Chemical constituents from the fruiting bodies of Phellinus igniarius

A new tirucallane-type triterpenoid igniarine (1), and four known compounds meshimakobnol A (2), meshimakobnol B (3), ergosterol (4) and ergosterol peroxide (5), were purified from the methanol extracts of the fruiting bodies of Phellinus igniarius (DC. ex Fr.) Quél. The structure of 1 was elucidated using a combination of 1D and 2D NMR techniques and HR-ESI-MS analyses. In addition, the isolated compounds were examined for their cytotoxicity against several tumour cell lines and part of the tested compounds demonstrated weak cytotoxicity.     

Stable splittings of

Using the Snaith-Mitchell-Priddy splittings of and , we can give new stable splittings of and
respectively.

     

On nonlinear -widths

For characterization of best nonlinear approximation, DeVore,
Howard, and Micchelli have recently suggested the nonlinear -width of a subset in a normed linear space . We proved by a topological method that for and the well-known Aleksandrov -width in a Banach space the following inequalities hold: . Let be the unit ball of Besov space , of multivariate periodic functions. Then for approximation in , with some restriction on and , we established the asymptotic degree of these -widths: .

     

Crystal Structure of [Co2(μ-dmg)2(μ-dmg H)(dmg H)(Pø3)] 1/2 dmg H2 · 1/2 CH3OH: A Crystal Containing Various Forms of dmg Ligand

The crystal structure of [Co₂(μ-dmg)₂(μ-dmg H)(dmg H)(Pø₃)] · 1/2 dmg H₂ · 1/2 CH₃OH has been determined by single crystal X-ray diffraction. The title complex crystallizes in triclinic space group P&1bar; with a=10.859(3), b=13.299(3), c=15.247(3)Å, α=98.52(2), β=99.26(2), γ=97.80(2)° and Z=2. The agreement indices are R(F)=0.062 and R_w(F)=0.085 for 5231 observations and 515 variables. Both cobalt atoms have an oxidation state of 3+ and are both six-coordinated; one Co(III) atom is bonded to a phosphorous atom of triphenylphosphine, four nitrogen atoms of two planar ligands, dmg^2? and dmgH^?, and one oxygen atom of another dmg^2? ligand. The other Co(III) atom is coordinated by four nitrogen atoms of two cis nonplanar ligands, dmg^2?, dmgH^?, and two oxygen atoms of the other dmg^2? and dmgH^? ligands. There are three N-O bridged ligands namely two dmg^2? and one dmgH^? between two Co(III) atoms. A free molecule of dmgH₂ and a molecule of CH₃OH are also found in the crystal lattice. The structure interestingly demonstrates the possible various forms of dmg, not only on their charge but also in different conformations upon coordination.     

Squash inhibitors: from structural motifs to macrocyclic knottins

In this article, we will first introduce the squash inhibitor, a well established family of highly potent canonical serine proteinase inhibitors isolated from Cucurbitaceae. The squash inhibitors were among the first discovered proteins with the typical knottin fold shared by numerous peptides extracted from plants, animals and fungi. Knottins contain three knotted disulfide bridges, two of them arranged as a Cystine-Stabilized Beta-sheet motif. In contrast to cyclotides for which no natural linear homolog is known, most squash inhibitors are linear. However, Momordica cochinchinensis Trypsin Inhibitor-I and (MCoTI-I and -II), 34-residue squash inhibitors isolated from seeds of a common Cucurbitaceae from Vietnam, were recently shown to be macrocyclic. In these circular squash inhibitors, a short peptide linker connects residues that correspond to the N- and C-termini in homologous linear squash inhibitors. In this review we present the isolation, characterization, chemical synthesis, and activity of these macrocyclic knottins. The solution structure of MCoTI-II will be compared with topologically similar cyclotides, homologous linear squash inhibitors and other knottins, and potential applications of such scaffolds will be discussed.     

A flavonoid bioside ofOxytropis strobilaceae

Chemistry of Natural Compounds -     

Integrated Systems for Water Cleavage by Visible Light; Sensitization of TiO2 Particles by Surface Derivatization with Ruthenium Complexes

Irradiation of acidic (pH 2) solutions of RuL₃²⁺ 2Cl^? (L = diisopropyl 2,2′-bipyridine-4,4′ -dicarboxylate) in the presence of TiO₂ at 100°C leads to the loss of one bipyridyl ligand and the chemical fixation of RuL₂ at the surface of teh TiO₂ particles through formation of Ru-O-Ti bonds. These surface complexes are very stable and shift the absorption onset of TiO₂ beyond 600 mm. Efficient sensitization H₂-generation is achieved with this system beginning in the wave length domain between 590 and 665 nm. Preliminary water cleavage experiments with bifunctional TiO₂/Pt/RuO₂ redox catalyst are reported.     

Castelnuovo–Mumford Regularity of Associated Graded Modules and Fiber Cones of Filtered Modules

We give bounds on the Castelnuovo–Mumford regularity of the associated graded module of an arbitrary good filtration and of its fiber cone. These bounds extend previous results of Rossi–Trung–Valla and Linh.     

Efficient and green synthesis of 4H-pyran derivatives under ultrasound irradiation in the presence of K2CO3 supported on acidic montmorillonite

Acid-treated montmorillonite coating with K₂CO₃ is used as a catalyst for an efficient, rapid, one-pot synthesis of 4H-pyran derivatives in good yield under ultrasonic irradiation. The catalyst is environmentally benign, easy handling, nontoxic, stable in air, and inexpensive.     

Use of evaporative light scattering detector in the detection and quantification of enantiomeric mixtures by HPLC

Routinely used in our laboratories at analytical scale, an evaporative light scattering detector (ELSD) has proved to be versatile in the detection of enantiomeric resolution using chiral stationary phases by HPLC. Though this kind of detector has been widely used in various domains, its application in enantiomeric resolution has not been discussed in the literature and is found to have very specific features especially in the quantitative perspective. In contrast with the UV detection, the peak area from ELSD for both enantiomers of a racemic mixture may not be the same. This complicates the assessment of the enantiomeric purity of unknown samples. This current work deals with some practical aspects in the detection of enantiomers and in accurate quantitative determination of enantiomeric purity by ELSD. Effects of analyte nature (more precisely molecular weight and volatility), peak shape and peak shape difference between enantiomers on the quantitative integration by ELSD are discussed in connection with the UV-detection results. The calibration for quantitative enantiomeric analysis and its effectiveness are demonstrated.