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  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1997 (1997), S. 1525-1528 
    ISSN: 0947-3440
    Keywords: Alkaloids ; Biomimetic synthesis ; spiro-Cyclization ; Marine sponges ; Natural products ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The alkylidene hydantoin 8 was synthesized as an analogue of the marine natural product oroidin (1) by employing a Horner-Wadsworth-Emmons reaction. Treatment of 8 with bromine in acetic acid induced a biomimetic spiro-cyclization forming the ACD ring system of dibromophakellin (2) in one step. rac-Midpacamide (10) was obtained from the same precursor through a chemoselective, ruthenium-catalyzed hydrogenation leaving the brominated pyrrole moiety intact.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0948-5023
    Keywords: Keywords: Computer-assisted structure elucidation ; Constitutional analysis ; HMBC ; ADEQUATE ; NMR software
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The constitutional assignment of natural products by NMR spectroscopy is usually based on 2D NMR experiments like COSY, HSQC, and HMBC. In this paper, the resulting connectivity information is used as input for the new structure generating program Cocon which both improves and dramatically accelerates the process of constitutional assignment. Cocon allows to quantify the value of connectivity information (2D NMR correlation data) for structure elucidation problems. Applying Cocon, it is systematically evaluated to which degree the NMR experiments COSY, 1H,13C-HMBC and 1,1-ADEQUATE constrain the number of constitutions compatible with the data sets of two secondary metabolites from marine sponges.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-1561
    Keywords: Chemical defense ; sponges ; predation ; Agelas ; pyrrole–imidazole alkaloids ; structure–activity relationship ; synthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract We investigated the relationship between the structures of pyrrole-containing alkaloids from marine sponges of the genus Agelas and their capacity to deter feeding by the omnivorous Caribbean reef fish, Thalassoma bifasciatum. Seven natural products were assayed at volumetric concentrations of 1, 5, and 10 mg/ml: dispacamide A, keramadine, oroidin, midpacamide, 4,5-dibromopyrrole-2-carboxylic acid, 4,5-dibromopyrrole-2carboxamide, and racemic longamide A. We also assayed 14 structural analogs obtained mostly by chemical synthesis. Of the seven natural products, only rac-longamide A was not significantly deterrent at any of the assay concentrations. The pyrrole moiety was required for feeding inhibition activity, while the addition of the imidazole group enhanced this activity. Variously functionalized imidazoles lacking the pyrrole moiety were not deterrent. Combinations of the natural products appeared to have an additive effect on feeding inhibition; there was no evidence of synergy. Given their high concentrations in sponge tissue, dispacamide A and oroidin most probably serve as the primary chemical defenses of many Agelas sp., while minor compounds such as keramadine are not present in high enough concentrations to contribute much to chemical defense.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1434-193X
    Keywords: Structure elucidation ; Constitutional analysis ; Natural products ; HMBC ; Computational chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The computer program COCON is introduced as a tool for the comprehensive structure elucidation of unknown organic compounds. In particular, structural proposals made on the basis of the molecular formula and of 2D-NMR experiments can be analyzed for the existence of alternative constitutions being in agreement with the same data set. The computational speed grounds on the evaluation of ambiguous long-range connectivity information during the process of structure generation. The data set experimentally obtained for the marine natural product oroidin (1) was selected, because proton-poor compounds usually cause uncertainties in NMR-based structure determinations. The calculation results encourage to move from the experience-based analysis of NMR chemical shifts or of MS fragmentations to the automated evaluation of routinely available connectivity information.Supporting information for this article is available on the WWW under -http://www.wileY-Vch.de/contents/jc_2046/1999/98241_s.pdf or from the author.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1434-193X
    Keywords: Structure elucidation ; Computational method ; Natural products ; HMBC ; Constitutional analysis ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The application of the new computer program COCON (Constitutions from Connectivities) to the 2D-NMR data sets of three different complex natural products is described. The investigated compounds are proton-poor and therefore underdetermined systems. For such molecules the number of possible constitutions and the computational speed of COCON are of interest. Our investigation is focused on how methods of 13C-NMR chemical shift prediction can assist chemists with regard to refining the selection among the constitutions proposed by COCON.
    Additional Material: 6 Ill.
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  • 6
    Publication Date: 2016-03-23
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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