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  • 1
    Electronic Resource
    Electronic Resource
    Pteridines. Part LXXXVIIPart LXXXVI [1].. Synthesis and Properties of 8-Substituted 2-Thiolumazines (1988)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 71 (1988), S. 1379-1391 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Various 8-substituted 2,8-dihydro-2-thioxopteridin-4(3H)-ones (14-21) and 2-(methylthio)pteridin-4(8H)-ones (27-32) have been synthesized by condensation of the appropriate 5-amino-6-(substituted amino)-1,2-dihydro-2-thioxopyrimidin-4(3H)-ones (22-34) and 5-amino-6-(substituted amino)-2-(methylthio)pyrimidin-4(3H)-ones (25, 26), respectively, with glyoxal, biacetyl, and benzil. The presence of a quinonoid cross-conjugated π-electron system makes this type of compounds susceptible to nucleophilic additions in position 7, which leads to intramolecular (43, 45) and intermolecular (44) covalent adducts. The newly synthesized compounds have been characterized by elemental analyses, pKa determinations, 1H-NMR and UV spectra. UV-Spectral changes in dependence of the pH are associated with the most appropriate molecular species including the monocations, neutral forms, covalent adducts, mono- and dianions.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19880710602
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  • 2
    Electronic Resource
    Electronic Resource
    Pteridines. Part XLIPart XL, see[1]. Synthesis and properties of 6,7,8-trimethyl-4-thiolumazine (1989)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 72 (1989), S. 738-743 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The first representative of the 8-substituted 4-thiolumazine series has been synthesized. In a sequence of reactions, 4,6-dichloropyrimidin-2-(1H)-one (1) is first converted into 4-chloro-6-(methylamino)pyrimidin-2(1H)-one (6), then the Cl-atom displaced by the thioxo group (→7) followed by a coupling reaction with 4-chlorophenyldiazonium chloride to introduce the necessary N-function into the 5-position (→ 9; Scheme 1). Reduction of the p-chlorophenylazo group leads to the 6-(methlyamino)-4-thiouracil-5-amine (10) which on condensation with diacetyl gives 6,7,8-trimethyl-4-thiolumazine (8). The physical properties of 8 are compared with the 2-thio analog and 6,7,8-trimethyllumazine indicating that 8 possesses the highest acidity and the longest UV absorption.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19890720414
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  • 3
    Electronic Resource
    Electronic Resource
    Pteridines. Part XLIIPart XLI, see [1]. Synthesis and properties of 8-substituted 2,4-dithiolumazines (1989)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 72 (1989), S. 744-755 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Condensation reactions of the 5-amino-6-(subst. amino)-2,4-dithiouracils 12 and 13 with diacetyl or benzil led to the 6,7,8-trisubstituted 2,4-dithiolumazines 14-16. Methylation of these compounds affected both thio functions forming various types of 2,4-bis(methylthio)lumazine derivatives depending on the nature of the substituents at C(7) and N(8). The 6,7,8-trimethyl-2,4-dithiolumazine (14) was converted into 7,8-dihydro-6,8-dimethyl-7-methylidene-2,4-bis(methylthio)pteridine (17), whereas the 8-methyl-6,7-diphenyl-(15) and the 8-(2-hydroxyethyl)-6,7-diphenyl-2,4-dithiolumazine (16) yielded the corresponding covalent inter- or intramolecular 7,8-adducts 18-21. The unusual structures were proven by spectroscopic means and those of the alcohol adducts 20 and 21, furthermore, confirmed by X-ray analysis.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19890720415
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