Matrix effects in the fast atom bombardment protonation of carbohydrates

FAB positive mass spectra of trehalose in the presence of different matrices such as glycerol, diethanolamine (DEA) and triethanolamine (TEA) are presented and discussed. Protonated and solvated protonated trehalose ions are observed, of which the relative abundance changes with the liquid matrix used. MIKE spectra of the protonated molecular ions solvated by the matrix show unambiguously that desolvation contributes to the formation of protonated molecular ions. It is shown that the decomposition of these complexes is mainly controlled by the relative proton affinities of the analysed sample and the matrix.     

Substitution nucleophile aromatique. Etude cinetique de la C-arylation de cyanoacetamides par les halogenonitrobenzenes dans le N,N-dimethylformamide

The C-arylation of the sodium salt of N,N-dimethylcyanoacetamides, in DMF, has been investigated. The kinetics can be explained if two forms of the nucleophile, the isolated carbanion and the less reactive ion pair, are involved by use of Acree's theory, it has been possible to elucidate constants k_i (for isolated carbanion) and k_p (for ion pair) for different aromatic substrates. The variation of k_i/k_p may account for the selectivity observed in some cases.     

Synthesis of the azaphilones (+)-sclerotiorin and (+)-8-O-methylsclerotiorinamine utilizing (+)-sparteine surrogates in copper-mediated oxidative dearomatization

Enantioselective syntheses of the azaphilone natural products (+)-sclerotiorin and (+)-8-O-methylsclerotiorinamine that possess the natural R-configuration at the quaternary center are reported. The syntheses were accomplished using copper-mediated asymmetric dearomatization employing bis-μ-oxo copper complexes prepared from readily available (+)-sparteine surrogates. Of note, site-selective O-methylation of a vinylogous pyridone was used to access the isoquinolin-6(7H)-one core of (+)-8-O-methylsclerotiorinamine.     

Facile, diversity-orientated one-pot synthesis of ethyl 1,5-disubstituted-1H-1,2,4-triazole-3-carboxylates

Access to the 1,5-disubstituted-1H-1,2,4-triazole-3-carboxamide motif is quite laborious and requires forcing conditions to effect the cyclocondensation step. Herein, we report an efficient and mild one-pot protocol to access this substructure in good chemical yields with high regiocontrol.     

Resonance Paramagnetique Electronique: Reorientation Rotationnelle de Sondes Radicalaires Nitroxydes Dissoutes en Milieu Isotrope. Effect de Solvant

L'ètude par résonance paramagnétique electronique, de la diffusion rotationnelle de sondes radicalaires nitroxydes de géométrie moléculaire de type “sphérique” montre l'influence de la nature protique ou aprotique du solvant sur l'anistropie de réorientation. Cette anisotropie est analysée en fonction de la force de la liaison hydrogène et de la taille des molécules solvatantes. Pour des nitroxydes de forme ellipsoïdale, l'anisotropie de réorientation est liée à la structure moléculaire du radical : pour les molécules étudiées (2-2-6-6-tétramethyl 4-(p-C_n H_2n+1 0-)benzoylamino piperidine 1 oxyl) cette anisotropie ne dépend pratiquement pas de la nature de la chaine alcoyle du radical; d'autre part sa diffusion rotationnelle n'est que tres peu perturbée par la solvatation. Par contre lorsque les sondes précédentes sont dissoutes dans un solvant dont les molécules sont elles-mês fortement anisotropes (octyl benzyl) I'anisotropie de réorientation devient importante; elle est alors voisine de celle observée dans la phase isotrope d'un cristal liquide thermotrope tel que le M.B.B.A.     

On the existence of smooth self‐similar blowup profiles for the wave map equation

Consider the equivariant wave map equation from Minkowski space to a rotationally symmetric manifold N that has an equator (e.g., the sphere). In dimension 3, this paper presents a necessary and sufficient condition on N for the existence of a smooth self‐similar blowup profile. More generally, we study the relation between

• the minimizing properties of the equator map for the Dirichlet energy corresponding to the (elliptic) harmonic map problem and
• the existence of a smooth blowup profile for the (hyperbolic) wave map problem.

This has several applications to questions of regularity and uniqueness for the wave map equation. © 2008 Wiley Periodicals, Inc.