Incorporation of D-glucosamine alkyi glucopyranosides into the bilayer of small unilamellar vesicles of egg phosphatidyl choline

Alkyl 2-acetamido-2-deoxy-β-d-glucopyranosides were incorporated into the phospholipid bilayer of small unilamellar vesicles. Depending on the lengths of the alkyl aglycone group (C₈–C₁₄), the carbohydrate was either found in the form of micelles (C₈) or was effectively incorporated in the bilayer (C₁₄). The use of radiolabelled lipids and/or carbohydrates enabled the quantitative determination of the amounts of lipid and carbohydrate recovered into the vesicles. An enzymatic assay has been carried out to evaluate the outer and inner distribution of the carbohydrate moieties on the liposomes.     

Metabolites of microorganisms. Aranciamycin

Aranciamycin is a new antibiotic isolated from cultures of a strain of Streptomyces echinatus. The orange-yellow acidic compound, C₂₇H₂₈O₁₂, is a glycoside of an aglycone, aranciamycinone, and a 6-deoxyhexose monomethyl ether. The aglycone, C₂₀H₁₆O₈, is composed of a 1, 8-dihydroxyanthraquinone nucleus, to which a fourth carbocyclic six-membered ring is condensed, bearing a tertiary C-methyl group, a tertiary and a secondary hydroxyl group, a secondary methoxyl group, and a carbonyl group. A partial formula of the aglycone is given. Aranciamycin as well as its aglycone are strongly inhibitory against gram-positive bacteria on synthetic media. The antibiotic activity is considerably decreased by the addition of amino-acid combinations and pyruvate to the test medium.     

Glycosides of marine invertebrates. XXVI. Holothurin A from the Pacific Ocean holothurianHolothvria squamifera. Isolation of the native aglycone

The known triterpene tetraoside holothurin A has been isolated from the Pacific Ocean holothurianHolothuria squamifera. By using two independent methods — enzymatic cleavage and two-stage Smith degradation — 22,25-epoxyholost-9(11)-ene-3β,12α,17α-triol, C₃₀H₄₆O₆, which is the native aglycone of holothurin A, was obtained. The structure of the native aglycone has been established on the basis of the results of IR, mass, and PMR spectroscopy.     

Über triterpene—XXIX : Zur struktur des avenacins

From the roots of oat (Avena sativa) a second antibiotic active glycoside, avenacine B, was isolated in addition to the main glycoside avenacine A. In the aglycone of A the double bond could not be established contrary to the statement in the literature but an aldehyde group in addition to the keto group was identified and therefore the proposed structure has to be revised. In the aglycone of B the —CH₂OH-group of A has been substituted by CH₃. The structures of the sugar chains in both glycosides have been determined, in avenacine A as [β-d-gluco-pyranosyl(1 → 4)-[β-d-glucopyranosyl (1 → 2)]-α-l-arabinosyl (1)- and in B as [β-d-glucopyranosyl (1 → 4)]-β-d-glucopyranosyl (1)-.     

A Comparative PMR study of Exchange reactions in organo- Mercury, -TIN and -LEAD derivatives of some thiols

Metal—proton and metal—metal exchange reactions have been studied by PMR for thiophenol, 2-methylthiophenol, 2,6-dimethylthiophenol, benzyl mercaptan and their C₆H₅HG, (C₆H₅)₃Sn and (C₆H₅)₃Pb derivatives in chlorobenzene and pyridine solutions. In chlorobenzene the metal—metal exchange has been found to proceed in many cases at a greater rate than the metal—proton type, the exchange mobility of hydrogen and organometallic groups in chlorobenzene increasing in the order (C₆H₅)₃Sn<H<(C₆H₅)₃Pb<C₆H₅Hg. In the case of the (C₆H₅)₃Sn and (C₆H₅)₃Pb groups, pyridine accelerates the metal—proton exchange to a greater extent than the metal—metal exchange.The influence of various factors on the exchange reactions has been studied Analysis of the experimental findings and literature data has led to the conclusion that most probably the mechanism of the exchange reactions involves an associative pathway, the ease of exchange being mainly determined by the ability of the migrating group to form a cyclic transition state with delocalized bonds. The data on the exchange equilibria of the organometallic derivatives of 2-methylthiophenol and 2,6-dimethylthiophenol with thiophenol and its derivatives demonstrate that the C₆H₅HgS, (C₆H₅)₃SnS and (C₆H₅)₃PbS groups have equal steric requirements when involved in non-bonded interactions with o-methyl substituents.     

Fast atom bombardment mass spectrometry of non-volatile organometallic compounds. Rhodium,iridium and platinum complexes containing a cumulene ligand

Fast atom bombardment (FAB) mass spectrometry has been used to examine a series of rhodium, iridium and platinum organimetallic complexes, in which a cumulene ligand is attached to the metal in either σ-or π-bonding fashion. The most intense ion formed in the rhodium and platinum series is the metal-bis(triphenylphosphine) ion, while the [Ir(P(C₆H₅)₃)₂CO]⁺ ion is most intense for the iridium series. The platinum complexes show the most intense molecular ion peaks (up to 35% relative intensity), while the rhodium complexes show the least intense molecular ion peaks. The primary fragmentations of all these complexes occur at the metal-ligand bonds. The cumulenic ligand is lost as an impact unit in all cases. The FAB mass spectra of Rh(P(C₆H₅)₃)₃Cl (Wilkinson's catalyst), Ir(P(C₆H₅)₃)₂COCl (Vaska's compound), Rh(P(C₆H₅)₃)₂COCl and Pt(P(C₆H₅)₃)₂(C₂H₄)–synthetic precursors or related compounds to the organometallic complexes examined here–are included for comparison.     

Spectra and structure of gallium compounds: Part VII. Microwave,infrared and raman spectra and normal coordinate analysis of trimethylamine-trimethylgallane

The infrared (100–3500 cm^?1) and Raman (25–3200 cm^?1) spectra of the solid phases of (CH₃)₃NGa(CH₃)₃ and (CH₃)₃¹⁵NGa(CH₃)₃ have been recorded near liquid nitrogen temperatures as well as the Raman spectrum (100–3200 cm^?1) of the liquid phase at ~50°C and the low resolution microwave spectrum (26.5–39.0 GHz) of (CH₃)₃NGa(CH₃)₃. The spectra have been interpreted on the basis of C_3v molecular symmetry and a vibrational assignment is proposed for all but the torsional modes. The B value calculated from the microwave spectrum is consistent with published structural parameters reported from an electron diffraction study. A modified valence force field has been used to calculate the observed frequencies and the potential energy distribution. The force constants presented are consistent with changes in the structural parameters of the Lewis acid and base upon adduct formation. Extensive mixing has been observed among the low-frequency modes. The Ga-N stretching force constant (1.6 mdyn A^?1) has a value intermediate between those of (CH₃)₃NGaH₃ and H₃NGa(CH₃₃).The lack of apparent factor group splitting indicates that only one molecule occupies each primitive cell, situated on either a C₃ or C_3v site. A rhombohedral space group such as R3m(C⁵_3v) is consistent with these observations.     

Thermodynamics of vaporization of some cyclic perfluorocarbons

The temperature dependence of the saturation vapor pressure of perfluoro-meta-dimethylcyclohexane, (CF₃)₂C₆F₁₀, has been determined by the ebulliometric method in the moderate pressure range from 8.4 to 101.6 kPa. Enthalpies of vaporization have been obtained calorimetrically for perfluorobicyclo(4,4,0)dec(1,6)ene, C₁₀F₁₆, and (CF₃)₂C₆F₁₀ at T = 298.15 K. Densities of C₁₀F₁₆ have been measured in the small temperature range from 293 to 338 K. Critical parameters have been estimated from vapor pressure data and densities for the substances under study and for some mono- and bicyclo-perfluorocarbons investigated earlier. A second-order group additivity method has been applied to predict the vaporization enthalpies of some cyclic perfluorocarbons.     

Structural characterization and identification of oleanane-type triterpene saponins in Glycyrrhiza uralensis Fischer by rapid-resolution liquid chromatography coupled with time-of-flight mass spectrometry

Oleanane‐type triterpene saponins (OTS) are major active ingredients in Glycyrrhiza uralensis. In this work, a rapid‐resolution liquid chromatography with time‐of‐flight mass spectrometry (RRLC/TOF‐MS) method has been developed to characterize and identify OTS from G. uralensis. The major diagnostic ions and fragmentation pathways from thirteen OTS have been characterized for the first time. At a low fragmentor voltage of 120 V in positive ion mode, the precursor ion [M + H]⁺ or/and [M + Na]⁺ was obtained for accurate determination of molecular formula. When the fragmentor voltage was increased to 425 V, abundant characteristic fragment ions were observed for structural characterization. Neutral losses of sugar moieties, such as glucuronic acid (GlcA, 176 Da), glucose (Glc, 162 Da) and rhamnose (Rha, 146 Da), were commonly observed in the MS spectra for prediction of the sugar number and sequences. Other typical losses included AcOH (60 Da), CH₂O (30 Da), 2 × H₂O (2 × 18 Da) and HCOOH (46 Da) from [Aglycone + H–H₂O]⁺ (named [B]⁺), corresponding to the presence of a C₂₂‐acetyl group, C₂₄‐hydroxyl group, C₂₂‐hydroxyl group or C₃₀‐carboxyl group on the aglycone moiety, respectively. In particular, characteristic ring cleavages of the aglycone moieties on A‐ and B‐rings were observed. Based on the fragmentation patterns of reference compounds, nineteen OTS have been identified in an extract of G. uralensis, thirteen of which were unambiguously identified and the other six were tentatively assigned. Copyright © 2010 John Wiley & Sons, Ltd.     

Studies on the role of oxidation states of the platinum surface in electrocatalytic oxidation of small primary alcohols

The role of the oxidation state of a platinum polycrystalline surface in the electrocatalytic oxidation of C₁ to C₄ primary alcohols has been studied by using electrochemical techniques, in situ FTIR spectroscopy and X-ray photoelectron spectroscopy. The results revealed that the oxidation state of the Pt surface plays a key role in the oxidation of primary alcohols, and demonstrated that the oxidation of C₁ to C₄ primary alcohols on a Pt electrode is controlled by the formation of surface oxides on the Pt electrode at different potentials. It was found that the dependence of the reaction process on the oxidation states of the platinum surface yielded similar features in the cyclic voltammogram for oxidation of different primary alcohols at a Pt electrode. According to the effects in the oxidation of primary alcohols, the surface oxides of platinum may be classified as active and poison species. The Pt surface oxides of higher oxidation states (Pt(OH)₃ and PtO₂) formed at potentials above 1.0 V (SCE) were identified as poison species, while other lower oxidation states of Pt surface oxides such as PtOH, Pt(OH)₂ and PtO may be identified as the possible active species for primary alcohol oxidation.     

Phosphaniminato-Komplexe Seltener Erden. Synthese und Kristallstrukturen von [M2(C5H5)3(NPPh3)3] · 3 C7H8 mit M = Y,Dy und Er. Magnetische Eigenschaften von [Dy2(C5H5)3(NPPh3)3] · 3 C7H8

Phosphoraneiminato Complexes of Rare Earths Elements. Syntheses and Crystal Structures of [M₂(C₅H₅)₃(NPPh₃)₃] · 3 C₇H₈ mit M = Y, Dy, and Er. Magnetic Properties of [Dy₂(C₅H₅)₃(NPPh₃)₃] · 3 C₇H₈ The title compounds have been prepared by reactions of the cyclopentadienidchlorides [M(C₅H₅)₂Cl]₂ with LiNPPh₃ in boiling toluene, and they were characterized by crystal structure determinations. All three compounds crystallize isotypicly with one another within the orthorhombic space group Pbca with Z = 8. Two of the three phosphoraneiminato groups link the metal atoms via μ₂-N atoms to almost planar M₂N₂ four-membered rings. The third NPPh₃^– group is terminally bonded. The magnetic susceptibility of [Dy₂(C₅H₅)₃(NPPh₃)₃] · 3 C₇H₈ has been determined (SQUID magnetometer) in the temperature range 1.7 K–300 K at magnetic fields between 0.01 T and 5 T. Calculations based on a cubic ligand field model lead to a satisfactory simulation with reasonable ligand field parameters. The inclusion of isotropic intramolecular exchange interactions in the model does not improve the fit, so that in the framework of the applied model no hints to a spin-spin coupling within the dinuclear units are obtained.     

Mechanism of reductive elimination of benzonitrile in cyanophenyl complexes of nickel(II) : II. Reactions of [cyano(phenyl)bis(tricyclohexylphosphine)nickel(II)]

The thermal decomposition of the complex Ni(CN)(C₆H₅)(PCy₃)₂ (Cy = cyclohexyl) in decalin has been examined. The complex reacts with P(OC₂H₅)₃ to give C₆H₅CN in quantitative yield. The mechanism of this reaction has been investigated and compared with that of the similar reaction shown by Ni(CN)(C₆H₅)(PEt₃)₂. The results indicate that the easiest path for the reaction involves a bimolecular attack of P(OC₂H₅)₃ at the metal atom before reductive elimination of C₆H₅CN.     

Algebraic symmetry and determination of the “imaginary” crystal field parameters from optical spectra of fn-ions. Hexagonal and trigonal symmetry

Algebraic symmetry of the characteristic equation of the crystal field hamiltonian Ĥ_CF for hexagonal (C₆, C_3h, C_6h) and trigonal (C₃, S₆) symmetry is considered. Explicit dependence of the coefficients a_i of the characteristic equation on the CF parameters is derived by ALTRAN. Magnitudes, signs and/or relative signs of the CF parameters which can be determined from fitting the optical spectra of fⁿ-ions at sites of the above symmetry are established. The algebraic results derived here can facilitate the fitting procedures for any hexagonal and trigonal symmetry. The relevant literature is extensively surveyed. The approach C (complete) to fitting the optical spectra, which yields ambiguous and unreliable results in general, has not been employed to hexagonal (C₆, C_3h, C_6h) symmetry. Some misinterpretations on the approach R (reduced) and A (approximated), which merge for this symmetry, are clarified. Crystal field analysis has been carried out for trigonal (C₃, S₆) symmetry in but a few cases only. The survey has revealed one case of the inappropriate C used for Eu³⁺ in the trigonal (C₃) Eu(DBM)₃ · H₂O system.     

A Simple Synthesis of C-Glucosides Related to the Antitumor Agent Etoposide

Abstract

The synthesis of four new lignan derivatives 2a, 2b, 3a and 3b related to the anticancer agent etoposide has been accomplished. In these compounds a methylene or ethylene group of a C-glucoside separates the glucosidic moiety as present in etoposide (1) from its lignan aglycone bonded by an ethereal function. The key step in the synthesis involves the reaction of a benzylated alditol 4 or 5 and the unprotected 4′-demethylepipodophyllotoxin (6).     

Single-Pot Synthesis of Alkyl-Substituted Quinolines and Indoles via Photoinduced Oxidation of Primary Alcohols

Single-pot synthesis of alkyl-substituted quinolines and indoles has been performed via photoinduced oxidation of primary aliphatic alcohols (C₂–C₅) and condensation of the aldehydes (products of the alcohols oxidation) with aniline under the action of iron-containing catalysts and inorganic oxidants. The synthesis was the most efficient in the presence of FeCl₃·6H₂O as catalyst and 10% aqueous solution of NaOCl as oxidant with irradiation by Hg lamp. The synthesis mechanism through photoinduced oxidation of primary aliphatic alcohol has been suggested.     

Kristall- und MolekülStruktur von 2(C6H5)3AsO · H2SeO3

Crystal and Molecular Structure of 2(C₆H₅)₃AsO · H₂SeO₃ 2(C₆H₅)₃AsO · H₂SeO₃ crystallizes in the orthorhombic space group Fdd2—C_2v¹⁹, with a = 20.472(9), b = 32.747(1) and c = 10.008(8) Å and Z = 8; d (calc./obs.) = 1.52₇/1.52 g · cm^?3. The structure has been determined from 808 independent reflections by Patterson- and Fouriersyntheses, and has been refined by least squares methods to R = 0.056. In the compound two (C₆H₅)₃AsO-units and one selenite group are linked by short H-bonds [O …? H …? O-distance 2.48(4) resp. 2.35(4) Å]. The As? O-distances are 1.64(9), the Se? O-distances are 1.69(3), 1.83(3), resp. 1.76(3) Å.     

AB initio calculations and matrix ftir studies of the sulfur trioxide radical anion

The structures and vibrational frequencies of SO⁻₃ (C_3v) and SO⁻₂ (C_2v) have been calculated at the UHF SCF/3-21 + G¹ level. By cocondensation of Cs atoms and SO₃ in an Ar matrix the FTIR spectrum of Cs₄SO₃ has been measured. The molecule is proposed to have C_s symmetry with SO₃ binding to Cs in a bidentate fashion.     

Relation between the electrosorption of homologous phosphine oxides and their inhibitive effect on the rate of electrode reactions: Part I. Influence of dialkyl-phenyl-phosphine oxides and trialkyl-phosphine oxides on the rate of Cu(II) discharge at the mercury/solution interface

The inhibitory effect of three homologous dialkyl-phenyl-phosphine oxides (C₆H₅(R)₂) PO; R=C₂H₅, C₃H₇, C₄H₉) and trialkyl-phosphine oxides (R¹(R²)₂ PO, R¹=C₅H₁₁, C₆H₁₃; R²=CH₃, C₂H₅) on the Cu²⁺ discharge reaction, at a fully covered dropping mercury electrode has been investigated by the polarographic technique. The rate of this electrode reaction has been correlated with the film pressure π. In contrast to what was observed at the electrode covered by the film of aliphatic alcohols [18], no linear relationship between π and the logarithm of the reaction rate has been found. In fact, at low film pressures the rate depends on π, but at higher π it attains, or tends to attain, a limiting value independent of π. To explain the differences in the mechanism of Cu²⁺ discharge at the electrode surface covered by the films of aliphatic alcohols and phosphine oxides, a reaction channel in which the activated complex is created by a surface reaction between adsorbed reactant and surfactant has been considered. The equation describing the rate of a reaction following this channel has been derived. It has been shown that an equation described previously by Guidelli and Foresti [14] can be considered as a particular case of this relation.     

Untersuchungen zur reaktivität von metall-π-komplexen : XVIII. Elektrophile und nucleophile additionsreaktionen an siebenringliganden in tricarbonylmolybdän-komplexen: Synthese von [C7H9Mo(CO)3]BF4, C7H9Mo(CO)3Cl und [C7H9P(C6H5)3]BF4

C₇H₈Mo(CO)₃ reacts with HBF₄ and HCl by protonation of the ring ligand and formation of [C₇H₉Mo(CO)₃]BF₄ (I) and C₇H₉Mo(CO)₃Cl (II), respectively. The compounds are characterised by means of their IR and NMR data. The reaction of I with P(C₆H₅)₃ does not lead, as expected, to [C₇H₉Mo(CO)₃P(C₆H₅)₃]BF₄ (III) but to the phosphonium salt [C₇H₉P(C₆H₅)₃]BF₄ (IV), i.e. nucleophilic addition of the phosphine at the cycloheptadienyl group takes place. The structure of IV has been determined by ¹³C NMR measurements.     

Mass spectra of monohapto-cyclopentadienyl derivatives of group IVB elements

Dissociative ionisation of organometallic cyclopentadiene derivatives containing one, two or three M(CH₃)₃ groups (M  Si, Ge, Sn) has been studied.Among the monometallated compounds, C₅H₅Si(CH₃)₂Cl, C₅H₅Si(CH₃)₂OCH₃ and (C₅H₅)₄Sb have also been investigated. To verify fragmentation patterns, the spectra of deuterated compounds such as C₅D₅Si(CH₃)₃, C₅D₅Sn(CH₃)₃, C₅D₄Si₂(CH₃)₆ and C₅D₃Si₃)₉ have been measured. Dissociative ionisation of h¹-cyclopentadienyl derivatives has been shown to differ essentially from that of h⁵-compounds.