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  • Organic Chemistry  (7)
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  • 1
    Electronic Resource
    Electronic Resource
    Models for the Active Center of Pterin-Containing Molybdenum Enzymes: Crystal structure of a molybdenum complex with sulfur and pterin ligands (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 103-110 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The first crystal structure of a molybdenum complex 9 with a hydrogenated pterin and a sulfur ligand contributes to the discussion about the active center of molybdenum and tungsten enzymes containing a molybdopterin cofactor. Complex 9 was synthesized through a redox reaction of [MoVIO2 (LN-S2)] (8; LN-S2 = pyridine-2, 6-bis(methanethiolato)) with 5, 6, 7, 8-tetrahydropterin (7). 2 HCl (H4Ptr.2 HCl). The complex crystallizes, with a non-coordinating Cl-atom acting as a counterion, in the monoclinic space group C2/c (No. 15) with cell dimensions a = 22.900(5), b = 10.716(2), c = 17.551(4) Å, β = 120.36(3)°, and Z = 8. We interpret 9 as [MoIVO(LN-S2)(H+-q-H2Ptr)]Cl (q = quinonoid; H2Ptr = dihydropterin), i.e., a MoIV monooxo center coordinated by a pyridine-2, 6-bis(methanethiolato) ligand and a protonated dihydropterin. The spectroscopic properties of this new complex are comparable to those of other crystalline molybdenum complexes of hydrogenated pterins without additional S-coordination. The slightly H2O-soluble complex 9 reacts with the natural enzyme substrate DMSO very slowly, possibly due to the lack of easily dissociable ligands at the metal center.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800110
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  • 2
    Electronic Resource
    Electronic Resource
    Light-induced Dehydrodimerization of 3-Hydroxypyrroles (1984)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 67 (1984), S. 1957-1962 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Irradiation (λ 〉 280 nm) of 3-hydroxy-1H-pyrrole-2-carboxylates 1 in CH3CN gives the [2.2′-bi(3-oxo-2,3-dihydro-1H-pyrrole)]-2-,2′-dicarboxylates 2 in reasonable to good yields. The corresponding N-methylpyrroles 3 only undergo slow photodecomposition under similar conditions. Several 2-methyl-3-oxo-2,3-dihydro-1H-pyrrole-2-carboxylates 4 and 5 were synthesized to compare their spectral data with those of the dehydrodimers 2. A X-ray structure analysis was performed for diethyl [2,2′-bi(4,5-dimethyl-3-oxo-2,3-dihydro-1 H-pyrrole)]-2,2′-dicarboxylate (2b). The originally proposed [3,3′-bi(3H-pyroole)] structure for compounds 2a-e proves incorrect.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19840670734
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  • 3
    Electronic Resource
    Electronic Resource
    Preparation, Characterisation, and Structure of N-Methylated Derivatives of 1,3,5-Triamino-1,3,5-trideoxy-cis-inositol: Polyalcohols with Unusual Acidity (1990)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 73 (1990), S. 97-105 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 1,3,5-Trideoxy-1,3,5-tris(dimethylamino)-cis-inositol (TDCI) and 1,3,5-trideoxy-1,3,5-tris(trimethylammonio)-cis-inositol (TTCI) were prepared by methylation of 1,3,5-triamino-1,3,5-trideoxy-cis-inositol (TACI). The ability of TDCI to form both intermolecular and intramolecular H-bonds, as demonstrated by X-ray diffraction, is probably responsible for the good solubility of TDCI in almost every common solvent. TTCI was found to be a polyol of unusual high acidity (pK1 = 8.14 ± 0.02, pK2 = 13.0 ± 0.2). This phenomenon could be explained by electrostatic interactions between the charged substituents of the cyclohexane residue.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19900730110
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  • 4
    Electronic Resource
    Electronic Resource
    Konfiguration von 2-Amino-4-hydroxy-4-(5-hydroxy-2-pyridyl)-3-methylbuttersäure, der N-terminalen Aminosäure der Nikkomycine (1980)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1980 (1980), S. 1728-1735 
    Details
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Configuration of 2-Amino-4-hydroxy-4-(5-hydroxy-2-pyridyl)-3-methylbutyric Acid, the N-Terminal Amino Acid of the NikkomycinsThe N-ethylthio(thiocarbonyl)derivative 2 of the N-terminal amino acid 1 of the nikkomycin antibiotics shows a positive Cotton effect in its circular dichroism spectrum and therefore 1 is assigned to the L-series. The relative configuration of the C atoms 3 and 4 was ascertained by 1H-NMR investigations and crystal structure analysis. Accordingly, 1 is assigned the configuration 2S,3S,4S.
    Notes: Das N-Ethylthio(thiocarbonyl)derivat 2 der N-terminalen Aminosäure 1 der Nikkomycin-Antibiotika weist Circulardichroismus mit positivem Cottoneffekt auf und 1 ist daher der L-Reihe zu-zuordnen. Die relative Konfiguration an den C-Atomen 3 und 4 wurde durch 1H-NMR- und Kristallstrukturuntersuchungen bestimmt. Danach hat 1 die Konfiguration 2S,3S,4S.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.198019801112
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  • 5
    Electronic Resource
    Electronic Resource
    Synthese reiner Stereoisomerer der N-terminalen Aminosäure von Nikkomycin B (1985)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1985 (1985), S. 2165-2177 
    Details
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Synthesis of Pure Stereoisomers of the N-terminal Amino Acid of Nikkomycin BPure stereoisomers of 2-amino-4-hydroxy-4-(p-hydroxyphenyl)-3-methylbutanoic acid (8c), the N-terminal amino acid of nikkomycin B (10a, b), were synthesized by 1,3-dipolar cycloaddition of (ethoxycarbonyl)methanenitrile oxide (2) to the olefines 1, separation of the diastereomeric 4,5-dihydro-3-isoxazolecarboxamides 6, and diastereoselective reductive cleavage and hydrolysis of 6. X-ray structure analysis revealed the absolute configuration (2R,3R,4R) for one pure synthetic stereoisomer of 8c. Gas chromatography on a chiral stationary phase and 1H NMR enabled us to assign the (2S,3S,4S) configuration to the natural amino acid.
    Notes: Reine Stereoisomere von 2-Amino-4-hydroxy-4-(p-hydroxyphenyl)-3-methylbuttersäure (8c), der N-terminalen Aminosäure von Nikkomycin B (10a, b), wurden nach 1,3-dipolarer Cycloaddition von (Ethoxycarbonyl)methannitriloxid (2) an die Olefine 1 und Trennung der diastereomeren 4,5-Dihydro-3-isoxazolcarboxamide 6 durch diastereoselektive reduktive Spaltung und Verseifung von 6 hergestellt. Mit Hilfe eines reinen, synthetischen Stereoisomers von 8c, dessen absolute Konfiguration (2R,3R,4R) durch Kristallstrukturanalyse bestimmt werden konnte, sowie mit Hilfe von Gaschromatographie an chiraler Phase und 1H-NMR gelang es, der natürlichen Aminosäure die Konfiguration (2S,3S,4S) zuzuordnen.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.198519851107
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  • 6
    Electronic Resource
    Electronic Resource
    Untersuchungen zur Konfiguration und Konformation der Nucleosidbausteine der Nikkomycine (1984)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1984 (1984), S. 1216-1229 
    Details
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Investigations on the Configuration and Conformation of the Nucleoside Residues of the NikkomycinsThe configuration of 5′-amino-5′-deoxy-β-D-allofuranuronosyl derivatives of uracil and 4-formyl-4-imidazolin-2-one could be assigned to the C-terminal nucleoside residues 1 and 2, respectively, of the nikkomycins, according to 1H NMR spectroscopy, circular dichroism, and X-ray analysis. The latter method also showed that 1 and 2 have C-2′-endo-C-1′-exo conformation (21T) with gauche (g+) position of hte CO⊖2-group, trans (t) position of the NH⊕3-group, and anti position of the base. The conformation in solution was determined by 1H NMR spectra and from the 13C-1-H-vicinal couplings and shows only minor deviations from the conformation of the crystal.
    Notes: Den in den Nikkomycinen C-terminal gebundenen Nucleosiden 1 und 2 konnte durch 1H-NMR-Spektroskopie, Circulardichroismus und Kristallstrukturanalyse die Konfiguration von 5′-Amino-5′-desoxy-β-D-allofuranuronosyl-Derivaten des Uracils bzw. 4-Formyl 4 imidazolin-2-ons zugeordnet werden. Die Kristallstrukturanalyse zeigte darüber hinaus, daß 1 und 2 in der C-2′-endo-C-1′-exo-Konformation (21T) vorliegen, wobei die CO⊖2-Gruppe die gauche-Lage (g+), die NH⊕3-Gruppe die trans-Lage (t) und die Base anti-Stellung einnehmen. Die Konformation in Lösung wurde aus 1H-NMR-Spektren und durch Bestimmung der 13C-1H-Vicinalkopplungen ermittelt und weicht nur geringfügig von der Konformation im Kristall ab.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.198419840617
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  • 7
    Electronic Resource
    Electronic Resource
    Synthetic Anthracyclinones, XXIX. Quinone Antibiotics with Five Substituents at the Hydroaromatic Ring (1985)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1985 (1985), S. 1311-1328 
    Details
    ISSN: 0170-2041
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Synthetische Anthracyclinone, XXIX.- Chinon-Antibiotica mit fünf Substituenten am hydroaromatischen RingDas aus Naphthazarin (6) und dem Dien 7 erhältliche Addukt 8 wird zu 15 epoxidiert und durch Basenbehandlung zum Olefin 25 umgesetzt. Der durch Spaltung des Silylethers 25 erhältliche Allylalkohol 26 wird zu 28 und 30 epoxidiert und mit Methanol zu den Methylethern 32 und 33 geöffnet. Die relative Konfiguration des aus 33 erhältlichen Acetonids 36 wird durch Röntgenstrukturanalyse abgesichert; damit ist auch die relative Konfiguration 1 a des Altersolanols A bewiesen. Ferner bestätigen massenspektrometrische Untersuchungen die Stereochemie der Isomeren 31- 33. Die tetracyclischen Anthracyclinone 40- 42 werden durch Diels-Alder-Reaktion von 31, 33 und 36 mit 1-Methoxy-1, 3-butadien erhalten.
    Notes: From the adduct 8, obtained from naphthazarin (6) and the diene 7, the olefin 25 is synthesized via epoxidation (→ 15) and treatment with base. Cleavage of the silyl ethers 25 yields the allylic alcohol 26 which can be epoxidized to give 28 and 30 and subsequently cleaved with methanol to yield the methyl ethers 32 and 33. The relative configuration of the acetonide 36 obtained from 33 is confirmed by X-ray analysis; consequently, the relative configuration 1 a of altersolanol A is proved. Furthermore, the mass spectrometrical investigations support the stereochemistry of the isomers 31- 33. The tetracyclic anthracyclinones 40- 42 are synthesized by Diels-Alder reaction of 31, 33, and 36 with 1-methoxy-1, 3-butadiene.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.198519850703
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