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  • Articles  (75)
  • Organic Chemistry  (51)
  • Aircraft Stability and Control
  • GENERAL
  • Inorganic Chemistry
  • 1990-1994  (54)
  • 1960-1964  (21)
  • 1955-1959
  • 1993  (54)
  • 1961  (21)
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  • 1990-1994  (54)
  • 1960-1964  (21)
  • 1955-1959
Year
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  • 1
    Electronic Resource
    Electronic Resource
    Muricatetrocins A and B and Gigantetrocin B: Three New Cytotoxic Monotetrahydrofuran-Ring Acetogenins from Annona muricata (1993)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 76 (1993), S. 2433-2444 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Extracts from the seeds of Annona muricata yielded three new Annonaceous acetogenins: muricatetrocin A (= (5S)-3-{(2R)-2-hydroxy-9-{(2R,5S)-tetrahydro-5-[(1S,4S,5S)-1,4,5-trihydroxyheptadecyl]furan-2-yl}nonyl}-5-methylfuran-2(5H)-one; 1), muricatetrocin B (= (5S)-{(2R)-2-hydroxy-9-{(2S,5S)-tetrahydro-5-[(1S,4S,5S)-1,4,5-trihydroxyheptadecyl]furan-2-yl}nonyl}-5-methylfuran-2(5H)-one; 2), and gigantetrocin B (= (5S)-3-{(2R)-2-hydroxy-7-{(2S,5S)-tetrahydro-5-[(1S,4R,5R)-1,4,5-trihydroxynonadecyl]furan-2-yl}heptyl}-5-methyl-furan-2(5H)-one; 3). Their C-skeletons were deduced by mass spectrometry. Configurations were determined by 1H-NMR of ketal derivatives and 2D-NMR experiments utilizing Mosher esters. A previously described compound, gigantetrocin A (= (5S)-3-{(2R)-2-hydroxy-7-{(2S,5S)-tetrahydro-5-[(1S,4S,5S)-1,4,5-trihydroxynonadecyl]furan-2-yl}heptyl}-5-methylfuran-2-(5H)one; 4), was also isolated and is new to this species. Compounds 1-4 were all selectively cytotoxic for the HT-29 human colon-tumor cell line with potencies at least 10 times that of adriamycin.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19930760703
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  • 2
    Electronic Resource
    Electronic Resource
    Homoaromaticity of decamethyl[5]pericyclyne (1993)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 6 (1993), S. 316-318 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: It is shown that a theoretical computation of the Dewar resonance energy of decamethyl [5] pericyclyne should give the same value for the homoaromaticity of this compound as that calculated earlier from heat of hydrogenation measurements. Both methods show this quantity to be small, but the accuracy of the methods appears insufficient for more exact agreement.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610060510
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  • 3
    Electronic Resource
    Electronic Resource
    3-Methylcarboxy-1H-indazole. Theoretical study of its formation via intramolecular aliphatic diazonium coupling and x-ray crystal structure (1993)
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 6 (1993), S. 201-214 
    Details
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The methyl ester of 1H-indazole-3-carboxylic acid (2-Me) is formed in the diazotization of o-aminophenylacetic acid to o-diazoniumphenylacetic acid (1) in an intramolecular aliphatic diazonium coupling. 2-Me was identified and characterized by single-crystal x-ray diffraction and found to crystallize as hydrogen-bonded trimers of crystallographically independent molecules. The methylcarboxy groups are rotated slightly out of the best plane of the trimer resulting in only a pseudo-threefold axis. The crystal structure of 2-Me is compared with other indazoles and pyrazole. Regioselective electrophilic diazonium ion addition to the enol tautomer of 1 and subsequent hyrazone-azo tautomerization are proposed as a possible mechanism for indazole formation under acidic conditions. The tautomerization equilibrium between acetic acid and its enol 1,2-dihydroxyethene was studied and the effects of phenyl and o-diazoniumphenyl substitution on this equilibrium were explored with semi-empirical quantum mechanical methods. The performance of the semi-empirical method was assessed by comparison with ab initio and/or experimental data. It was found that the enol of o-diazoniumphenylacetic acid is stabilized greatly owing to extended conjugation and push-pull interactions in the enol form. These results suggest that the enol tautomer might be a viable reactive intermediate that warrants considerations in discussions of reaction mechanisms.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/poc.610060403
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  • 4
    Electronic Resource
    Electronic Resource
    Ethylation of methylarsenic(III) compounds by sodium tetraethylborate (1993)
    New York, NY [u.a.] : Wiley-Blackwell
    Applied Organometallic Chemistry 7 (1993), S. 577-581 
    Details
    ISSN: 0268-2605
    Keywords: Organoarsenic ; sodium tetraethylborate ; gas chromatography-atomic absorption spectrometry ; cold trap-atomic absorption spectrometry ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The compounds MeAsBr2 and Me2AsBr at concentrations of (1-5) × 10-3 M in acetone solution are ethylated in high yield by NaBEt4 to MeEt2As and Me2EtAs, as shown by 1H NMR spectroscopy. The extents of ethylation of MeAs2+ and Me2As+ (expressed as ions, by convention) in aqueous acid solutions [at concentrations of (5-20) × 10-6 M] were investigated using cold trap/AA and GC AA procedures. The species Me2As+ was ethylated (to give Me2EtAs) in good yield (88%); in contrast, MeAs2+ produced the volatile trialkylarsine, MeEt2As, in poor yield (30%). No volatile trialkylarsine could be obtained on treating inorganic arsenic(III) (As3+) solutions with NaBEt4.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aoc.590070718
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  • 5
    Electronic Resource
    Electronic Resource
    Konstitution und Eigenschaften des Biphenylen-(4.4′)-bis-[methyl-atropiniumbromids], einer biquartären Atropinverbindung (1961)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 94 (1961), S. 38-42 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Bei der Herstellung von p-Biphenylyl-methyl-atropiniumbromid wurde als Nebenprodukt ein neues, hochtoxisches, biquartäres Atropinderivat isoliert und die Konstitution bewiesen.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19610940106
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  • 6
    Electronic Resource
    Electronic Resource
    Internal Nucleophilic Termination in Acid-Mediated Polyene Cyclisations: Synthetic access to methyle homologs of (±)-Ambrox® and its diastereoisomers (1993)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 76 (1993), S. 1608-1618 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Treatment of ten monocyclic dienols 8-11 with an excess of fluorosulfonic acid in 2-nitropropane at -90° afforded diastereoisomeric mixtures of racemic tricyclic ethers 12-14 in 81-91% yield (see tables 1 and 2). These transformations represent further examples of biomimetic acid-mediated cyclisations in which an OH group serves as the internal nucleophilic terminator. A non-synchronous process is postulated, and the examples described strongly re-inforce our working mechanistic hypothesis, whereby the stereochemical course of cyclisation is directed by the orientation of the side chain vicinal to the intermediate cyclohexyl cation (see Schemes 4 and 5). It is also demonstrated that the efficiency of this process is independent of the nature of the OH group, which may be primary, secondary, or tertiary. In addition, the organoleptic properties of 12-14, Me homologs of known odorants such as Ambrox® ((-)-3a) and its diastereoisomer, are briefly discussed.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19930760417
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  • 7
    Electronic Resource
    Electronic Resource
    Dehydroalanine-Containing Peptides by AcOH-Elimination from O-Acetylserine Residuces with DBU/LiClO4 in Tetrahydrofuran (1993)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 76 (1993), S. 1702-1714 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The elimination of H2O from serine residues in peptides was found to be feasible by the following two steps: O-acylation with AcCl/pyrideine in CH2Cl2 and treatment with an imidine base (DBU or DBN) in THF in the presence of large amounts of LiClO4 (10 examples). Other Li salts such as LiBr and LiCl can also be used. No epimerization of the amino acid residues in te peptide could be detected under these conditions. Thus, a simple method for the preparation of peptides with dehydroalanine residues in high yield, directly from serine-containing precursors, is available.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19930760427
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  • 8
    Electronic Resource
    Electronic Resource
    C-Alkylation of Sarcosine Residues in Cyclic Tetrapeptides via Lithium Enlates (1993)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 76 (1993), S. 563-595 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The cyclic tetrapeptides cyclo(-Leu-Sar-Gly-), cyclo(-Val-Sar-Sar-Gly-), and cylco(-Meleu-Gly-D-Alasar-) have been synthesized from the component amino acids (BOP-Cl coupling), using the pentafluorophenyl esters for the cyclization step (42, 13, and 30% yield, respectively). Multiple deprotonation (LDA in THF/LiBr/DMPU) and addition of highly reactive electrophiles (CF3CO2D, MeI, CH2O, CH2CHCH2Br, PhCH2Br) produce cyclic tetrapeptides with additional substituents introduced diastereoselectively (70 to 〉 98% ds) in yields ranging from 20 to 90%. The C-alkylatd products are all derived from a sarcosine-enolate moiety adjacent to another N-methylamino acid. The structures of the resulting products are determined by NMR spectroscopy (DNOE and ROESY techniques) and by hydrolysis to the parent amino acids, suitable derivatization, and analysis by chromatography on a chiral GC column. It was shown in two cases that the overall yield of cyclization/alkylation to give a disubstitued cyclic tetrapeptide is higher than that of a synthesis of the same product from the corresponding amino-acid building blocks. Surprising temperature and salt effects on the yields and selectivities of the reactions of the cyclic tetrapeptide enolates are presented, and possible mechanistic interpretations are discussed.
    Additional Material: 14 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19930760138
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  • 9
    Electronic Resource
    Electronic Resource
    Crystal Structure of the Explosive Parent Benzyne Precursor: 2-Diazoniobenzenecarboxylate Hydrate (1993)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 126 (1993), S. 243-249 
    Details
    ISSN: 0009-2940
    Keywords: Benzyne precursor ; Neighboring group interactions ; Incipient nucleophilic attack ; 2-Diazoniobenzenecarboxylate ; Calculations, ab initio, MO ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structure of the highly unstable benzyne precursor 2-diazoniobenzenecarboxylate (3) has been determined by single-crystal X-ray diffraction. The structure is discussed in comparison to ab initio results for several conformers of 3, related aromatic diazonium ions, and phenyl cation and also to crystal structures of simple diazonium ion salts and of benzoates. Structural features and characteristic distortions are related to the electron density distributions and to intra- and intermolecular interactions between the neighboring functional groups.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19931260133
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  • 10
    Electronic Resource
    Electronic Resource
    Soluble (Phthalocyaninato)ruthenium(II) Phosphane Complexes (1993)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 126 (1993), S. 2565-2566 
    Details
    ISSN: 0009-2940
    Keywords: Phthalocyaninato complexes ; Ruthenium complexes ; Phosphanes ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hitherto unknown ruthenium phthalocyanine complexes with phosphane ligands - PcRu(PEt2Ph)2 (1) and PcRu(PPh3)2 (2) - soluble in common organic solvents were prepared. Two methods were used for their synthesis: 1) Reaction of phthalonitrile with [Ru2Cl3(PEt2Ph)6]Cl in n-pentanol in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and 2) reaction of PcRu with the corresponding phosphanes. The products 1 and 2 were characterized by their IR, UV/Vis, FD-MS, and 1H-NMR data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19931261136
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