Bausteine von Oligosacchariden, CIV. Synthese von verzweigten Tetrasaccharid‐ und Pentasaccharid‐Strukturen von N ‐Glycoproteinen, methyliert an 4′‐OH des Verzweigungsgliedes

Building Units of Oligosaccharides, CIV. — Synthesis of Branched Tetrasaccharide and Pentasaccharide Structures of N ‐Glycoproteins Methylated at 4′‐OH of the Branching Unit The tetrasaccharide α‐ D ‐Man p ‐(1→3)[α‐ D ‐Man p ‐(1→6)]‐4‐ O ‐methyl‐β‐ D ‐Man p ‐(1→4)‐ D ‐GlcNAc ( 15 ) and the pentasaccharide β‐ D ‐Glc p NAc‐(1→2)‐α‐ D ‐Man p ‐ (→3)[α‐ D ‐Man p ‐(→6)]‐4‐ O ‐methyl‐β‐ D ‐Man p ‐ (→4)‐ D ‐GlcNAc ( 23 ) were synthesized by adding the respective functionalized building blocks. The compounds are useful for studies of the substrate specificities of GlcNAc transferases I and II in the biosynthesis of N‐linked oligosaccharides, respectively. In addition we developed an effective synthesis for the β‐glycosidically linked building block β‐ D ‐Man p ‐(→4)‐α‐ D ‐Glc p NAc. The trichloroacetimidate method was particularly successful for synthesizing these glycosidic linkages.