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  • 1
    Electronic Resource
    Electronic Resource
    Synthetic routes to 1,4-difunctionalized cycloheptenesDedicated to Professor Dr. Richard R. Schmidt on the occasion of his 60th birthday. (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 1843-1848 
    Details
    ISSN: 0947-3440
    Keywords: Enediynes ; [2 + 2] Cycloaddition ; Bicyclo[3.2.0]heptanes ; Fragmentation ; Ring closing metathesis ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two routes to 1,4-difunctionalized cycloheptenes are described. The first one is based on a fluoride-induced fragmentation reaction of the bicyclic [3.2.0]heptanesilyl monosulfate 10. This compound in turn was prepared by a ketene-cyclopentene cycloaddition route. An alternative strategy took advantage of a ring-closing metathesis (RCM) reaction of the diolefin 18 with the ruthenium catalyst 21. This reaction proved to be reliable even on a larger scale and allowed the isolation of the cycloheptene 19a in reasonably good yield.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1995199510258
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  • 2
    Electronic Resource
    Electronic Resource
    Design and Synthesis of Dynemicin Analogs (1999)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1999 (1999), S. 1-13 
    Details
    ISSN: 1434-193X
    Keywords: Dynemicin ; Enediynes ; Antitumor agents ; Antibiotics ; Cross-coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -Dynemicin A is a member of the family of enediyne natural products. It is unique in that it combines a ten-membered enediyne with an anthraquinone substructure. These features stimulated the development of synthetic approaches to the natural product itself and of analogs thereof. This review summarizes the total syntheses of dynemicin A. In addition, an overview of the known analogs is presented. The analogs can be classified according to the designed trigger mechanism. Most of the analogs contain a removable carbamate on the nitrogen atom. Others are quite similar to the natural lead in that they contain a quinone substructure, which upon reduction causes opening of the oxirane ring. In addition, there are analogs that contain an aromatic sector, the enediyne, and the oxirane ring but lack the nitrogen heterocycle. In these compounds the aryl ring assumes a different conformation from that in dynemicin A. Many of the simplified analogs proved to be quite active in vitro as well in vivo against murine tumor models. A highlight is compound 30 which is much more active than dynemicin A itself. However, looking at all analogs there is no clear-cut correlation between the DNA-cleaving ability at neutral pH and the in vitro results. From this one might conclude that there are possibly two mechanisms for antitumor activity. One involves diradical formation whereas the other might be due to a ligand-receptor interaction.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Synthesis and Reactivity of a p-Methoxyphenyl-Substituted Enediyne. A Case of Electronic Influence on the Rate of the Bergman Cycloaromatization (1992)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1992 (1992), S. 855-861 
    Details
    ISSN: 0170-2041
    Keywords: Enediynes ; 1,5 Diynes ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Bicyclo[7.3.1]diynes 19a and 19b were prepared by using dibromo olefin 11 and ketone 12 as building blocks. The key step of the synthetic sequence is an intramolecular Nicholas reaction of 17 to give the bicyclo[7.3.1]diyn-10-one dicobalthexacarbonyl adducts 18a and 18b (66% total yield). Oxidative decomplexation of 18a and 18b with cer(IV) ammonium nitrate gave the diynes 19a and 19b, respectively. Both diynes 19a and 19b could be oxidatively converted into the enediyne 20 by using DDQ. In contrast to the unsubstituted enediyne 4, compound 20 can be isolated at room temperature Quantitative kinetic measurements of the rate of the Bergman cyclization of 20 gave ΔG# (37°C) = 111 kJ mol-1. This value is 12.3 kJ mol-1 higher than that of 4. The difference in the free activation energy between 20 and 4 is attributed to electronic effects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1992199201140
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  • 4
    Electronic Resource
    Electronic Resource
    Synthesis of 11-Membered Enediyne Ketones by the Intramolecular Nicholas Reaction (1993)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1993 (1993), S. 1009-1016 
    Details
    ISSN: 0170-2041
    Keywords: Enediynes ; Nicholas reaction ; Macrocycles ; Eleven-membered rings ; Calculations, force-field ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An efficient route to 11-membered enediyne ketones 13 and 22 was developed. This route is based on an intramolecular Nicholas reaction of 11 and 20, respectively. In the course of the preparation of the cyclization substrates 11 and 20, it was important to use the acetylenic alcohols 6 and 15 as building blocks for the construction of the cis-enediynes 8 and 17, respectively, instead of the corresponding ketones which were converted into unstable acyclic enediynes. Some transformations of enediyne ketone 22 were also studied. For example, 22 could be transformed into the 2-formyl compound 26 via the silyl enol ether 24. In addition, 24 was used for the preparation of the 2-amino ketone 29.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.1993199301160
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