Rotational isomerism of a resveratrol tetramer, shoreaketone, in Shorea uliginosa

A new resveratrol tetramer, shoreaketone, was isolated from the stem bark of Shorea uliginosa (Dipterocarpaceae). The structure and the relative configuration were confirmed on the basis of 1D- and 2D-NMR spectral data. The structure has a novel framework of fused heptacyclic ring system including an α,β-unsaturated carbonyl group. In NMR spectra, shoreaketone is observed as two different conformers due to rotational isomerism.     

Synthesis and crosslinking reaction of poly(thiourethane)s having a siloxane moiety in the side chain

Poly(thiourethane)s having a siloxane moiety in the side chain were synthesized with a 5‐membered cyclic dithiocarbonate (DTC) having a siloxane group as a building block. The synthetic pathway consisted of (1) an addition reaction of the DTC with diamines and (2) polyaddition reactions of the resulting dithiols with diisocyanates. The siloxane moiety in the polymer side chain underwent a self‐condensation reaction upon exposure to moisture, and this led to a successful crosslinking reaction of the poly(thiourethane). The crosslinking on a silicate surface was accompanied by condensation between the siloxane side chain of the polymer and the silanol group on the surface, giving the corresponding surface that was permanently coated with the crosslinked polymer. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 6492–6502, 2005     

Origin of structural diversity in natural triterpenes: direct synthesis of seco-triterpene skeletons by oxidosqualene cyclase

At1g78500, one of the oxidosqualene cyclase (OSC) homologues from Arabidopsis thaliana, was expressed in a lanosterol synthase-deficient yeast strain and the products were analyzed. In addition to the known triterpenes, this OSC was found to produce two new triterpenes, the structures of which were determined by NMR and MS analyses. The new triterpenes are C-ring-seco-beta-amyrin (1) and C-ring-seco-alpha-amyrin (2) and named beta-seco-amyrin and alpha-seco-amyrin, respectively. beta-seco-Amyrin is produced from the oleanyl cation through bond cleavage between C8 and C14, and alpha-seco-amyrin is produced from the ursanyl cation in the same manner. Together with Grob fragmentation catalyzed by another OSC (marneral synthase) from A. thaliana, the formation of seco-amyrins by this OSC revealed that OSCs not only catalyze carbon-carbon bond formations and Wagner-Meerwein rearrangements but also cleave preformed ring systems in cationic intermediates. Based on this information, direct production of other natural seco-triterpenes by OSCs is proposed.     

Anionic alternating copolymerization of a bifunctional six‐membered lactone and glycidyl phenyl ether: Selective synthesis of a linear polyester having lactone moiety

An imidazole‐initiated copolymerization of an aromatic bislactone, 10‐methyl‐2H,8H‐benzo[1,2‐b:5,4‐b′]bipyran‐2,8‐dione ( 1 ), and glycidyl phenyl ether (GPE) was investigated. In spite of the bifunctional nature of 1 that would potentially permit formation of networked and thus insoluble polymers upon its copolymerization, only one of the two lactone moieties of 1 exclusively underwent the copolymerization to give a linear polyester. Spectroscopic analysis of the polyester and its reductive scission into the corresponding fragment revealed that the polyester was formed by a 1:1 alternating copolymerization of GPE and the lactone moiety of 1 . The other lactone in 1 that did not participate in the copolymerization was quantitatively incorporated into the side chain of the polyester as a reactive site, of which ring‐opening reactions by amine and alcohol as nucleophilic reagents allowed chemoselective polymer reactions. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1661–1672, 2009     

Clay dispersibility and mechanical property of the epoxy/clay nanocomposites prepared by different treatment methods

The bisphenol‐A type epoxy resin was combined with layered clays. Three types of epoxy/clay nanocomposites were prepared by different clay pretreatment methods, that is, the slurry (clay swelling with polar solvent), organo, and solubilization (organoclay swelling with polar solvent) methods. The organo and solubilization systems showed good dispersibility. The basal spacing of the layered clays in the obtained nanocomposites was evaluated by XRD and TEM observations. The basal spacing of the nanoclay in the solubilization system drastically increased. The mechanical properties were improved with the increase in the clay dispersion. A high modulus and fracture toughness were obtained by improvement of the clay dispersion into the matrix. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1753–1761, 2009     

Investigation of Novel Peptide Chiral Selectors Prepared by Solid-Phase Synthesis with a tert-Butoxycarbonyl Amino Acid

A new class of chiral stationary phases (CSP) with peptide chiral selectors was prepared by solid-phase synthesis with a tert-butoxycarbonyl-L-amino acid on silica. The type of amino acid that is favorable for this class of CSP is discussed. Using the CSP with the phenylalanine peptide selector, the effect of peptide length on the enantioselectivity was investigated in normal-phase mode. The applicability of the CSP with a phenylalanine peptide to chiral ligand-exchange chromatography was also examined.

     

Mixed-metal complexes incorporating platinum and lanthanide centers for selective binding and chirality sensing of succinates

A chromophoric platinum complex was combined with a nonacoordinated cyclen-lanthanide complex to give a new series of mixed-metal receptors. They specifically formed 1:1 complexes with dicarboxylates and offered selective chirality sensing of succinates.     

Lewis acid-catalyzed intramolecular amination via 1,3-chirality transfer

Direct intramolecular amination of the chiral non-racemic allylic alcohol 1 conjugated with a benzene ring afforded the tetrahydroisoquinoline 2 possessing a newly formed alkene in the presence of a catalytic amount of Lewis acid.     

Synthesis of 2,2a,4,5-tetraazabenz[cd] azulene derivatives

3-Methyl-1,8-dihydrocycloheptapyrazol-8-one hydrazone ( 5 ) reacted with triethyl ortho-formate, orthoacetate and orthopropionate to afford 2,2a,4,5-tetraazabenz[cd]azulene derivatives ( 7a-c ). 3-Methyl- ( 7b ) and 3-phenyl-substituted compounds ( 7d ) were also obtained by the reactions of 5 with acetyl and benzoyl chlorides, respectively.     

A theoretical study of the reactivity of Cu2O(111) surfaces: the case of NO dissociation

We compare the electronic properties of Cu(111) and Cu(2)O(111) surfaces in relation to the dissociation of NO using first principles calculations within density functional theory. We note a well-defined three-fold site on both O- and Cu-terminated Cu(2)O surfaces which is verified as the active site for the adsorption and dissociation of NO. The interaction of Cu with O atoms results in the forward shifting of the local density of states and formation of unoccupied states above the Fermi level, compared to the fully occupied d band of pure Cu. These results give valuable insights in the realization of a catalyst without precious metal for the dissociation of NO.