Greffage de l'acrylonitrile sur le polyethylene et les copolymeres ethylene-propylene peroxydes par voie radiochimique

The radiation-induced peroxidation of polyethylene and ethylene-propylene copolymers was investigated under different irradiation conditions (temperature, dose and dose-rate). The buildup of peroxides was derived from the kinetics of the graft copolymerization of acrylonitrile on the irradiated polymers. The results show that the mechanism of peroxidation of polyethylene depends on irradiation temperature. A chain hydroperoxidation is observed at a certain temperature, largely above T_g of the polymer, whereas a single step peroxidation leading to a mixture of biperoxides and hydroperoxides occurs at lower temperatures. The critical temperature above which chain hydroperoxidation sets in increases the higher the dose-rate. For the poly(ethylene-co-propylene), special precautions were taken to remove the anti-oxidant of the polymer. A chain hydroperoxidation process was observed at all temperatures above T_g. These various results are discussed.     

4-Hydroxy-6-methoxyaurones with high-affinity binding to cytosolic domain of P-glycoprotein

A series of 4-hydroxy-6-methoxyaurones and 4,6-dimethoxyaurones has been synthesised and tested for their binding affinity toward the nucleotide-binding domain of P-glycoprotein, an ABC (ATP-Binding Cassette) transporter which mediates the resistance of cancer cells to chemotherapy. These compounds differ from each other by the nature of the substituent on the aurone B-ring. The binding affinity seems to be linked to the nature of the substituent, as well as to the presence or the absence of a hydroxy group at position 4. The most active compounds were 4'-bromo-4-hydroxy-6-methoxyaurone and 4-hydroxy-4'-iodo-6-methoxyaurone.     

Synthése totale d'α-disaccharidyles de tridésoxy-2,5,6-streptamine apparentés aux aminosides à partir du maltose et du lactose

Total synthesis of α-disaccharidyl-2,5,6-trideoxy-streptamines related to aminoglycoside antibiotics derived from maltose and lactose The synthesis of the hitherto unknown 4-O-substituted α-linked pseudo-tri-saccharides 1,2 and 3 is described. The key intermediates required in the reaction sequence are the glycals 12, 13 and 14 , prepared from maltose, lactose and the chiral ditosyloxy-cyclohexanol 15 , readily accessible from quinic acid. The pivotal step in the reaction's scheme - a stereospecific α-glycosylution procedure -, is an acid-catalyzed addition of the alcohol 15 to the glycals 12, 13 and 14 leading to the corresponding 2,3-unsaturated trisaccharides. The latter compounds were transformed to the target α-glycosides of 2,5,6-trideoxystreptamine 1, 2 and 3 which were devoid of significant antibacterial activity. These results indicate that the presence of an ether linkage at the position 4′ is probably critical for antibacterial activity.     

Nanometric sponges made of water-soluble hydrophobic dendrimers

The behavior of a fifth generation phosphorus dendrimer having a hydrophobic interior and hydrophilic end groups is studied in solution in water using the pulsed-field gradient spin-echo NMR technique. Addition of THF to this solution induces dramatic changes concerning the size of the dendrimer (+150% in volume), T1 relaxation of THF, and viscosity. This dendrimer behaves like a highly singular nanotool, able both to modify its environment and to be modified by it.