A recyclable chiral Ru catalyst for enantioselective olefin metathesis. Efficient catalytic asymmetric ring-opening/cross metathesis in air

The synthesis and structure of a new chiral bidentate imidazolinylidene ligand and a derived chiral Ru-based carbene are disclosed. The Ru complex is stereogenic at the metal center; it can be prepared in >98% diastereoselectivity and purified by silica gel chromatography with undistilled solvents. The air-stable Ru complex efficiently catalyzes ring-closing and ring-opening metathesis and is recyclable. The chiral complex is highly effective (0.5-10 mol % loading) in promoting enantioselective ring-opening/cross metathesis reactions (up to >98% ee). These enantioselective transformations can be effected in air, with unpurified solvent and with substrates that would only polymerize with Mo-based catalysts.     

Spins of the levels and multipole mixing ratios of transitions in 125Sb determined from γ-γ directional correlation and polarization-directional correlation measurements

In order to resolve several discrepancies in spin assignments to levels in ¹²⁵Sb, directional correlations and polarization-directional correlations have been measured for several γ-γ cascades in ¹²⁵Sb populated from the decay of ¹²⁵Sn. Earlier results obtained from using NaI and Ge(Li) and NaI detectors were difficult to interpret due to the complex structure of the decay scheme. To improve the experimental situation, we have used two coaxial Ge(Li) detectors for the angular correlation measurements and a coaxial Ge(Li)-planar Ge(Li) combination for the polarization-directional correlations. Combination of the results of these measurements give unique spin assignments of $\text{11}\text{2}$^?, $\text{11}\text{2}$^?, $\text{9}\text{2}$⁺, $\text{11}\text{2}$⁺ and $\text{9}\text{2}$⁺ to the 1982 keV, 1890 keV, 1420 keV, 1089 keV and 1067 keV levels, respectively. The determined E2/M1 mixing ratios are : δ(470) = 0.010±0.027, δ(1067) = ?0.86±0.18, and δ(916) = ?0.02±0.01.     

Chiral Ru-based complexes for asymmetric olefin metathesis: enhancement of catalyst activity through steric and electronic modifications

Design, synthesis, characterization, and catalytic activity of six enantiomerically pure Ru-based metathesis catalysts are disclosed (3a-3f). The new chiral catalysts were prepared through steric and electronic alterations of the parent catalyst system (3). The present studies indicate that the effect of structural modifications of chiral complex 3 does not always correspond to those of the related achiral complexes. The present findings illustrate that modified Ru complexes (3e and 3f) deliver reactivity levels that are more than 2 orders of magnitude higher than 3. Reactivity and physical data are provided that shed light on the origin of activity differences. Some members of the new generation of chiral Ru catalysts promote asymmetric ring-opening (AROM) and ring-closing (ARCM) metatheses that cannot be effected by the first generation chiral catalyst (3).     

Energy expenditure in cyclo-loading processes

A theoretical analysis of the energy expenditure in cyclo-loading vs. quasi-static processes is presented. The analysis refers to processes of a tool-soil interaction, such as implement penetration, cutting, crushing, shovelling etc. The analysis reaches a conclusion stating that no unilateral preference statement can be drawn, thus justifying the experimental results available. It is shown that the existence of an optimal cyclo-loading regime, challenging the quasi-static regime, strongly depends on the character of the loading-unloading curves defining the tool-soil system under consideration. A simple criterion providing an immediate answer to the question of the cyclic vs. quasi-static process preference is derived. The energy expenditure per unit displacement function is thoroughly investigated.     

Quality by design (QbD) based development of a stability indicating HPLC method for drug and impurities

In this paper, an application of Quality by Design (QbD) concepts to the development of a stability indicating HPLC method for a complex pain management drug product containing drug substance, two preservatives, and their degradants is described. The QbD approach consisted of (i) developing a full understanding of the intended purpose, (ii) developing predictive solutions, (iii) designing a meaningful system suitability solution that helps to identify failure modes, and (iv) following design of experiments (DOE) approach. The starting method lacked any resolution among drug degradant and preservative oxidative degradant peaks, and peaks for preservative and another drug degradant. The method optimization was accomplished using Fusion AE? software (S-Matrix Corporation, Eureka, CA) that follows a DOE approach. Column temperature (50 ± 5°C), mobile phase buffer pH (2.9 ± 0.2), initial % acetonitrile (ACN, 2 ± 1%), and initial hold time (2.5, 5, or 10 min) of the HPLC method were simultaneously studied to optimize separation of the unresolved peaks. The optimized HPLC conditions (column temperature of 50°C, buffer pH of 3.1, 3% initial ACN with 2.5 min initial hold) resulted in fully resolved peaks in the two critical pairs. The QbD based method development helped in generating a design space and operating space with knowledge of all method performance characteristics and limitations and successful method robustness within the operating space.     

Glycomimetic building blocks: a divergent synthesis of epimers of shikimic acid

A divergent synthesis of (-)-4-epi-shikimic acid was developed. This route features a one-pot zinc-mediated reductive ring opening of an arabinofuranose followed by a Barbier reaction and culminates in a ring-closing metathesis. Functionalization of (-)-4-epi-shikimic acid via conjugate addition of a thiol occurs in high diastereoselectivity to afford a product with the features of fucosylated glycans.     

On a Helly-type question for central symmetry

Periodica Mathematica Hungarica - We study a certain Helly-type question by Konrad Swanepoel. Assume that X is a set of points such that every k-subset of X is in centrally symmetric convex...     

On the structure of symmetry generators

In a field theoretic framework we investigate generators of symmetry transformations induced by conserved local, not necessarily translationally covariant currents. Assuming the invariance of the vacuum and a mass gap, it is shown that the generator on one-particle states in general can be any polynomial of the generators of the Poincaré group and the internal symmetries. We give an example showing that the generator, defined as an integral over a conserved current, in spite of leaving the vacuum invariant, need not be self-adjoint.Supported by a DAAD grant