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  • 11
    Electronic Resource
    Electronic Resource
    Convenient Glycoside Synthesis of Amino Sugars: Michael-Type Addition to 2-Nitro-D-galactal (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 1609-1613 
    Details
    ISSN: 1434-193X
    Keywords: Glycals, nitro ; Michael additions ; Glycosylations ; Glycosides, galactosamine ; Reduction, nitro group ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Formation of 3,4,6-tri-O-benzyl-2-nitro-D-galactal (3) was readily accomplished starting from tri-O-benzyl-D-galactal (1) by acetyl nitrate addition to 2 and base-promoted acetic acid elimination. Addition of alcohols to 3 under conditions of base catalysis afforded 2-deoxy-2-nitrogalactopyranosides 4a-e in high yields; high α-selectivity was obtained with strong bases, whereas weaker bases furnished mainly the corresponding β-galactopyranosides. Chemoselective nitro group reduction in these glycosides was successfully carried out in the case of disaccharide 4cα using Raney nickel as catalyst, thereby affording after N-acetylation the corresponding 2-acetylamino-2-deoxy derivative 5cα.
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  • 12
    Electronic Resource
    Electronic Resource
    Polar and Steric Substituent Effects in 5-exo-trig Cyclizations of 1-Aryl-4-penten-1-oxyl Radicals (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 523-523 
    Details
    ISSN: 1434-193X
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -By mistake wrong concentrations were given in the footnote of Table 1 and in the Discussion. Instead of c0 = 1.2 M read c0 = 0.12 M if 2-naphthalenethiol was used as hydrogen donor and instead of c0 = 1.8 M read c0 = 0.18 M if Bu3SnH was used to trap photoproducts. In Table 2 relative rate constants of radical 2d refer to radical 2e and vice versa as correctly stated in the Discussion. In the Experimental Section (Iodocyclization) read 2.25 g (8.86 mmol) of iodine instead of 2.25 g (1.10 mmol) of iodine.
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  • 13
    Electronic Resource
    Electronic Resource
    Reactions of Dimethyl[tris(trimethylsilyl)methyl]metalanes of Aluminum and Gallium with H2S and Elemental Chalcogens - Crystal Structures of [RAl(μ-S)]2·2 THF, [RGa(μ3-S)]4, [{RAl(μ3-S)}3MeAl(μ3-S)], [RAlMe(μ-SeMe)]2, and [RGaMe(μ-TeMe)]2 [R = C(SiMe3)3] (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 2033-2039 
    Details
    ISSN: 1434-1948
    Keywords: Aluminum ; Chalcogens ; Cubanes ; Gallium ; Main group elements ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of the trialkylalane (Me3Si)3CAlMe2 × THF (1) with H2S in toluene at room temperature results in the formation of the dimeric sulfido compound [(Me3Si)3CAl(μ-S)]2 × 2 THF (3), while the reaction of the homologous gallane (Me3Si)3CGaMe2 (2) with H2S under similar conditions affords the heterocubane [(Me3Si)3CGa(μ3-S)]4 (4). Heating of compound 3 in vacuo gives a mixture of the symmetrically substituted [(Me3Si)3CAl(μ3-S)]4 (5) and the unsymmetrically substituted heterocubane [{(Me3Si)3CAl(μ3-S)}3MeAl(μ3-S)] (6). Reaction of the trialkylmetalanes 1 and 2 with elemental selenium in refluxing toluene results in the formation of the corresponding selenolates [(Me3Si)3CMMe(μ-SeMe)]2 (7, M = Al; 8, M = Ga). The compounds exhibit a high thermal stability and can not be converted to the corresponding selenides [(Me3Si)3CM(μ3-Se)]n (M = Al, Ga) upon heating. In contrast, the trialkylalane 1 does not react with tellurium metal in refluxing toluene at all, while the trialkylgallane 2 affords the tellurolate [(Me3Si)3CGaMe(μ-TeMe)]2 (9) under similar conditions. Compounds 3-9 have been characterized by 1H- and 29Si-NMR, mass, and IR spectroscopy. Furthermore, the molecular structures of compounds 3· C6H6, 4· 1.5 C6H6, 6, 7· C6H6 and 9 have been determined by X-ray crystallography.
    Additional Material: 5 Ill.
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  • 14
    Electronic Resource
    Electronic Resource
    Synthesis of D-erythro-Ceramide-1-phosphoinositol and Its Aminoglucosylated Derivative - Intermediates in GPI-Anchor Biosynthesis (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 291-298 
    Details
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Phospholipids ; Glycolipids ; Sphingosines ; Ceramides ; Ceramide-1-phosphates ; Inositols ; Glycophosphosphingolipids, synthesis ; Glycophosphoinositol anchors ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The readily available 2,3:4,5-di-O-cyclohexylidene-D-myo-inositol derivative 3 was converted into the 1-O-unprotected D-myo-inositol derivative 6. Reaction with the phosphite derivative 7 of 3-O-tert-butyldimethylsilyl-protected ceramide furnished the target molecule D-erythro-ceramide-1-phosphoinositol (1). Reaction of O-(3,4,6-tri-O-acetyl-2-azido-β-D-glucopyranosyl)trichloroacetimidate (20) with 3 gave exclusively α(1→6)-connected glycoside 21 which was converted into the 1α-O-unprotected derivative 24. Reaction with the D-erythro-azidophytosphingosine-derived ceramide-1-phosphite derivative 17 led, after oxidation and removal of the cyanoethyl group, to protected 2-azido-D-glucopyranosyl-α(1→6)-D-myo-inositol-1-phospho-ceramide (25) which could be fully deprotected in two steps to afford the target molecule, the ceramide derivative of 2-amino-2-deoxy-D-glucopyranosyl-α(1→6)-D-myo-inositol-1-phosphate (2).
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  • 15
    Electronic Resource
    Electronic Resource
    C-Glycosides of Visnagin Analogues (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2317-2322 
    Details
    ISSN: 1434-193X
    Keywords: C-Glycosyl compounds ; Flavones ; Flavanones ; O-Glycosyl trichloroacetimidates ; Fries rearrangement ; Carbohydrates ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Glycosylation of the visnagin cleavage product 2 with O-acetyl-protected glycosyl donor 5a afforded O-glycoside 6a, which could be transformed into the O-benzyl-protected compound 6b. The latter underwent Fries-type rearrangement to afford C-glycoside 4b. The same product could be obtained directly from 2 and O-benzyl-protected glycosyl donor 5b. Reaction of 4b with benzaldehyde and anisaldehyde furnished chalcones 7A,B, which, upon treatment with base, furnished flavanone C-glycosides 10A,B. Selenium dioxide oxidation of 10A,B or of 7A,B led to the corresponding flavone C-glycosides 11A,B. The same result was obtained by Baker-Venkataraman rearrangement; on treatment with base, the O-aroyl compounds 12A-C gave C-aroyl compounds 13A-C, which, on addition of TMSOTf, furnished flavone C-glycosides 11A-C. Hydrogenolytic O-debenzylation of 11A afforded target molecule 3A, which was transformed into O-acetyl derivative 14A for characterization. Structural assignments of all compounds were based on 1H-NMR data.
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  • 16
    Electronic Resource
    Electronic Resource
    Glycosyl Phosphatidylinositol (GPI) Anchor Synthesis Based on Versatile Building Blocks - Total Synthesis of a GPI Anchor of Yeast (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1153-1165 
    Details
    ISSN: 1434-193X
    Keywords: Carbohydrates ; Phospholipids ; Glycolipids ; Sphingosines ; Ceramides ; Ceramides-1-phosphates ; Glycosylation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -For the design of a synthesis of target molecule 1 the retrosynthetic analysis yielded building blocks 2-5, of which ceramide 2-phosphite derivative 2 and aminoethyl phosphite derivative 5 are known. The generation of α-glucosaminyl (1→6)inositol building block 3 was based on pseudodisaccharide 6 which was selectively benzoylated at 6b-O and then selectively benzylated at 3b-O to give 3. The synthesis of tetramannosyl building block 4 started from known ortho ester derivative 8 which was transformed into versatile mannosyl donors 13 and 18 and into acceptor 22. Reaction of 13 with 22 gave α-disaccharide 23, deacetylation and then mannosylation with 18 gave trisaccharide 25; ensuing deacetylation and mannosylation with 13 gave tetrasaccharide 27; deallylation, acetylation, regioselective removal of the anomeric O-acetyl group and treatment with CCl3CN/DBU afforded 4. Glycosylation of 3 with donor 4 led to pseudohexasaccharide 31 in high yield. Replacement of the O-acyl groups by O-benzyl groups and then exchange of the menthyloxycarbonyl group by an O-acetyl group gave 36 which enabled regioselective attachment of 2 and 5. To this end, the 6e-O-silyl group was removed and then the aminoethyl phosphate residue was attached with reagent 5 to give 38 in high yield. 1a-O-Deacetylation and then reaction with 2 afforded 40 as fully protected 1 which was liberated in two steps; treatment with acid removed all acid labile protective groups and finally catalytic hydrogenation afforded the desired GPI anchor 1 which could be fully structurally assigned.
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  • 17
    Electronic Resource
    Electronic Resource
    The Aluminum-Nitrogen Bond in Monomeric Bis(amino)alanes: A Systematic Experimental Study of Bis(tetramethylpiperidino)alanes and Quantum Mechanical Calculations on the Model System (H2N)2AlY (1998)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1998 (1998), S. 1095-1114 
    Details
    ISSN: 1434-1948
    Keywords: Aminoalanes ; Alanes ; Ab initio calculations ; 27Al-NMR spectroscopy ; Structure elucidation ; Substituent effects ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reactions of metallated nucleophiles MIY [Y = OR, SR, NR2, PR2, AsR2, CR3, Si(SiMe3)3, R = organyl, H] with bis(2,2,6,6-tetramethylpiperidino)aluminum halides [tmp2AlX, (X = Cl, Br, I)] offer facile access to a variety of bis(amino)alanes of the type tmp2AlY. As indicated by 27Al-NMR spectroscopy, mass spectrometry and X-ray crystal structure determina-tions, all of these compounds are monomeric in the solid state, in solution, and in the gas phase. Even Al-E single bonds (E = Si, P, As etc.) that are not commonly encountered are stabilized by the supporting tmp fragments. The results of a systematic analysis of the bonding parameters determined for the tmp2AlY compounds, combined with a quantum mechanical study on model compounds (H2N)2AlY, not only reveal the presence of a highly polar Al-N bond, but at the same time rule out AlN-pp(π) bonding, in contrast to the situation in the analogous tmp2BY compounds. It is shown that the Al-N bond length depends on the acidic character of the protic species HY: the shorter d(Al-N), the less basic is Y.
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  • 18
    Electronic Resource
    Electronic Resource
    Preparation and Structural Investigations of (dippNSiMe3Si)2(Cp*Ti)2(NH)6 (dipp = 2,6-iPr2C6H3), [dippNSiMe3Si(NH2)NH]3 and [dippNSiMe3Ge(NH2)NH]3 (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 863-867 
    Details
    ISSN: 1434-1948
    Keywords: Germanium ; Nitrogen ; Silicon ; Titanium ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reaction of dippNSiMe3Si(NH2)3 (1) (dipp = 2,6-iPr2C6H3) with Cp*TiMe3 (Cp* = C5Me5) and Me3SnCl yields the new heterocyclic adamantane (dippNSiMe3Si)2(Cp*Ti)2(NH)6 (2) containing the Si2Ti2(NH)6 core and the silicon-nitrogen six-membered ring compound [dippNSiMe3Si(NH2)NH]3 (4). [dippNSiMe3Ge(NH2)2]2NH (5) reacts with AlMe3 to give the germanium-nitrogen six-membered ring compound [dippNSiMe3Ge(NH2)NH]3 (6). The compounds 2, 4 and 6 have been structurally characterized by single-crystal X-ray structural analysis.
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  • 19
    Electronic Resource
    Electronic Resource
    Synthesis of (RSn)4X6 Adamantanes (X = O, S, Se) in Liquid Ammonia and in the Two-Phase System Liquid Ammonia/THF (1999)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 1999 (1999), S. 869-872 
    Details
    ISSN: 1434-1948
    Keywords: Adamantane ; Liquid ammonia ; Oxygen ; Sulfur and selenium ; Tin ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactions of trisSnBr3 (1) [tris = (Me3Si)3C] and nBuSnCl3 with Na2X (X = O, S, Se) yield the heterocyclic adamantanes 2-6. The reaction of 1 with Na2O is carried out in liquid ammonia under normal pressure at -78 °C to give (trisSn)4O6 (2). However, the reaction of 1 with Na2S and Na2Se under pressure at room temperature results in the formation of (trisSn)4S6 (3) and (trisSn)4Se6 (4). nBuSnCl3 reacts with Na2S and Na2Se in liquid ammonia at -33 °C under normal pressure to give (nBuSn)4S6 (5) and (nBuSn)4Se6 (6), respectively.
    Additional Material: 2 Ill.
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  • 20
    Electronic Resource
    Electronic Resource
    C-Disaccharides of Ketoses (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 502-510 
    Details
    ISSN: 0947-6539
    Keywords: alkynes ; C-glycosides ; cobalt complexes ; cyclizations ; enzyme inhibitors ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Reaction of gluconolactone 2 with allylmagnesium bromide at low temperatures afforded ketopyranose 3, which could easily be converted into open-chain ketoses (R)-6 and (S)-6. Their reaction with lithioacetylide 9 afforded propargylic alcohol derivatives (R)-10 and (S)-10, which could not be cyclized directly to the desired C-ketosides. They were converted by standard procedures into (R)-14 and (S)-14 and then into dicobalthexacarbonyl complexes (R)-16 and (S)-16. A facile acid-catalyzed ring closure gave the desired C-ketosides (R)-18 α/β and (S)-18α/β, respectively, in different ratios. In order to demonstrate that removal of the protective groups and hydrogenation of the CC triple bond proceed smoothly, (R)-18 α was transformed into the deprotected target molecule (R)-1 α. For the assignment of the new chiral centers at C-2/2′ and at C-8, (S)-18α was transformed into azido derivative (S)-22α, which underwent intramolecular cycloaddition to afford the spiro derivative (S)-25α. Because of the conformational constraints in this molecule, unequivocal configurational assignment was possible with the help of NMR data.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020508
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