Absolute stereostructures of cytotoxic metabolites, chaetomugilins A-C, produced by a Chaetomium species separated from a marine fish

Chaetomugilins A-C were isolated from a strain of Chaetomium globosum originally isolated from the marine fish Mugil cephalus, and their absolute stereostructures have been elucidated on the basis of spectroscopic analyses using 1D and 2D NMR techniques, some chemical transformations, and an X-ray analysis. This compound exhibited significant cytotoxicity against cultured P388 cells and HL-60 cells.     

Tetrahedral tellurate

A tetraethylammonium (TEA) salt of TeO 4 (2-) was synthesized by reacting Te(OH) 6 with tetraethylammonium hydroxide. X-ray structural analysis of (TEA) 2TeO 4.2H 2O confirmed that this new compound consists of discrete TeO 4 (2-) anions of distorted tetrahedral structure together with TEA cations and water molecules of crystallization [ a = 8.0820(9) A, b = 13.7730(12) A, c = 20.1590(18) A, V = 2244.0(4) A (3), Z = 4, and space group Pccb]. The (125)Te NMR spectrum indicated that water reacts with the TeO 4 (2-) anion to regenerate octahedral tellurate species in solution.     

N-spiro chiral quaternary ammonium bromide catalyzed diastereo- and enantioselective conjugate addition of nitroalkanes to cyclic alpha,beta-unsaturated ketones under phase-transfer conditions

[reaction, structure: see text] Conjugate addition of various prochiral nitroalkanes to cyclic alpha,beta-unsaturated ketones was found to be efficiently catalyzed by N-spiro C2-symmetric chiral quaternary ammonium bromide 1b possessing a 3,5-bis(3,4,5-trifluorophenyl)phenyl substituent under solid-liquid phase-transfer conditions to afford the corresponding gamma-nitro ketones in excellent chemical yields with unprecedented levels of diastereo- and enantiocontrol.     

Optically Active Helical Lanthanide Complexes: Storable Chiral Lewis Acidic Catalysts for Enantioselective Diels–Alder Reaction of Siloxydienes

Lanthanide triflates and a series of hexadentate chiral ligand complexes were synthesized. X‐ray‐quality crystals were obtained from mixtures of the lanthanide complexes, which were helical in shape. The complexes showed Lewis acidity and catalyzed the enantioselective Diels–Alder reaction of electron‐rich siloxydienes. The complexes were stable enough to be stored at ambient temperature on a laboratory bench and retained their Lewis acidity even after a month.     

First Stereoselective Total Synthesis of FD‐594 Aglycon

Stereocontrolled access to the hexacyclic core of FD‐594 has been achieved. The key steps include the intramolecular S_NAr reaction for construction of the densely functionalized xanthone skeleton, the stereoselective lactone cleavage using a chiral nucleophile to induce the axial stereochemistry, and the SmI₂‐mediated pinacol cyclization for the stereocontrolled conversion of axially chiral biaryl dialdehyde into the corresponding trans diol.

     

Computational study of radicals derived from hydroxyurea and its methylated analogues

Structural and electronic properties and chemical fate of free radicals generated from hydroxyurea (HU) and its methylated analogues N-methylhydroxyurea (NMHU) and O-methylhydroxyurea (OMHU) are of utmost importance for their biological and pharmacological effects. In this work the cis/trans conformational processes, tautomerizations, and intramolecular hydrogen and methyl migrations in hydroxyurea-derived radicals have been considered. Potential energy profiles for these reactions have been calculated using two DFT functionals (BP86 and B3LYP) and two composite models (G3(MP2)RAD and G3B3). Solvation effects have been included both implicitly (CPCM) and explicitly. It has been shown that calculated energy barriers for free radical rearrangements are significantly reduced when a single water molecule is included in calculations. In the case of HU-derived open-shell species, a number of oxygen-, nitrogen-, and carbon-centered radicals have been located, but only the O-centered radicals (e1 and z1) fit to experimental isomeric hyperfine coupling constants (hfccs) from EPR spectra. The reduction of NMHU and OMHU produces O-centered and N-centered radicals, respectively, with the former being more stable by ca. 60 kJ mol(-1). The NMHU-derived radical e4 undergoes rearrangements, which can result in formation of several conceivable products. The calculated hfccs have been successfully used to interpret the experimental EPR spectra of the most probable rearranged product 10. Reduction potentials of hydroxyureas, radical stabilization energy (RSE) and bond disocciation energy (BDE) values have been calculated to compare stabilities and reactivities of different subclasses of free radicals. It has been concluded, in agreement with experiment, that reductions of biologically relevant tyrosyl radicals by HU and NMHU are thermochemically favorable processes, and that the order of reactivity of hydroxyureas follows the experimentally observed trend NMHU > HU > OMHU.     

Direct identification of conformational isomers of adsorbed oligothiophene on Cu100

A direct conformational analysis using scanning tunneling microscopy (STM) has been performed for individual adsorbed alpha-octithiophene molecules on Cu(100). s-cis and s-trans conformational isomers are induced by the rotational flexibility of individual thiophene rings. By adding bulky N-silyl substituents to octithiophene, we successfully identify the s-cis and s-trans conformational isomers using STM. The obtained relative abundances of the s-cis and s-trans conformations are analyzed using ab initio molecular orbital calculations.     

Novel and efficient synthesis of cyanidin 3-O-beta-D-glucoside from (+)-catechin via a flav-3-en-3-ol as a key intermediate

[reaction: see text] A novel and efficient synthesis of cyanidin 3-O-beta-D-glucoside (1) was accomplished the first time by a biomimetic oxidation route. From (+)-catechin, 3-OH was glucosylated, and the 4-position of the nucleus was then oxidized and dehydrated to give the 5,7,3',4'-tetra-O-(tert-butyldimethylsilyl)flav-3-en-3-ol 3-O-glucoside (8) as a key intermediate. 8 was deprotected and oxidized under air in hydrogen chloride-MeOH to give 1.     

Microporous Silica Particles Prepared by the Salt-Catalytic Sol-Gel Process with Extremely Low Content of Water

Microporous silica was synthesized by the salt catalytic sol-gel process with extremely low content of water to tetramethoxysilane. Silica particles were precipitated even when the extent of hydrolysis was very low, since ammonium carbonate as a salt catalyst made the polycondensation faster than an acid catalyst. Microporous silica with a high surface area (680 m² g^–1) was obtained by combustion of methoxy groups at 450°C. The methoxy groups can be removed by the post-hydrolysis before heating. A high specific surface area (>750 m²g^–1) of microporous silica was obtained with pore diameter between 1.2 and 2.0 nm.     

Roles of porphyrin and iron metabolisms in the δ-aminolevulinic acid (ALA)-induced accumulation of protoporphyrin and photodamage of tumor cells

δ-Aminolevulinic acid (ALA)-induced porphyrin accumulation is widely used in the treatment of cancer, as photodynamic therapy. To clarify the mechanisms of the tumor-preferential accumulation of protoporphyrin, we examined the effect of the expression of heme-biosynthetic and -degradative enzymes on the ALA-induced accumulation of protoporphyrin as well as photodamage. The transient expression of heme-biosynthetic enzymes in HeLa cells caused variations of the ALA-induced accumulation of protoporphyrin. When ALA-treated cells were exposed to white light, the extent of photodamage of the cells was dependent on the accumulation of protoporphyrin. The decrease of the accumulation of protoporphyrin was observed in the cells treated with inducers of heme oxygenase (HO)-1. The ALA-dependent accumulation of protoporphyrin was decreased in HeLa cells by transfection with HO-1 and HO-2 cDNA. Conversely, knockdown of HO-1/-2 with siRNAs enhanced the ALA-induced protoporphyrin accumulation and photodamage. The ALA effect was decreased with HeLa cells expressing mitoferrin-2, a mitochondrial iron transporter, whereas it was enhanced by the mitoferrin-2 siRNA transfection. These results indicated that not only the production of porphyrin intermediates but also the reuse of iron from heme and mitochondrial iron utilization control the ALA-induced accumulation of protoporphyrin in cancerous cells.