Toward the synthesis of spirastrellolide a: construction of a tetracyclic C26-C40 subunit containing the DEF-bis-spiroacetal

[reaction: see text] A stereo-controlled synthesis of the fully elaborated C26-C40 tricyclic [5,6,6]-bis-spiroacetal of spirastrellolide A containing the C28 chlorine substituent is reported, exploiting asymmetric Sharpless dihydroxylation and boron-mediated allylation methodology.     

Inhibition studies on salicylate synthase

Analogues of chorismate and isochorismate were designed and tested as potential inhibitors in the first inhibition study against a salicylate synthase.     

Parameter fitting for piano sound synthesis by physical modeling

A difficult issue in the synthesis of piano tones by physical models is to choose the values of the parameters governing the hammer-string model. In fact, these parameters are hard to estimate from static measurements, causing the synthesis sounds to be unrealistic. An original approach that estimates the parameters of a piano model, from the measurement of the string vibration, by minimizing a perceptual criterion is proposed. The minimization process that was used is a combination of a gradient method and a simulated annealing algorithm, in order to avoid convergence problems in case of multiple local minima. The criterion, based on the tristimulus concept, takes into account the spectral energy density in three bands, each allowing particular parameters to be estimated. The optimization process has been run on signals measured on an experimental setup. The parameters thus estimated provided a better sound quality than the one obtained using a global energetic criterion. Both the sound's attack and its brightness were better preserved. This quality gain was obtained for parameter values very close to the initial ones, showing that only slight deviations are necessary to make synthetic sounds closer to the real ones.     

Nonperturbative renormalization-group study of reaction-diffusion processes

We generalize nonperturbative renormalization group methods to nonequilibrium critical phenomena. Within this formalism, reaction-diffusion processes are described by a scale-dependent effective action, the flow of which is derived. We investigate branching and annihilating random walks with an odd number of offspring. Along with recovering their universal physics (described by the directed percolation universality class), we determine their phase diagrams and predict that a transition occurs even in three dimensions, contrarily to what perturbation theory suggests.     

Synthesis of ether oligomers

[structure: see text] Hydroxyaromatic aldehydes and ketones were used as building blocks to prepare ether oligomers. An iterative two-step protocol involving Mitsunobu coupling and carbonyl reduction provided a protecting-group-free route with high yields. Activity screening of an 84-member library against proteases led to the discovery of micromolar inhibitors for trypsin, chymotrypsin, and subtilisin.     

Modified z-gradient filtering as a mean to obtain phased deuterium autocorrelation 2D NMR spectra in oriented solvents

We describe a modified z-gradient filter scheme specifically designed to obtain pure absorption mode deuterium 2D NMR spectra recorded in oriented solvents. The proposed technique is investigated by analysing the evolution of the density operator for a spin I=1. The method is applied to the recently designed Q-COSY and Q-resolved 2D experiments to simplify the analysis of chiral molecules dissolved in weakly orienting chiral liquid crystals. The efficiency of this z-gradient filtering technique is illustrated using the perdeuterated 1-butanol, a prochiral molecule of average Cs symmetry, dissolved in an organic solution of poly-gamma-benzyl-L-glutamate (PBLG). The experimental results as well as the advantages of the new experiments compared with the previous ones are described and discussed.