Chain Extension of Carbohydrates VI^<1)>. Synthesis of the Two C-6 Epimers of the 6-Acetylamino-4,6-dideoxyheptopyranosiduronic Acid Present in Amipurimycin by Means of Stereocontrolled Ethynylation of Methyl 2,3-Di-O-benzyl-4-deoxy-α-_D-xylo-hexodialdo-1,5-pyranoside

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Abstract

The two C-6 epimers of 6-acetylamino-4,6-dideoxy-heptopyranosiduronic acid present in amipurimycin were prepared by selective reactions from methyl 2,3-di-<i>O</i>-benzyl-4,6,7,8-tetradeoxy-<i>α</i>-<FONT SIZE="-2">L</FONT>-<i>ido</i>-7-ynopyranoside (<b>4</b>) in which the ethynyl group was employed as a precursor of the carboxylic acid function. The masked amino group was introduced at C-6 by reaction of <b>4</b> with zinc azide in the presence of triphenylphosphine and diisopropyl azodicarboxylate. The resulting methyl 6-azido-2,3-di-<i>O</i>-benzyl-4,6,7,8-tetradeoxy-<i>α</i>-<FONT SIZE="-2">D</FONT>-<i>gluco</i>-oct-7-ynopyranoside (<b>5</b>) was transformed into benzyl[6-(acetylamino)-2,3-di-<i>O</i>-benzyl-4,6-dideoxy-<i>α</i>-<FONT SIZE="-2">D</FONT>-<i>gluco</i>-heptopyranosid]uronate (<b>7</b>) by two different sequences of reactions: (1) oxidative cleavage of the triple bond, benzylation, reduction of the azido group, <i>N</i>-acetylation or (2) reduction of the azido group, <i>N</i>-acetylation, oxidative cleavage of the triple bond and treatment with phenyldiazomethane. The second sequence of reactions was found to be more efficient (33% overall yield versus 13%). The configuration at C-6 was unambiguously confirmed by X-ray diffraction with a single crystal of <b>7</b>. Final hydrogenolysis of benzyl groups afforded methyl 6-(acetylamino)-4,6-dideoxy-<i>α</i>-<FONT SIZE="-2">D</FONT>-<i>gluco</i>-heptopyranosiduronic acid (<b>9</b>). A Mitsunobu reaction on acetylenic alcohol <b>4</b> followed by saponification afforded the C-6 epimer <b>11</b>. The same sequences of reactions was applied to <b>11</b> and methyl 6-(acetylamino)-4,6-dideoxy-<i>α</i>-<FONT SIZE="-2">L</FONT>-<i>ido</i>-heptopyranosiduronic acid (<b>16</b>) was obtained.

Journal

  • Bulletin of the Chemical Society of Japan

    Bulletin of the Chemical Society of Japan 69(5), 1347-1351, 1996-05-15

    The Chemical Society of Japan

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Codes

  • NII Article ID (NAID)
    10008903234
  • NII NACSIS-CAT ID (NCID)
    AA00580132
  • Text Lang
    ENG
  • Article Type
    ART
  • ISSN
    00092673
  • Data Source
    CJP  J-STAGE 
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