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  • Natural products  (10)
  • Wiley-Blackwell  (10)
  • Blackwell Publishing Ltd
  • Elsevier
  • 2000-2004  (10)
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  • Wiley-Blackwell  (10)
  • Blackwell Publishing Ltd
  • Elsevier
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1609-1615 
    ISSN: 1434-193X
    Keywords: Terpenoids ; Natural products ; Total synthesis ; Cyclizations ; Rearrangements ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A new route for the synthesis of 2,7- and 7-functionalized labdanes starts from (R)-carvone (1). 11-Nordrim-7-en-9-one (15) is an appropriate starting material for the total synthesis of hispanone (21), a biologically active furolabdane isolated from the Mediterranean medicinal plant Ballota saxatilis.
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1623-1626 
    ISSN: 1434-193X
    Keywords: Iridoid glucoside ; (8S)-Kingiside ; (8S)-Loganin ; (8S)-7-Ketologanin ; Asymmetric synthesis ; Natural products ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The tetraacetyl derivative 8 of the naturally occurring kingiside (8a) was prepared from aucubin (1). Intermediates in the synthesis were (8S)-tetraacetyl loganin (6) and (8S)-tetraacetyl-7-ketologanin (7), whose free (8R)-epimers occur in many different plants (Caprifoliaceae, Loganiaceae). The 13C NMR spectrum allows the structure to be unequivocally identified.
    Additional Material: 1 Tab.
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  • 3
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 849-855 
    ISSN: 1434-193X
    Keywords: Marine alkaloids ; Heterocycles ; Natural products ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Ascididemine (9H-quino[4,3,2-de][1,10]phenanthrolin-9-one) (1) and an isomer (9H-quino[4,3,2-de][1,7]phenanthrolin-9-one) (4) have been synthesized starting from 1,4-dimethoxyacridone (7). The acridone was converted into 1,4-dimethoxy-9-ethynylacridine (11) by a triflate coupling. The ethynylacridine was converted in one-pot into 3H-6-methoxypyrido[2,3,4-kl]acridine (15) by reaction with sodium diformylamide; the mechanism of this key transformation is discussed. Conversion into 6H-4-bromopyrido[2,3,4-kl]acridin-6-one (19) and 6H-pyrido[2,3,4-kl]acridin-6-one (17), followed by reaction of each of these under high pressure conditions with acrolein N,N-dimethylhydrazone, gave ascididemine and its isomer, respectively.
    Additional Material: 2 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 73-82 
    ISSN: 1434-193X
    Keywords: Natural products ; Oxa-conjugate addition ; Rearrangement ; Tetrahydropyrans ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---Intramolecular oxa-conjugate addition has been employed in a stereoselective synthesis of enantiopure polyalkyl-substituted tetrahydropyrans, which are frequently found as substructures in many natural products. The requisite cyclization precursors, 7-hydroxy-2-enimides 3 and 7-hydroxy-2-enoates 6 were easily accessible by silyloxy Cope rearrangements of the appropriate chiral syn-aldols. It was found that the stereoselectivity of the cyclization could be controlled by judicious choice of the carboxylic acid derivative, resulting in a kinetically controlled reaction for the imides and a thermodynamically controlled process for the esters. Mechanistic considerations that could account for the stereocontrol of the process are outlined.
    Additional Material: 3 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 729-735 
    ISSN: 1434-193X
    Keywords: Rubromycins ; Natural products ; Biosynthesis ; Quinones ; Structure elucidation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The structure of the known secondary metabolite β-rubromycin was corrected, based on spectroscopic and chemical investigations, from o-quinone 1 to p-quinone 6. By feeding [U-13C3]malonic acid to the rubromycin-producing strain, Streptomyces sp. A1, the polyketide origin of the skeleton was verified, but the identity of the starter unit and the folding mechanism of the polyketide chain are still unclear. From the culture broth of the strain A1, in addition to 6, the co-metabolites γ-rubromycin (3), δ-rubromycin (4) and 3′-hydroxy-β-rubromycin (7) were isolated. Their structures were determined or confirmed by detailed spectroscopic analysis. The rubromycins inhibit HIV-1 reverse transcriptase (RT) and are cytostatically active against different tumor cell lines.
    Additional Material: 1 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1387-1389 
    ISSN: 1434-193X
    Keywords: Natural products ; Epoxidations ; Asymmetric synthesis ; Fluorine ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The synthesis of enantiomerically and diastereomerically pure (-)-(1R,2R,5R)- and (-)-(1R,2S,5R)-2-fluoro frontalin (7) starting from (+)-(1S)-menthyl-(R)-toluene-4-sulfinate, methylmagnesium bromide, methyl fluoroacetate, 4-pentenyl bromide and diazomethane is described. The absolute stereochemistry was unambiguously determined by X-ray analysis of (+)-(1S,2R,5S,RS)-5, an intermediate in the synthesis of the enantiomeric (+)-(1S,2R,5S)-2-fluoro frontalin (7).
    Additional Material: 2 Ill.
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  • 7
    ISSN: 1434-193X
    Keywords: Diarrhetic Shellfish Poisoning ; NMR spectroscopy ; Yessotoxin ; Natural products ; Carboxyyessotoxin ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A new analogue of yessotoxin (YTX), carboxyYTX, 3, was isolated from the digestive glands of mussels cultured on the Italian Adriatic coast. Its structure was determined by MS and NMR spectroscopy.
    Additional Material: 3 Ill.
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  • 8
    ISSN: 1434-193X
    Keywords: Natural products ; Starfish ; LC-NMR-MS hyphenation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -LC-NMR-MS hyphenation has been applied in the screening of an asterosaponin subfraction obtained from the starfish Asterias rubens for unknown compounds. The suitability of this technique for characterizing compounds in the molecular weight range of 1200 to 1400 a.m.u. has been demonstrated. The additional information concerning the number of exchangeable protons provided by the LC-NMR-MS experiment proved to be particularly valuable for the structural elucidation. The LC-NMR-MS screening indicated the presence of hitherto unknown asterosaponins in the sample. Based on this information, four new compounds (ruberosides A-D; 2-4 and 6) have been isolated and their structures have been elucidated using one- and two-dimensional NMR techniques. A minor component has tentatively been assigned the structure 5.
    Additional Material: 5 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1313-1317 
    ISSN: 1434-193X
    Keywords: Leishmaniasis ; Natural products ; Phytochemistry ; Quinones ; C-C coupling ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -The first synthesis of diospyrin [2,6′-bis(5-hydroxy-7-methyl-1,4-naphthoquinone), 1] was achieved by employing Suzuki coupling between 5 and 14 as the key reaction to connect the two 7-methyljuglone units.
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1889-1904 
    ISSN: 1434-193X
    Keywords: Total synthesis ; Natural products ; Squamocin A ; Squamocin D ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---The total syntheses of the Annonaceous acetogenins squamocin A and squamocin D have been achieved. The synthesis follows a modular strategy, wherein a left-side chain, the central bis-THF core and the right-side chain are assembled together. Key reactions are additions of organomagnesium compounds to bi-THF aldehydes. At the end of the synthesis the butenolide moiety was introduced. This modular synthetic approach should be useful for the synthesis of other related natural products as well as pharmacologically interesting analogs.
    Additional Material: 1 Ill.
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