Halo-enediynes: probing the electronic and stereoelectronic contributions to the Bergman cycloaromatization

A series of halogen-substituted cyclic enediynes were prepared with use of carbenoid coupling strategy. DFT analysis, initially used to identify synthesis candidates, was also employed to rationalize the propensity for cycloaromatization of the compounds. In all cases studied the halogen atom had a strongly retardative effect on the thermal Bergman cycloaromatization reaction. The isolation of the first C-9 monochloroenediyne is noteworthy, and may find application in prodrug design.     

Synthesis of 2-Acetoxy-2-Methoxy-4-Acetoxymethyl-3,5-Cyclohexadien-1-One by Lead Tetraacetate Oxidation of Homovanillic Acid

An efficient synthesis of the title compound is achieved when homovanillic acid is reacted with lead tetraacetate.     

Synthesis and protein degradation capacity of photoactivated enediynes

[structure: see text] The viability of proteins as targets of thermally and photoactivated enediynes has been confirmed at the molecular level. Model studies using a labeled substrate confirmed the efficacy of atom transfer from diyl radicals produced from enediynes to form captodatively stabilized carbon centered aminoacyl radicals, which then undergo either fragmentation or dimerization. To exploit this finding, a family of enediynes was developed using an intramolecular coupling strategy. Derivatives were prepared and used to target specific proteins, showing good correlation between affinity and photoinduced protein degrading activity. The findings have potential applications in the design of artificial chemical proteases and add to our understanding of the mechanism of action of the clinically important enediyne antitumor antibiotics.     

Diastereoselective spiroannulation of phenolic substrates: synthesis of (+/-)-2-tert-butyl-6-methoxy-1-oxaspiro[4,5]deca-6,9-diene-8-one

The synthesis of a new spiroether is described. The title compound is obtained as a diastereomeric mixture in 45% yield.     

Space correlation measurements in a forced shear layer with wall injection

Comprehension of wall-injection flow in a channel in the presence of different geometric discontinuities is necessary as part of the general investigations concerning combustion instabilities of solid propellant rocket motors. In order to characterise the aerodynamic flow field and to evaluate the influence of an obstacle inside a porous channel in such a case, experimental studies were conducted on a 1/40 scale model of the new ARIANE V motor. In fact, the flow is only induced by wall-injection and the presence of an obstacle creates a particular shear layer development in the obstacle wake. Particular attention was given to the unstable dynamic conditions of the shear layer. A thermal seeding of the shear layer was made in order to qualify the heat transfer therein, and especially to emphasise the turbulent structure development. Transverse and longitudinal spatial correlations were measured to characterise turbulence scales in the shear layer. At the origin of the shear layer, the decay of turbulence memory is found to be similar to that observed in a forced flow boundary layer, but the injecting wall modifies the change in structures. The wall flow is found to preserve the turbulent structures in such a way that the turbulence memory predominates in a longitudinal direction.List of Symbols f frequency (Hz) - h channel height (m) - h _v obstacle height (m) - L mean dimension of large structures (m) - P pressure (Pa) - m mass flow rate (kg/s) - r distance between probes in X direction (m) - r ^+(–) distance between probes in Y direction (m) - u longitudinal velocity in X direction (m/s) - v transversal velocity in Y direction (m/s) - T temperature (K) - x,y,z axis system (m) - t = T-T _amb (K) - v kinematic viscosity (mVs) - density (kg/m³) - characteristic porous size (urn) - _u longitudinal rms (m/s) - I _u dynamic turbulence intensity _u /u _max - I _T thermal turbulence intensity - M Mach number u/a - Re _w wall Reynolds number v _w h/v - Re _c longitudinal Reynolds number u _c h/v - R _uT thermal dynamic correlation coefficient - St Strouhal number fh/u - X,Y,Z axis system normalised by the channel height h - X _S longitudinal position of the obstacle - X X-X _S - amb ambient reference - c flowing cavity - fav head end - l lateral direction - g longitudinal direction max maximum at a longitudinal position - w wall The authors thank the CNES for its financial support, and in particular E. Robert and R. Bee.     

Analysis of self-sustained oscillation sources in segmented flows

The analysis of self-sustained oscillations in segmented flow generated through porous walls has been carried out over a wide range of velocity levels; in fact, we studied a cold gas flow induced by injection through different wall injecting blocks. We have attempted in this study to analyse the potential unstable development occurring in solid propellant rocket motors. We lay emphasis upon the phenomenon of wall vortex shedding insofar as it conduces to acoustic mode resonance in the whole chamber, within whose confines impingement of such structures generates a source of noise. It is on account of segmented flow that the thin shear layer develops and that the aforementioned vortex shedding comes to induce aero-acoustic coupling. Subsequent experimental results highlight a link in such flows between these two noise sources - they also allow one to observe a pronounced form of selectivity in the energy transfer, i.e. in longitudinal acoustic mode amplification, which has an attested effect upon all of the pressure oscillations in the chamber.     

Energy dependence of multiplicity in proton-nucleus collisions and models of multiparticle production

This is a continuation of our earlier investigation (Gurtuet al 1974Phys. Lett. 50 B 391) on multiparticle production in proton-nucleus collisions based on an exposure of emulsion stack to 200 GeV/c beam at the NAL. It is found that the ratioR _em = 〈n _s〉/〈n _ch〉, where 〈n _ch〉 is the charged particle multiplicity in pp-collisions, increases slowly from about 1 at 10 GeV/c to 1·6 at 68 GeV/c and attains a constant value of 1·71 ± 0·04 in the region 200 to 8000 GeV/c. Furthermore,R _em = 1·71 implies an effectiveA-dependence ofR _A =A ^0.18,i.e., a very weak dependence. Predictions ofR _em on various models are discussed and compared with the emulsion data. Data seem to favour models of hadron-nucleon collisions in which production of particles takes place through adouble step mechanism,e.g., diffractive excitation, hydrodynamical and energy flux cascade as opposed to models which envisage instantaneous production.