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  • 1
    Electronic Resource
    Electronic Resource
    Synthesis of Lacto-N-neohexaose and Lacto-N-neooctaose Using the Dimethylmaleoyl Moiety as an Amino Protective Group (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 319-326 
    Details
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Amino sugars ; Protecting groups ; Glycosylations ; Trichloroacetimidates ; Oligosaccharides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The N-DMM-Protected lactosamine derivative 2 was readily transformed into the corresponding glycosyl donor 4 and into acceptor 5. A TMSOTf-catalyzed glycosidation afforded the derived tetrasaccharide 6 which led to glycosyl donor 9. Reaction of 9 with lactose derivative 10 as acceptor gave the desired hexasaccharide 11. Cleavage of all protective groups and N-acetylation afforded the target molecule 1b (lacto-N-neohexaose). Glycosylation of acceptor 10 with donor 4 furnished tetrasaccharide 16 which, employing standard procedures, gave acceptor 18. Glycosylation of 18 with donor 9 furnished, under standard conditions, octasaccharide 19. Cleavage of all protective groups and N-acetylation afforded the target molecule 1c (lacto-N-neooctaose). Both 1b and 1c were obtained in good overall yields.
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  • 2
    Electronic Resource
    Electronic Resource
    Nickel- and Palladium-Catalyzed Cross-Coupling Reactions at the Bridgehead of Bicyclo[1.1.1]pentane Derivatives - A Convenient Access to Liquid Crystalline Compounds Containing Bicyclo[1.1.1]pentane Moieties (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1137-1155 
    Details
    ISSN: 1434-193X
    Keywords: Bicyclo[1.1.1]pentane ; Haloarenes, cross-coupling of ; Propellanes ; Palladium ; Catalysis ; Small-ring systems ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Radical addition reactions of organyl iodides 7a-s onto [1.1.1]propellane (2) followed by halogen-lithium exchange and transmetallation with zinc chloride, as well as additions of Grignard reagents to 2, have furnished a variety of 3-substituted bicyclo[1.1.1]pentyl-1-magnesium (14) and -zinc (19) derivatives. The latter have been coupled with various alkenyl, aryl, and biaryl halides and triflates under NiCl2dppe, Pd(PPh3)4, or PdCl2(dppf) catalysis to give a number of 1,3-disubstituted bicyclo[1.1.1]pentyl derivatives 17, 20, and 23, several of which exhibit liquid crystalline properties, in moderate to very good yields. The coupling products 20ca, 23ab, 23ae, 23ff, and 23fg have been further transformed to yield bicyclo[1.1.1]pentyl derivatives 32, 24ab, 24ae, 27ff, and 27fg, respectively, bearing alkynyl, cyano, and/or alkenyl groups.
    Additional Material: 7 Tab.
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  • 3
    Electronic Resource
    Electronic Resource
    Synthesis of 15N-Labelled D-Isovaline and α-Aminoisobutyric Acid (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 857-859 
    Details
    ISSN: 1434-193X
    Keywords: α,α-Dialkylated amino acids ; Isotopic labeling ; Strecker synthesis ; Solvent effects ; Stereoselective hydrolysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---[15N]-D-isovaline was prepared from DL-[α-15N]-α-aminoisovaleramide by enzymatic resolution with Mycobacterium neoaurum. The 15N-isotope was introduced during the Strecker synthesis of its precursor, e.g. aminoisovaleronitrile. Attempts to prepare the amino nitrile precursor of [15N]-α-aminoisobutyric acid (Aib) led to a poor yield and loss of the label. Significantly, improved results were obtained when a cosolvent is present during formation of aminoisobutyronitrile.
    Additional Material: 1 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    An SiO2-Embedded Nanoscopic Pd/Au Alloy Colloid (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 819-822 
    Details
    ISSN: 1434-1948
    Keywords: Colloids ; Sol-gel processes ; Immobilization ; Heterogeneous catalysts ; Hydrogenations ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A bimetallic, fully alloyed Pd/Au colloid of 3.0 nm particle size, obtained by the co-reduction of Pd and Au salts with tetraalkylammonium triethylhydroborate, was embedded in a silica matrix employing a modified sol-gel procedure with THF as the solvent. The removal of the protecting tenside led to a mesoporous texture with a comparatively narrow pore distribution. The physical characterisation by a combination of several techniques has shown that the SiO2-embedded Pd/Au colloid preserves the size and the structural characteristics of the colloidal metal precursor. The new material exhibits catalytic properties in selective hydrogenation.
    Additional Material: 4 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Enantiopure Dendrimers Derived from the 1,1′-Binaphthyl Moiety: A Correlation Between Chiroptical Properties and Conformation of the 1,1′-Binaphthyl Template (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 61-71 
    Details
    ISSN: 1434-193X
    Keywords: Binaphthyls ; Chirality ; Circular dichroism ; Dendrimers ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The absorption and CD spectra of a series of Fréchet (compounds 7-10) and backfolding (compounds 11-12) dendrimers derived from enantiopure (S)-2,2′-dihydroxy-1,1′-binaphthalene have been recorded (THF) in the range 200-350 nm. All the compounds examined show a positive couplet between 200 and 240 nm (1B transition of the 2-naphthol chromophore), the intensity of which (Δεmax of the low-energy branch) ranges between 100 and 40. By means of the DeVoe polarizability model the intensity of the 1B couplet has been calculated vs. the dihedral angle θ. This analysis provides θ angles of 95-110° for the Fréchet dendrimers and 100-110° for the backfolding compounds. These values clearly indicate that the torsional angle θ, defined by the two naphthalene planes, never exceeds the critical value of 110°. This investigation confirms the wide utility of CD spectroscopy to provide geometrical information that cannot be obtained by other types of structural analysis.
    Additional Material: 5 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    “Crowned” Fe4S4 Clusters as Electrochemical Metal Ion Sensors (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 253-264 
    Details
    ISSN: 1434-1948
    Keywords: Iron-sulfur clusters ; Crown ethers ; Electrochemical devices ; Host-guest chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of Fe4S4 cluster compounds, I, III, and V, in which the cuboidal cluster core is appended with four crown ether thiolate ligands, and II and IV, bearing thiolate ligands without crown ether parts, has been synthesized and characterized. The spectroscopic and electrochemical properties of these compounds are determined by the electronic nature of the thiolate ligands. Only in the case of III, where a very short α-thioacetyl linker was used to connect the crown ether ligands to the cluster core, was a restricted conformational freedom of the ligand observed. A detailed electrochemical study of the influence of alkali and earth alkali metal ions (Li+, Na+, K+, Mg2+, and Ba2+) on the reversible 2-/3- reduction of the cluster compounds was performed. In the case of the crown ether appended clusters I, III, and V, the addition of these metal ions resulted in an anodic shift, i.e. in positive direction, of the reduction potential (modulation effect) and to larger current responses (promotion effect). The magnitude of the modulation effects is determined by the binding affinity of the metal ions in the crown ether ligands, and by the distance between bound metal ions and the redox active cluster core. Variation of the linker between the cluster core and the metal ion binding site resulted in cluster compounds with almost inverse selectivities for e.g. K+ and Ba2+ in the case of I and III. For the large effects found for compound I a lariat binding mode is proposed.
    Additional Material: 6 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    [Hg7As4I3](SnI3): Trapping the SnI31- Anion in the Cavities of the Unprecedented Mercury-Arsenic-Iodine Network (2000)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 2000 (2000), S. 265-270 
    Details
    ISSN: 1434-1948
    Keywords: Host-guest compounds ; Tin ; Mercury ; Pnictide halides ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A novel host-guest compound [Hg7As4I3](SnI3) has been prepared by a standard ampoule technique and its crystal structure was determined. It crystallizes in a cubic system [space group P213, a = 13.110(1) Å, Z = 4] with a unique structure type. The crystal structure comprises two parts: the three-dimensional [Hg7As4I3]1+ host network, and the SnI31- guest anions encapsulated in the cavities of the network. The network is built from the As2Hg7 bitetrahedra and As2Hg6 octahedra, which share corners, and contains an additional iodine atom connected to one of the mercury vertices. The SnI31- anion has the shape of a pyramid with the tin atom in a vertex. According to the quantum-chemistry calculations, the geometry of the anion deviates substantially from the equilibrium one, and is influenced by the distant mercury atoms of the host network.
    Additional Material: 6 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Hydrolytic Reactions of the cis-Methyl Ester of 3′-Deoxy-3′-thiothymidine 3′,5′-Cyclic(phosphorothiolate) (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1987-1991 
    Details
    ISSN: 1434-193X
    Keywords: Nucleotides ; Thiophosphates ; Hydrolyses ; Reaction mechanisms ; Kinetics ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hydrolysis of the cis-methyl ester of 3′-deoxy-3′-thiothymidine 3′-S,5′-O-cyclic(phosphorothiolate) (1a) has been followed by HPLC and MS. At pH 〈 2 hydrolysis of the thiophosphate triester moiety is acid-catalyzed (first order), while between pH = 2 and 5 the reaction is pH-independent and at pH 〉 5 first order in hydroxide ion. The uncatalyzed and acid-catalyzed reactions yield two thiophosphate diesters, the 3′-S,5′-O-cyclic phosphorothiolate 2 and 3′-S-phosphorothiolate methyl ester 3, in a 9:1 and 1:3 molar ratio, respectively. The hydroxide ion catalyzed reaction gives the endocyclic P-O and P-S bond-cleavage products (3 and 4, respectively) in a 1:2 molar ratio. The pH-independent reaction is suggested to take place by attack of a water molecule on the carbon atom and concomitant C-O bond rupture, whereas the alkaline and acidic reactions involve attack of the nucleophile on the phosphorus atom and formation of a pseudorotating thiophosphorane intermediate. Under acidic conditions, cleavage of the N-glycosidic linkage competes with the phosphoester hydrolysis, corresponding to 20% of the hydrolysis products at pH 〈 1.
    Additional Material: 2 Tab.
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  • 9
    Electronic Resource
    Electronic Resource
    Near-Infrared and Visible Luminescence from Terphenyl-Based Lanthanide(III) Complexes Bearing Amido and Sulfonamido Pendant Arms (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1923-1931 
    Details
    ISSN: 1434-193X
    Keywords: Lanthanides ; Polydentate ligands ; Luminescence spectroscopy ; Near-infrared luminescence ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A series of m-terphenyl-based ligands bearing three coordinating oxyacetate and two amido or two sulfonamido groups, (1a-b)H3 and (2)H3, respectively, have been synthesized and characterized. The structures of the corresponding neutral complexes have been studied using 1H-NMR spectroscopy and luminescence experiments. The photophysical properties of the (1a-b)Eu, (2)Eu, (1a)Tb, and (2)Tb complexes have been studied to determine the structure of the first coordination sphere in methanol. The first coordination sphere consists of eight donor atoms provided by the ligand (three chelating oxyacetate groups and two amide or sulfonamide oxygens), and one methanol molecule. The (1a)Dy and (1a)Sm complexes exhibited sensitized luminescence in the visible spectral region, but the luminescence intensity was very sensitive to quenching by C-H groups. The near-infrared emitting (1a)Ln and (2)Ln complexes exhibited sensitized luminescence at wavelengths (at 880, 1060, and 1330 nm for Nd3+, at 980 nm for Yb3+, and at 1550 nm for Er3+) of interest for applications in optical telecommunication devices. The luminescence lifetimes of these complexes in DMSO and [D6]DMSO are in the range of microseconds. The luminescent state of the NIR emitting lanthanide ions is very efficiently quenched by high frequency oscillators (such as C-H groups) in the solvent and the ligand.Supporting information for this article is available on the WWW under //http://www.wiley-vch.de/contents/jc_2046/2000/99457_s.pdf or from the author.
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