Assessing chiral self-recognition using chiral stationary phases

Chiral stationary phases were synthesized and their ability to separate racemic precursors from which they were derived was assessed. Taken in conjunction with homochiral recognition previously observed in the solid state, the results of this study reveal that a geometrically controlling π-π interaction has a profound influence on molecular recognition.     

Dictyostatin flexibility bridges conformations in solution and in the β-tubulin taxane binding site

Dictyostatin (DCT, 1) is a complex, flexible polyketide macrolide that demonstrates potent microtubule-polymerization activity. Both a solution structure (2a) and a possible binding mode for DCT (Conf-1) have been proposed by earlier NMR experiments. In the present study, the conformational landscape of DCT in DMSO-d(6) and methanol-d(4) was explored using extensive force-field-based conformational searches combined with geometric parameters derived from solution NMR data. The results portray a diversity of conformations for dictyostatin that illustrates the molecule's flexibility and excludes the previously suggested dominant solution conformation 2a. One conformation present in DMSO-d(6) with a 7% population (Conf-2, 0.6 kcal/mol above the global minimum at 298°) also satisfies the TR-NOESY NMR parameters of Canales et al. that characterize the taxane binding-site interaction between DCT and assembled microtubules in water. Application of several docking methods (Glide, Autodock, and RosettaLigand) has identified a low-energy binding model of the DCT/β-tubulin complex (Pose-2/Conf-2) that is gratifyingly compatible with the emerging DCT structure-activity data.     

A general strategy for the stereocontrolled preparation of diverse 8- and 9-membered Laurencia-type bromoethers

A unique procedure to effect a ring-expanding bromoetherification process is described, wherein tetrahydrofurans and tetrahydropyrans are smoothly transformed into 8- and 9-membered bromoethers in a regio- and stereocontrolled manner through the use of BDSB (bromodiethylsulfonium bromopentachloroantimonate). These products resemble the cores of the Laurencia C15 acetogenins. In light of the generality and effectiveness of the approach, this work provides a unique strategy for their laboratory preparation and may implicate a possible biosynthesis pathway.     

TUNKA-133: A new array for the study of ultra-high energy cosmic rays

A new array for studying ultra-high energy cosmic rays was inaugurated in 2009 in the Tunka Valley, about 50 km from Lake Baikal. Having an area of 1 km², the new facility allows us to study cosmic rays with energies of 10¹⁵–10¹⁸ eV via the a unified method for registering Cherenkov radiation from extensive air showers (EASes) and is making a substantial contribution to understanding the origin of ultra-high energy cosmic rays. We describe the current state of the experiment, the new methodological approach, our initial results, and the plans for further development of the array.     

ChemInform Abstract: A Density Functional Theory Study of the Gas‐Phase Hydrolysis of Dinitrogen Pentoxide

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.