Ethanol as a Hydrogenating Agent: Palladium-Catalyzed Stereoselective Hydrogenation of Ynamides To Give Enamides

Ethanol is shown to act as a hydrogenating agent for ynamides under palladium catalysis. This behavior is different from the normally expected reaction of ethanol addition to alkynes. The reaction shows stereoselectivity for E enamides, which is in contrast to reports using other hydrogenating sources. The method was also extended to ynamines. Alternatively, the use of ethanol and ammonium formate as the hydrogenating source gives Z enamides. The role of ethanol in hydrogenation was demonstrated by means deuterium labeling experiment.     

Chemical synthesis of the innate immune modulator – bacterial d-glycero-β-d-manno-heptose-1,7-bisphosphate (HBP)

The bacterial metabolite and potent innate immune modulator d-glycero-β-d-manno-heptose-1,7-bisphosphate (HBP) and its α-configured counterpart d-glycero-α-d-manno-heptose-1,7-bisphosphate were synthesized via stereoselective anomeric phosphorylation of the peracetylated d,d-heptose 7-dibenzylphosphate by exploiting different nucleophilicity of equatorial and axial lactols in the d-manno-series. We also report a novel approach for anomeric phosphorylation using modified Mitsunobu reaction conditions and provide the first full structural characterization of HBP. The first chemical synthesis of HBP offers access to an anomerically pure structurally defined probe for biological studies and to a lead compound operating as a powerful stimulator of intracellular signaling for possible therapeutic immunomodulation.     

Pressure-tuning of magnetism and linkage isomerism in iron(II) hexacyanochromate

A pressure-induced linkage isomerization of the cyanide anion has been observed in single crystals of a chromium(III)-iron(II) Prussian blue analogue of formula K0.4Fe4[Cr(CN)6]2.8 square1.2.16H2O (1). Upon application of pressure in the 0-1200 MPa range, the cyanide ligand rotates and becomes C-bonded to the iron(II) cations, leading to a stabilization of their diamagnetic low-spin states. The result is a decrease of magnetization and magnetic ordering temperatures from TC = 19 K at ambient pressure to 13 K at 1200 MPa. The initial magnetic properties can be restored on pressure release. The reversible movement of cyanide in the solid state can be exploited as a switch of the magnetic interaction at the molecular level.     

Acid-Catalyzed Condensation of Benzamide with Glyoxal,and Reaction Features

Scholars from around the world have been attempting to simplify and cheapen the synthetic method for the promising high-energy compound CL-20 for decades. The lack of understanding of the formation mechanisms of hexaazaisowurtzitane derivatives―CL-20 precursors―is a barrier to solving the said problems. Here, we report the results from an in-depth study into the acid-catalyzed condensation between benzamide and glyoxal in a molar ratio of 2:1 in polar protic and aprotic solvents. Sixteen compounds were isolated and identified, of which eight were synthesized for the first time. A geminal diol, N,N’-(2,2-dihydroxyethane-1,1-diyl)dibenzamide, was synthesized. Two isomers of 1,2-bis(benzoylamino)-1,2-ethanediol were isolated and identified. N,N’-(1-oxoethane-1,2-diyl)dibenzamide and 2-oxo-2-[(phenylcarbonyl)amino]ethyl benzoate were produced that were likely formed due to the 1,2-hydride shift. N-polysubstituted 1,4-dioxane-2,3,5,6-tetramine was synthesized for the first time, whose structure may be of interest as a scaffold for new explosives. DMSO, THF and HCOOH were found to be able to engage in a reaction with benzamide, or condensation products thereof, and glyoxal under acid-catalyzed conditions.     

Properties of spanning water networks at protein surfaces

The formation of a spanning two-dimensional hydrogen-bonded water network at the surface of proteins via a percolation transition enables their biological function. We show in detail how the spanning (percolating) water network appears at the surfaces of model hydrophilic spheres and at the surface of a single protein (lysozyme) molecule. We have found essential correlations of the linear extension, radius of gyration, and position of the center of mass of the largest water cluster with its size. The specific two-peak structure of the probability distribution of the largest cluster size allowed us to study various properties separately for spanning and nonspanning largest clusters. The radius of gyration of the spanning cluster always exceeds the radii of the spheres or the effective radius of the protein. Any spanning cluster envelops essentially more than half of the surface area. The temporal decay of the spanning networks shows a stretched exponential character. Their average lifetime at the percolation threshold is about the lifetime of a water-water hydrogen bond.     

The use of phosphine ligands to control the regiochemistry of Pd-catalyzed hydrostannations of 1-alkynes: synthesis of (E)-1-tributylstannyl-1-alkenes

The regiochemistry of palladium-catalyzed hydrostannations of terminal alkynes is dramatically influenced by ligand effects. Use of phosphines such as Cy3P, t-Bu2PCH2t-Bu, and t-Bu3P provides (E)-1-tributylstannyl-1-alkenes with regioselectivities up to >99:<1 for substrates where the commonly used Ph3P shows much lower regioselectivities.     

Synthesis and multiparameter sensor properties of the crown‐containing thiophene derivatives

A novel ditopic receptor was constructed as a combination of bisthiophene with pyridinylvinyl and crown‐containing styryl fragments. In the receptor, the pyridine residue was able to coordinate Fe²⁺, Cd²⁺, and Mg²⁺ metal cations, whereas the oxocrown ether moiety bound with the alkaline earth metal (Mg²⁺, Ca²⁺, and Ba²⁺) cations. ¹H NMR, optical, electrochemical, and ESI‐MS results provided conclusive evidence of a complex formation through both the coordination centers of the molecule. The obtained results showed that cation complexation induces optical and electrochemical changes, particularly for each binding center. This type of multiparameter sensor provides interesting perspectives for the future design of unique sensors, promising different analytical techniques. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis and characterization of polyamides obtained from tartaric acid and L-lysine

Two sets of AA · BB-type polyamides (PLyTA) were synthesized from natural compounds L-lysine and D- or L-tartaric acid via the active ester polycondensation method. The carboxyl and hydroxyl side groups were orthogonally protected as methyl ester and methyl ether, respectively. Direct reaction of methyl L-lysinate dihydrochloride with bis(pentachlorophenyl) di-O-methyl tartaric acid led to the aregic polyamide ar-PLyTA, whereas isoregic (ir-PLyTA) and syndioregic (sr-PLyTA) polyamides were obtained by polycondensation of specifically designed amide–aminoacid and amide–diamine monomeric precursors, respectively. These polyamides have intrinsic viscosities in the 0.50–0.76 dl g⁻¹ range, display optical activity, and are readily soluble in chloroform. They start to decompose well above 200 °C and display glass-transition temperatures at 100–105 °C. DSC and X-ray diffraction results indicated that these polyamides are not crystalline but they seem to adopt a partially ordered phase. No differences in properties other than optical rotation were observed between PLyTA made of D- and L-tartaric acid.     

How polar are ionic liquids? Determination of the static dielectric constant of an imidazolium-based ionic liquid by microwave dielectric spectroscopy

In a pilot study of the dielectric constant of room-temperature ionic liquids, we use dielectric spectroscopy in the megahertz/gigahertz regime to determine the complex dielectric function of five 1-alkyl-3-methylimidazolium salts, from which the static dielectric constant epsilon is obtained by zero-frequency extrapolation. The results classify the salts as moderately polar solvents. The observed epsilon-values at 298.15 K fall between 15.2 and 8.8, and epsilon decreases with increasing chain length of the alkyl residue of the cation. The anion sequence is trifluoromethylsulfonate > tetrafluoroborate approximately tetrafluorophosphate. The results indicate markedly lower polarities than found by spectroscopy with polarity-sensitive solvatochromic dyes.     

Determination of citrate in tablets and of oxytetracycline in serum using europium (III) luminescence

A direct method for the determination of citrate and oxytetracycline in samples containing complex matrices like tablets or serum has been developed using the luminescence of the ternary complex formed with Eu(III) ions. The triplet-state energy level of oxytetracycline (OxTc), the excitation maximum (412 nm) and the luminescence lifetime of Eu-OxTc (58 μs) were determined. A 17-fold luminescence enhancement at 615 nm occurs upon addition of citrate within a short 5-min incubation time at neutral pH. This is accompanied by a threefold increase of the luminescence decay time. The optimal conditions for determination of OxTc are equal concentrations of Eu (III) and citrate (C = 1 · 10^− 4 mol L^− 1) and pH 7.2. For determination of citrate, the optimal concentrations of Eu(III) and OxTc are 1 : 0.5 (C_Eu = 1 · 10^− 4 mol L^− 1, C_OxTc = 5 · 10^− 5 mol L^− 1) at pH 7.2. The linear range for determination of OxTc in serum is 0.25-250 μg mL^− 1, and for citrate in tablets from 0.5 to 10.0 μg mL^− 1 (2.3 · 10^− 6- 4 · 10^− 5 mol L^− 1). The detection limit was 0.1 μg mL^− 1 for OxTc and 0.2 μg mL^− 1 (1 · 10^-6 mol L^− 1) for citrate, respectively. A comparison of the new method with other methods for determination of citrate is given.