Synthesis of О-2-(acyl)vinylketoximes and their unusual rearrangements into 2- and 3-acyl-substituted pyrroles

О-2-(Acyl)vinylketoximes (freshly prepared from ketoximes and acylacetylenes in the presence of Ph₃P as catalyst in up to 83% yields) rearrange upon heating (125-150 °C) to give 2- or 3-acylpyrroles, wherein the positions of the acyl substituents do not correspond to known O-vinyloxime rearrangements; the chemo- and regioselectivity of the rearrangements depend on the reaction conditions. The described rearrangement enables syntheses of previously inaccessible substituted 2- or 3-acylpyrroles.     

Reactivity of Benzophenone O-Vinyloxime

Benzophenone O-vinyloxime readily takes up bromine and hydrogen chloride to give benzophenone O-(1,2-dibromoethyl)oxime and benzophenone O-(1-chloroethyl)oxime, respectively. Its reactions with methanol, trifluoroacetic acid, and acetic acid lead to formation of the corresponding O-(1-methoxyethyl), O-(1-trifluoroacetoxyethyl), and O-(1-acetoxyethyl) derivatives. Slow heating of the title compound induces its decomposition with formation of benzophenone as the major product; fast heating leads to a complex mixture of products containing benzophenone, benzophenone imine, and acetaldehyde.     

Unusual α-glycosylation with galactosyl donors with a C2 ester capable of neighboring group participation

Glycosylation of 4-methoxyphenyl 2,3,6-tri-O-benzoyl-β-d-glucopyranoside (2) with isopropyl 3-O-allyl-2,4,6-tri-O-benzoyl- (9) or 6-O-allyl-2,3,4-tri-O-benzoyl-1-thio-β-d-galactopyranoside (7) as the donor, afforded an α- and β-linked mixture, whereas with isopropyl 3-O-chloroacetyl-2-O-benzoyl-4,6-O-benzylidene- (13) and isopropyl 3-O-allyl-2-O-benzoyl-4,6-O-benzylidene-1-thio-β-d-galactopyranoside (15) as the donor, glycosylation of 2 gave α-linked products only, indicating that 4,6-O-benzylidenation led to α-stereoselectivity in spite of the C2 ester capable of neighboring group participation. Using 15 as the donor, glycosylation of mannose derivatives with 2- or 3-OH's, glucose with 2- or 3-OH's, galactose with 2-, or 3-, or 4-OH's, glucosamine and glucuronic acid with a 4-OH, and a lactose derivative with a 4-OH, also furnished α-linked products. However, when using 15 as the donor, glycosylation of aglycon alcohol or sugars with 6-OH's yielded normal β-linked products.     

Enhancement of O-GlcNAcylation on Mitochondrial Proteins with 2-(4-Methoxyphenyl)ethyl-2-acetamido-2-deoxy-β-d-pyranoside,Contributes to the Mitochondrial Network,Cellular Bioenergetics and Stress Response in Neuronal Cells under Ischemic-like Conditions

O-GlcNAcylation is a nutrient-driven post-translational modification known as a metabolic sensor that links metabolism to cellular function. Recent evidences indicate that the activation of O-GlcNAc pathway is a potential pro-survival pathway and that acute enhancement of this response is conducive to the survival of cells and tissues. 2-(4-Methoxyphenyl)ethyl-2-acetamido-2-deoxy-β-d-pyranoside (SalA-4g), is a salidroside analogue synthesized in our laboratory by chemical structure-modification, with a phenyl ring containing a para-methoxy group and a sugar ring consisting of N-acetylglucosamine. We have previously shown that SalA-4g elevates levels of protein O-GlcNAc and improves neuronal tolerance to ischemia. However, the specific target of SalA-4g regulating O-GlcNAcylation remains unknown. To address these questions, in this study, we have focused on mitochondrial network homeostasis mediated by O-GlcNAcylation in SalA-4g’s neuroprotection in primary cortical neurons under ischemic-like conditions. O-GlcNAc-modified mitochondria induced by SalA-4g demonstrated stronger neuroprotection under oxygen glucose deprivation and reoxygenation stress, including the improvement of mitochondrial homeostasis and bioenergy, and inhibition of mitochondrial apoptosis pathway. Blocking mitochondrial protein O-GlcNAcylation with OSMI-1 disrupted mitochondrial network homeostasis and antagonized the protective effects of SalA-4g. Collectively, these data demonstrate that mitochondrial homeostasis mediated by mitochondrial protein O-GlcNAcylation is critically involved in SalA-4g neuroprotection.     

Oxygen excess in the “114” cobaltite hexagonal structure: The ferrimagnet CaBaCo4O7.50

The study of the oxidation of the “114” orthorhombic cobaltite CaBaCo₄O₇, using first electrochemistry and then soft chemistry based on oxidation by NaClO, has allowed a new phase, CaBaCo₄O_7.50, to be prepared topotactically. The structural study of this phase shows that its hexagonal structure, closely related to that of orthorhombic CaBaCo₄O₇, is curiously similar to that of the members of the LnBaCo₄O₇ series, in spite of its excess oxygen. Its magnetic study shows that this phase, like CaBaCo₄O₇, is ferrimagnetic with the same T_C (60 K), but differently exhibits an unusual magnetic hysteresis. This exceptional behavior of CaBaCo₄O₇ with respect to oxidation as well as the magnetic properties of CaBaCo₄O_7.50 is interpreted in terms of the presence of defects due to oxidation.     

Self-sacrificing acetylation observed during attempted desilylation of 1-[4-benzenesulfonyl-3-O-(tert-butyldimethylsilyl)-2-deoxy-5-O-methanesulfonyl-α-l-threo-pentofuranosyl]thymine

Desilylation of 1-[4-benzenesulfonyl-3-O-(tert-butyldimethylsilyl)-2-deoxy-5-O-methanesulfonyl-α-l-threo-pentofuranosyl]thymine (4) with Bu₄NF/THF, when carried out at room temperature, gave four products. Among these, there were 1-[3-O-acetyl-4-benzenesulfonyl-2-deoxy-5-O-methanesulfonyl-α-l-threo-pentofuranosyl]thymine (7) and thymine. A possible reaction mechanism is proposed, which suggests the origin of 3′-O-acetyl group of 7 and thymine as well as structures of the other two products (9a and 9b).     

Stereoselective synthesis of all stereoisomers of vicinal and distal bis(O-2-aminoethyl)-p-tert-butylthiacalix[4]arene

O,O″- and O,O′-bis(2-aminoethyl)-p-tert-butylthiacalix[4]arenes of anti conformation have been prepared by the reduction of the corresponding O,O″- and O,O′-bis(cyanomethyl) ethers. Their syn-O,O″- and O,O′-counterparts have been prepared by alternative routes via the Mitsunobu reaction of thiacalix[4]arene with N-(2-hydroxyethyl)phthalimide and the reduction of a O,O′-disiloxanediyl-bridged O″,O?-bis(cyanomethyl) ether of 1,2-alternate conformation, respectively. These products are expected to serve as useful precursors of highly elaborated synthetic receptors, including biscalixarenes.     

Synthesis of an inherently chiral O,O′-bridged thiacalix[4]crowncarboxylic acid and its application to a chiral solvating agent

Treatment of readily available O,O′-1,1,3,3-tetraisopropyldisiloxane-1,3-diyl-bridged p-tert-butylthiacalix[4]arene (1) with tri(ethylene glycol) di-p-tosylate and subsequent desilylation gave O,O′-bridged thiacalix[4]crown 3 in an excellent yield. Mono-O-alkylation of 3 with ethyl bromoacetate, followed by optical resolution by chiral HPLC, and subsequent hydrolysis of the ester moiety gave inherently chiral O,O′-bridged thiacalix[4]crowncarboxylic acid (+)-6, which clearly discriminated enantiomeric primary amines, as well as amino esters, by ¹H NMR spectroscopy.     

Alkylation of 2-(methylsulfanyl)-6-polyfluoroalkylpyrimidin-4(3<Emphasis Type="Italic">H</Emphasis>)-ones with haloalkanes

The alkylation of ambident anions of 2-(methylsulfanyl)-6-(polyfluoroalkyl)pyrimidin-4(3H)-ones with 4-bromobutyl acetate leads to concurrent formation of O- and N-(4-acetoxybutyl) derivatives. Polar aprotic solvents favor formation of the O-isomer, and weakly polar dioxane favors N-alkylation. The reaction of 2-(methylsulfanyl)-6-(trifluoromethyl)pyrimidin-4(3H)-one with an equimolar amount of 1,2-dibromoethane in polar acetonitrile gives a mixture of N,N-, O,O-, and N,O-bridged bis-pyrimidines, as well as N- and O-[2-(methylsulfanyl)ethyl] derivatives, whereas in the presence of 10 equiv of 1,2-dibromoethane the N,O-isomer is formed as the only product. The reaction in weakly polar tetrahydrofuran yields N,N- and N,O-bispyrimidines.     

Subsolidus phase relations in the BaTiO3TiO2 system

Ba₆Ti₁₇O₄₀, Ba₄Ti₁₃O₃₀, BaTi₄O₉, and Ba₂Ti₉O₂₀ are the only compounds which were found to have a stability range in the subsolidus of the BaTiO₃TiO₂ system. BaTi₂O₅ and BaTi₅O₁₁, reported in other studies, apparently are not stable. The compound reported as Ba₂Ti₅O₁₂ appears to have been mistaken for Ba₆Ti₁₇O₄₀. X-Ray diffraction powder data are given for this phase which is monoclinic with a = 9.890, b = 17.117, c = 18.933 Å and β=98°42.6′. The phase formulated previously as BaTi₃O₇ is shown to be Ba₄Ti₁₃O₃₀ based on structural and density considerations, phase equilibria, and single crystal and powder X-ray diffraction data. This compound is orthorhombic with a = 17.072, b = 9.862, and c = 14.059 Å, probable space group, Cmca. An idealized structure for this phase is proposed. Ba₂Ti₉O₂₀ decomposes above 1300°C in the solid state to BaTi₄O₉ plus rutile. Single crystals were grown using BaF₂ as a mineralizer.     

Synthesis, structure and magnetic properties of V4O9—A missing link in binary vanadium oxides

V₄O₉: A missing link of Wadsley phases has been successfully synthesized by using sulfur as a reducing agent at a low temperature and its structure has been determined by combining electron, X-ray and neutron diffractions. V₄O₉ has an orthorhombic Cmcm structure and the lattice parameters are a=10.356(2) Å, b=8.174(1) Å and c=16.559(3) Å at room temperature. The structure is composed of shared edges and corners of three types of polyhedra; a VO₆ distorted octahedron, a VO₅ pyramid and a VO₄ tetrahedron. The structure of V₄O₉ is very similar to that of vanadyl pyrophosphate (VO)₂P₂O₇ which has PO₄ tetrahedra instead of VO₄ tetrahedra. This indicates that V₄O₉ is a salt of pyro-ion [V₂O₇]^4-; (VO)₂V₂O₇. The magnetic properties of V₄O₉ have been investigated by magnetic susceptibility, high-field magnetization and inelastic neutron scattering measurements. V₄O₉ is a quantum spin system with a spin-gapped ground state. The excitation gap between the singlet ground state and the excited triplet state is approximately 73 K. The magnetic susceptibility behavior suggests that V₄O₉ is a spin-1/2 dimer system with significant interdimer interactions, as opposed to (VO)₂P₂O₇, which is an alternating spin-1/2 chain system. This difference is thought to be due to the fact that VO₄-mediated interactions are considerably weaker than PO₄-mediated interactions.     

Structure de SnPb2O4 à quatre températures: relation entre dilatation et agitation thermiques

The structural study of SnPb₂O₄ oxide, an isomorphic compound belonging to the general family “MeX₂O₄” like Pb₃O₄, is made from accurate X-ray and neutron diffraction techniques on powdered samples. The structural evolution of SnPb₂O₄ is analyzed from 300 to 5 K: no phase transition is observed, contrary to Pb₃O₄, which exhibits a tetragonal → orthorhombic transition at 170 K. The thermal expansion tensor is practically isotropic in this temperature range: the α_a, α_c and α_V coefficients are neighboring those observed in the Pb₃O₄ tetragonal phase at the same temperature. On the other hand, the thermal vibrations are strongly anisotropic, with large amplitudes in the (a, b) plane. In this study the thermal vibrations are connected to the thermal expansion. $\text{B}\text{ab}$ and $\text{B}\text{c}$ temperature factors are considered as functions of the a and c cell parameters. The relation established by Grüneisen between the mean-square amplitudes of vibrations and the thermal volume expansion is discussed. The interatomic distances found show that the bindings are similar to that of Pb₃O₄: only the [Sn⁴⁺O₆] octahedrons are smaller than [Pb⁴⁺O₆] octahedrons.     

Group VB transition metal oxide clusters M4O n −/0 (M = Nb, Ta; n = 8–11): structural evolution and chemical bonding

The structural and electronic properties of two series of Group VB transition metal oxide clusters, M₄O _n ^? and M₄O _n (M = Nb, Ta; n = 8–11), are investigated using density functional theory calculations. Generalized Koopmans’ theorem is applied to predict the vertical detachment energies and simulate the photoelectron spectra. Large highest occupied molecular orbital–lowest unoccupied molecular orbital gaps are observed for these two stoichiometric M₄O₁₀ clusters and estimated to be 3.98 and 4.38 eV for M = Nb and Ta, respectively. The M₄O ₁₀ ^?/0 (M = Nb, Ta) clusters are polyhedral cage structures with high symmetry (T _d for the neutral and D _2d for the anion) in which each metal atom joints three bridging and one terminal O atoms. For the Nb oxide species, Nb₄O ₈ ^?/0 and Nb₄O ₉ ^?/0 can be viewed as removing two and one terminal O atoms from Nb₄O ₁₀ ^?/0 , respectively. The Ta species follow the same rule to the Nb species, except that the anionic Ta₄O₈ ^? is formed by removing one terminal and one bridging O atoms from Ta₄O₁₀ ^?. The Ta₄O₉ containing a localized Ta³⁺ site can readily react with O₂ to form the Ta₄O₁₁ which can also be viewed as replacing a terminal oxygen atom in Ta₄O₁₀ by a peroxo O₂ unit, whereas the added oxygen atom is found to be a bridging one in the O-rich clusters Nb₄O ₁₁ ^?/0 and the anionic Ta₄O₁₁ ^?. Molecular orbital analyses are performed to analyze the chemical bonding in the tetra-nuclear metal oxide clusters and to elucidate their structural and electronic evolution.     

Nanosized temperature-responsive Fe3O4-UA-g-P(UA-co-NIPAAm) magnetomicelles for controlled drug release

This paper demonstrated the preparation of temperature-responsive magnetomicelles that consist of a functionalized hexagonal magnetic core, Fe₃O₄-undecylenic acid (Fe₃O₄-UA), and an amphiphilic surface layer of temperature-responsive polymer. The functionalized magnetic Fe₃O₄-UA core was prepared by a suspension-oxidation reaction in an aqueous solution, during which the formation of the Fe₃O₄ and coordination of UA to the Fe₃O₄ occurred simultaneously. Amphiphilic poly(undecylenic acid-co-N-isopropylacrylamide) (P(UA-co-NIPAAm)) was grafted to the Fe₃O₄-UA core as a temperature-responsive micellar surface layer to prepare well dispersed Fe₃O₄-UA-g-P(UA-co-NIPAAm) magnetomicelles with the size of around 8 nm in water. The application of resulted nanosized Fe₃O₄-UA-g-P(UA-co-NIPAAm) magnetomicelles in controlled drug delivery was further investigated and it was found that resulting magnetomicelles exhibited good potential for temperature triggered controlled drug release.     

Single-crystal synthesis, structure analysis, and physical properties of the calcium ferrite-type NaxTi2O4 with 0.558<x<1

Single crystals of calcium ferrite CaFe₂O₄-type NaTi₂O₄ having millimeter-sized needle shapes were synthesized by a reaction of Na metal and TiO₂ in a sealed iron vessel at 1473 K. Sodium-deficient Na_xTi₂O₄ single crystals with 0.558<x<1 were successfully synthesized by a topotactic oxidation reaction using NaTi₂O₄ single crystals as parent materials. The crystal structures of Na_xTi₂O₄ with x=0.970, 0.912, 0.799, 0.751, 0.717, 0.686, 0.611, and 0.558 were determined by the single-crystal X-ray diffraction method. The basic framework constructed by the Ti1O₆ and Ti2O₆ double rutile chains was maintained in these Na_xTi₂O₄ compounds. Based on the results of bond valence analysis, we speculated that the Ti1 sites are preferentially occupied by Ti³⁺ cations over the compositional range of 0.8<x<1, while both the Ti1 and Ti2 sites are randomly occupied by Ti³⁺ and Ti⁴⁺ cations at x=0.558. Magnetic susceptibility data indicated that the broad maximum around 40 K observed in as-grown NaTi₂O₄ is suppressed by an Na deficiency and vanishes in Na_0.717Ti₂O₄. The electrical resistivity increased with the Na deficiency; however, it was still semiconductive in Na_0.799Ti₂O₄.     

Two novel carbonic acid esters conjugated with oligophenyl glucosides from Rhamnus nakaharai

Two novel carbonic acid esters conjugated with oligomeric phenyl glycosides have been isolated and characterized from the wood of Rhamnus nakaharai. The structures are characterized as 5,7-dihydroxyphthalide 5-O-β-[6-O-{3″-methoxy-4″-O-β-[6?-O-(4?-O-carboxy-3?,5?-dimethoxy)phenyl]glucopyranosyl}phenyl]glucopyranoside (1) and 6-O-{3′-methoxy-4′-O-β-[6″-O-(3?-mercapto-5?-methoxy-4?-O-methylcarboxy)phenyl]glucopyranosyl}phenyl β-glucopyranose (2), namely, rhamnakoside A (1) and B (2), all by NMR and other spectral methods, respectively. They could be a novel case of phase II detoxification products and biogenetic diversity in plant kingdom.     

Synthesis of an aryl 2-deoxy-β-glycosyl tetrasaccharide to probe retaining endo-glycosidase mechanism

The synthesis of the 1,3–1,4-β-glucanase substrate analogue 4-nitrophenyl O-β-d-glucopyranosyl-(1→4)-O-β-d-glucopyranosyl-(1→4)-O-β-d-glucopyranosyl-(1→3)-2-desoxi-β-d-glucopyranoside 2 is reported. Starting from the main tetrasaccharide obtained by enzymatic depolymerization of barley β-glucan, the synthetic scheme involves preparation of the corresponding 3-O-substituted glycal which was converted into a 2-deoxy-α-glycosyl iodide as a glycosyl donor. The key glycosylation step was successfully achieved by nucleophilic substitution of the iodide donor with 4-nitrophenolate with high β-selectivity.     

Fabrication of 1D Fe3O4/P(NIPAM-MBA) thermosensitive nanochains by magnetic-field-induced precipitation polymerization

One-dimensional (ID) magnetic thermosensitive Fe₃O₄/poly(N-isopropylacrylamide–N,N′-methylenebisacrylamide) (P(NIPAM-MBA)) peapod-like nanochains have been successfully synthesized by magnetic-field-induced precipitation polymerization using Fe₃O₄ as building blocks and P(NIPAM-MBA) as linker. Fe₃O₄ microspheres can be arranged with the direction of an external magnetic field in a line via the dipolar interaction between Fe₃O₄ microspheres and linked permanently via P(NIPAM-MBA) coating during precipitation polymerization. 1D magnetic Fe₃O₄/P(NIPAM-MBA) peapod-like nanochains can be oriented and aligned along the direction of the external magnetic field. More interestingly, Fe₃O₄ microspheres in each peapod were regularly arranged in a line and periodically separated through the P(NIPAM-MBA) layers with a visible interparticle spacing.     

Polyèdre de coordination de l'etain(II) dans SnC2O4: Relations structurales entre SnC2O4, Na2C2O4 et Na2Sn(C2O4)2

The crystal structure of SnC₂O₄ has been determined by X-ray single-crystal techniques and refined to R = 0,018 for 1139 reflections. The cell is monoclinic, space group $\text{C2}\text{c}$ with Z = 4 formula units, the parameters being a = 10,375(3)Å. b = 5,504(2)Å, c = 8,234(3)Å, β = 125,11(2)°. The oxalato groups, located on symmetry centers, are chelated to two Sn atoms through one oxygen on each carbon atom, giving rise to an infinite string (SnC₂O₄)_n. The Sn(II) atom is one-side bonded to four oxygen atoms with two SnO bonds of 2,232(2) Å and two of 2,393(2) Å. The tin atom is in a distorted trigonal bipyramid SnO₄E, the lone pair E occupying one of the apices of the equatorial trigonal base of the polyhedron. Crystal structure comparison with disodium bisoxalatostannate(II), Na₂Sn(C₂O₄)₂, permits one to deduce SnC₂O₄ by crystallographic shear operation $\text{1}\text{8}\text{[34}\text{2}\text{](001)}$ of $\text{c}\text{2}$ periodicity. Na₂Sn(C₂O₄)₂ can be described as an intergrowth of SnC₂O₄ and Na₂C₂O₄ structures and consldered as the first member of a new series Na₂Sn_1+n(C₂O₄)_2+n with n integer ? 0.     

Organofluorine compounds and fluorinating agents

Starting with 1,2,4,6-tetra-O-acetyl-3-O-dodecyl-β-d-glucose (1), mixed alkyl-perfluoroalkyl substituted sugar derivatives with an anomeric perfluoroalkylthio group and an O-alkyl group in the 3 position were synthesized via 2,4,6-tri-O-acetyl-3-O-dodecyl-1-thio-β-d-glucose (4). The latter was S-perfluorohexylated with 1-iodoperfluorohexane in a dithionite initiated reaction yielding perfluorohexyl 2,4,6-tri-O-acetyl-3-O-dodecyl-1-thio-β-d-glucopyranoside (5). Experiments with the aim compound 5 completely to deacetylate ended in surprising results. Thus, methanolic methanolate solution produced the orthoester 7 as the result of α-fluoride replacement by methoxy groups as well as the methyl glucoside 8 as the result of a transglycosylation reaction. Alumina supported cesium fluoride cleaved regioselectively the two acetyl groups in the 4- and 6-position yielding perfluorohexyl 2-O-acetyl-3-O-dodecyl-1-thio-β-d-glucopyranoside (10). A complete deacetylation of 5 to amphiphile 11 succeeded only with methanolic tert-butanolate. However, the products 8 and 10 were likewise formed.