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-O-benzyl-4,6,7,8-tetradeoxy-α-l-ido-7-ynopyranoside (4) 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 4 with zinc azide in the presence of triphenylphosphine and diisopropyl azodicarboxylate. The resulting methyl 6-azido-2,3-di-O-benzyl-4,6,7,8-tetradeoxy-α-d-gluco-oct-7-ynopyranoside (5) was transformed into benzyl[6-(acetylamino)-2,3-di-O-benzyl-4,6-dideoxy-α-d-gluco-heptopyranosid]uronate (7) by two different sequences of reactions: (1) oxidative cleavage of the triple bond, benzylation, reduction of the azido group, N-acetylation or (2) reduction of the azido group, N-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 7. Final hydrogenolysis of benzyl groups afforded methyl 6-(acetylamino)-4,6-dideoxy-α-d-gluco-heptopyranosiduronic acid (9). A Mitsunobu reaction on acetylenic alcohol 4 followed by saponification afforded the C-6 epimer 11. The same sequences of reactions was applied to 11 and methyl 6-(acetylamino)-4,6-dideoxy-α-l-ido-heptopyranosiduronic acid (16) was obtained.
The tetrasaccharide a-D-Manp-(l-3) [a-D-Manp-( 1+6)]-4-0-of GlcNAc transferases I and I1 in the biosynthesis of N-linked methyl-P-~-Manp-( 1+4)-~-GlcNAc (15) and the pentasacchar-oligosaccharides, respectively. In addition we developed an ide p-~-GlcpNAc-( 1+2)-a-~-Manp-( 1-3) [u-~-Manp-( 1-41-4effective synthesis for the P-glycosidically linked building O-methyl-P-~-Manp-(1+4)-~-GlcNAc (23) were synthesized block P-~-Manp-(1+4)-a-~-GlcpNAc. The trichloroacetimiby adding the respective functionalized building blocks. The date method was particularly successful for synthesizing these compounds are useful for studies of the substrate specificities glycosidic linkages.
Building Units of Oligosaccharides. Part 104. Synthesis of Branched Tetrasaccharide and Pentasaccharide Structures of N-Glycoproteins Methylated at 4'-OH of the Branching Unit. -The tetrasaccharide (Ia) and the pentasaccharide (Ib) are synthesized by adding the respective functionalized building blocks. The compounds are useful for studies of the substrate specificities of N-glucosaminyltransferases I and II in the biosynthesis of N-linked oligosaccharides. -(PAULSEN, H.; WILKENS, R.; RECK, F.; BROCKHAUSEN, I.; Liebigs Ann.
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