A new saponin lactone from Astragalus corniculatus

A new oleanane-type saponin lactone was isolated from the ethanolic extract of the aerial parts of Astragalus corniculatus Bieb. The structure of the saponin was elucidated as 19-hydroxyolean-12-ene-28, 21beta-olide 3beta-D-xylopyranoside (1) by chemical and spectral methods.     

A prediction problem in

For a nonnegative integrable weight function on the unit circle , we provide an expression for , in terms of the series coefficients of the outer function of , for the weighted distance , where is the normalized Lebesgue measure and ranges over trigonometric polynomials with frequencies in , , . The problem is open for .

     

BDH-TTP as a Structural Isomer of BEDT-TTF,and Its Two-Dimensional Hexafluorophosphate Salt

Metallic behavior down to low temperature is shown by charge transfer salts of BDH-TTP ( 1 ), a structural isomer of bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF). In the case of (BDH-TTP)₂PF₆ this behavior is attributed to the structure, which is made up of κ-type sheets of BDH-TTP donor molecules and sheets of PF₆⁻ anions.     

Analysis of the high-resolution infrared spectrum of cyclopropane

The high-resolution infrared spectrum of cyclopropane (C₃H₆) has been measured from 100 cm⁻¹ to 2200 cm⁻¹. In that region we have identified 24 absorption bands attributed to six fundamental bands, five combination bands, three hot bands and 10 difference bands. Long pathlength spectra, up to 32 m, facilitated the identification and analysis of many previously unstudied infrared inactive, and Raman and infrared inactive vibrational states, including direct access to two forbidden fundamental states, ν₄ and ν₁₄. An improved set of constants for the ground vibrational state as well as for the fundamental vibrations ν₇, ν₉, ν₁₀, ν₁₁ are also reported. The spectral resolution of the measurements varied from 0.002 cm⁻¹ to 0.004 cm⁻¹.     

Synthesis and properties of PI polyamide-SAHA conjugate

We have designed and synthesized new types of pyrrole (P)-imidazole (I) polyamide conjugates 1 and 2 possessing a suberoylanilide hydroxamic acid (SAHA) moiety that is a strong inhibitor of histone deacetylase (HDAC). SAHA conjugate 2 was designed to target the promoter region of the p16 tumor suppressor gene. The DNA binding affinity of SAHA conjugate 2 to its target sequence was examined using surface plasmon resonance. HDAC inhibition activity of conjugates 1 and 2 was evaluated using a colorimetric assay. The results demonstrated that even though it possesses the relatively large SAHA moiety, conjugate 2 has high DNA sequence-specific binding properties and moderate HDAC inhibitory activity in vitro. SAHA conjugate 2 was found to cause morphological changes in HeLa cells and to induce selective Histone H3 lysine 9 acetylation.     

N-Heterocyclic carbene-catalyzed oxidations

N-Heterocyclic carbenes catalyze the oxidation of allylic and benzylic alcohols as well as saturated aldehydes to esters with manganese(IV) oxide in excellent yields. A variety of esters can be synthesized, including protected carboxylates. The oxidation proceeds under mild conditions, with low loadings of a simple triazolium salt pre-catalyst in the presence of base. Substrates containing potentially epimerizable centers are oxidized while preserving stereochemical integrity. The acyl triazolium intermediate generated under catalytic conditions can be employed as a chiral acylating agent in the desymmetrization of meso-diols.     

Key role of the Lewis base position in asymmetric bifunctional catalysis: design and evaluation of a new ligand for chiral polymetallic catalysts

New chiral ligands for asymmetric polymetallic catalysts were designed on the basis of the assumption that the higher-order assembly structure is stabilized by modifying the modular unit. The designed ligands 6 and 7 contained a scaffolding cyclohexane ring with a Lewis base phosphine oxide directly attached to the scaffold. A module in the polymetallic complex contains two metals per ligand, and a stable 6-, 5-, 5-membered fused chelation ring system should be generated. Synthesis of these ligands is simple and high yielding, using a catalytic dynamic kinetic resolution promoted by the Trost catalyst as a key step. Ligand function was assessed in a catalytic asymmetric ring-opening reaction of meso-aziridines with TMSCN, a useful reaction for the synthesis of optically active beta-amino acids. The Gd complex generated from Gd(OiPr)3 and the ligand was a highly active and enantioselective catalyst in this reaction. Enantioselectivity was reversed compared to the previously reported d-glucose-derived catalyst containing the same chirality of the individual module. ESI-MS analysis and X-ray crystallographic studies indicate that the assembly state of the modules in the polymetallic catalysts differs depending on the chiral ligand. The difference in the higher-order structure stems from a subtle change (one carbon) in the position of the Lewis base relative to the Gd metal. The change in the higher-order structure of the polymetallic complex led to a dramatic reversal of the enantioselectivity and increased catalyst activity.     

Channeling of Auroral Kilometric Radiation During Geomagnetic Disturbances

JETP Letters - The electromagnetic fields measured on the ERG satellite are presented and their comparative analysis with measurements on the WIND satellite is carried out. The possibility of...