Chemical modification of acetylcholinesterase with methoxypolyethylene glycol

Acetylcholinesterase (AChE) (EC 3.1.1.7) was modified with activated monomethoxypolyethylene glycol (mPEG). A decrease of 50% in the catalytic activity was measured during the coupling reaction and the change in the surface properties of AChE was used to separate by hydrophobic interaction chromatography the native and the modified enzyme. The native and the modified enzymes were found to have the same optimalcatalytic conditions. Moreover, the Michaelis constant of both enzymes were similar, whereas theV _m and the bimolecular-velocity constant calculated for organophosphorus inhibitors were slightly higher for the modified AChE. Finally, the modification with mPEG did not improve the thermal stability, whereas the stability in a few organic solvents increased.     

A Direct Asymmetric Synthesis of Juglomycin A

Juglomycin A has been synthesized in four steps from 5-methoxy-1-naphthol.     

Nucléosides de synthése XXII: Obtention,comme synthons oligoxylonucléotidiques,de d-xylofurannosyl adenines spécifiquement substitués

This work describes the synthesis of certain nucleoside synthons which are necessary in order to obtain oligoxylonucleotides. The utilization of a non-symmetrically substituted xyloside substituted at the 2-position permits one to obtain, in satisfactory yields, the described nucleoside which is conveniently protected. All of the compounds described have been fully characterized using the usual analytical methods.     

Phytochemicals from Echinacea and Hypericum: A Direct Synthesis of Isoligularone

Reaction of trienes with α,β-unsaturated aldehydes produces bicyclic products via a tandem Diels-Alder/ene reaction. The adduct from tiglic aldehyde was converted into isoligularone by conversion to a furan followed by benzylic oxidation.     

Polarisabilites moléculaires et effet diélectrique de milieu à l'état liquide. Étude théorique de la molécule d'eau et de ses diméres

The model of Onsager in which a polar molecule undergoes a reaction field due to the polarization of the molecular surroundings is used to evaluate by a S.C.F. calculation (CNDO/2 approximation) the modifications of a molecular structure in the liquid state.Application to water molecule and to three polar dimers for values of the dielectric constant varying between 3 and 78, shows that most of geometric parameters and dipoles moments vary of few per cent when the molecule is inserted in a liquid. In the liquid state dipole moments do not depend very much on the dielectric constant but energies and relative stabilities of isomers are strongly dependent on the medium.[/p]

     

A self-consistent reaction field model of solvation using distributed multipoles. I. Energy and energy derivatives

The self-consistent reaction field model developed previously by the authors in the case of single center multipole expansion of the electronic structure of the solute has been extended to the case of a distributed multipole expansion. Three different expansions have been tested and two of them have proved to be rapidly convergent. The performances of the code are illustrated by the density functional theory treatment of few test systems: guanine, cytosine, and cytosine hydrated with one and three water molecules. A robust fast computer code has been tested to get the electronic structure, the electrostatic contribution to the solute-solvent free energy of interaction, and the optimized molecular geometry in solution.     

Diels-Alder reactions of quinol lactones: a change of regioselectivity with stannic chloride catalysis

Lewis acid-mediated Diels-Alder reactions of quinol lactone 2 gave regioselectivity opposite to that of the uncatalyzed reaction. Compound 12 is proposed as the reactive intermediate generated by the reaction of 2 with stannic chloride.     

Vanillic acid 4-O-beta-D-(6'-O-galloyl) glucopyranoside and other constituents from the bark of Terminalia macroptera Guill.et Perr

A new phenolic glucoside gallate, vanillic acid 4-O-beta-D-(6'-O-galloyl) glucopyranoside (1) was isolated from the bark of Terminalia macroptera Guill.et Perr., together with 3,3',4'-tri-O-methylellagic acid (2) and two triterpene glucopyranosyl esters, 24-deoxysericoside (3) and chebuloside II (4). Compounds 2-4, not described previously for this plant, showed antimicrobial activities against Bacillus subtilis, while 3 and 4 possessed haemolytic properties. In both assays 1 was found to be inactive.     

Efficient and Highly Selective Oxidation of Primary Alcohols to Aldehydes by N-Chlorosuccinimide Mediated by Oxoammonium Salts

2,2,6,6-Tetramethyl-1-piperidinyloxy catalyzes efficient oxidation of primary alcohols to aldehydes by N-chlorosuccinimide, in a biphasic dichloromethane-aqueous pH 8.6 buffer system in the presence of tetrabutylammonium chloride. Aliphatic, benzylic, and allylic alcohols are readily oxidized with no overoxidation to carboxylic acids. Secondary alcohols are oxidized to ketones with a much lower efficiency. Very high chemoselectivities are observed when primary alcohols are oxidized in the presence of secondary ones. Primary-secondary diols are selectively transformed into hydroxy aldehydes, with, in some cases, no detectable formation of the isomeric keto alcohols.