Chemistry of vinyl sulfones. Approach to novel conformationally restricted analogues of glutamic acid

A totally different approach to conformationally restricted glutamic acid analogues is described, in which one of the acid functions is replaced by a cyclopropanol. The reactivity of cyclopropanol vinyl sulfones toward addition of lithiated Schöllkopf bislactim ether provides a facile synthesis of α-amino acid diastereoisomers. Conformational analysis of these analogues, incorporating solvation effects, and docking to a glutamate receptor model, are used to show the relevance of the conformational restrictions employed.     

The reactions of methyl radicals with chloromethanes

The reaction of methyl radicals with CCl₄ and CCl₃Br have been reinvestigated in the gas phase over a wide range of temperatures and pressures using both the photolysis of acetone and the pyrolysis of di-tertiary butyl peroxide (dtBP) as the methyl radical sources. The results are in essential agreement with previous work; however, these new studies provide evidence that at higher pressures the major source of HCl in the reactions is due to methyl radical attack on CH₃CCl₃, formed via the combination of methyl and trichloromethyl radicals. From these investigations Arrhenius parameters for the reactions have been determined: Pyrolysis of dtBP in the presence of relatively high-pressure mixtures of CCl₄ and CCl₃Br resulted in no enhanced methane formation, since, under these conditions, the only termination product is C₂Cl₆, and the HCl precursor CH₃CCl₃ is not formed. A competitive technique has been used in which dtBP was pyrolysed in the gas phase in the presence of high-pressure mixtures of CCl₃Br and a chloromethane. Arrhenius parameters were obtained for the reactions and the results were used to provide information on the importance of polar effects for hydrogen abstraction from halogenated methanes.     

Synthesis and purification of the allofarnesenes

The eight isomers of allofarnesene (3,7,11-trimethyl-2,4,6,10-dodecatetraene) were prepared using Wittig reactions. The four E-4 isomers could be separated using GC but the unstable Z-A isomers required HPLC on silver nitrate impregnated silica gel for analysis. Purified samples of each isomer were prepared for spectral studies. The configuration of the pseudoionone (6,10-dimethyl-3,5,9-undecatriene-2-one) starting materials was also studied, confirming previous results.     

1,2,3,4-tetrasubstituted isoquinoline acetic acids

Differentially tetrasubstituted isoquinolines are now conveniently prepared by rearrangement of the readily obtainable indanones.     

Taylor dispersion in systems of sedimenting nonspherical Brownian particles : II. Homogeneous ellipsoidal particles

An Aris-type moment scheme is applied to calculate the Taylor-Aris dispersion tensor for the sedimentation of small homogeneous ellipsoidal (and other orthotropic) particles settling under the influence of gravity in a quiescent viscous fluid and undergoing rotational and translational Brownian motions. This generalizes to triaxial particles a prior dispersion result for centrally symmetric bodies of revolution, such as spheroids. An independent Langevin-type dispersivity calculation is shown to yield results identical to those obtained by the moment scheme. The components and of the transversely isotropic dispersion dyadic, parallel and perpendicular, respectively, to the direction of the gravitational field, are shown to be given by the Taylor—Aris-type formulasHere, is the mean settling velocity of the particle, and and

Full-size image

and (d₁,d₂,d₃) respectively the appropriate diffusivity components along the principal axes of the particle. The dimensionless coefficient γ, which is of order unity, is given by the formulaThis anisometric parameter vanishes identically for spherical particles and other hydrodynamically isotropic particles (e.g., cubes, tetrahedra, octahedra, etc.) whose translational and rotational hydrodynamic resistances are independent of the orientation of the particle relative to the directions of its linear and angular velocity vectors. Upon utilizing the translational and rotational Stokes-Einstein equations, explicit numerical values of and are furnished for ellipsoids of revolution of various aspect ratios and sizes when settling in water. Physical restrictions pertaining to sedimentation-vessel apparatus size and the requirement of reasonable sedimentation times greatly restrict the range of particle sizes whose anisometric properties may be experimentally investigated by this new particle-shape characterization technique.