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

Abstract

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.

Palladium-Controlled β-Selective Glycosylation in the Absence of the C(2)-Ester Participatory Group

“…The glycosyl trichloroacetimidates are generally activated with strong and moisture sensitive Lewis acids such as BF 3 ·OEt 2 , TMSOTf, TBSOTf, Tf 2 O, and ZnBr 2 ; BF 3 ·OEt 2 has been among the widely used Lewis acids . Glycosylation of galactosyl nucleophile 5 with trichloroacetimidate 4 was performed with 1 mol % of BF 3 ·OEt 2 at −78 °C so that we can determine the reactivity and selectivity of BF 3 ·OEt 2 compared to that of cationic Pd(II) species, Pd(PhCN) 2 (OTf) 2 (Scheme ).…”

Recent Advances in Transition Metal-Catalyzed Glycosylation

“…Since Schmidt first developed his glycosylation protocol in the 1980s, − the trichloroacetimidate leaving group has been one of the most widely used glycosyl donors, its popularity stemming from ease of preparation via base-catalyzed addition of trichloroacetonitrile to the anomeric hydroxyl group. − The glycosyl trichloroacetimidate is usually activated with strong and moisture-sensitive Lewis acids, such as BF 3 ·OEt 2 , ,, TMSOTf, ,− TBSOTf, Tf 2 O, and ZnBr 2 . However, there are drawbacks to their use in glycosylation, such as low reaction temperature requirements for avoiding decomposition of acid-sensitive substrates and anhydrous reaction conditions.…”

“…C(2)-Amino sugars are a key component of glycoproteins that are found on cellular surfaces and serve as receptor ligands for enzymes and other macromolecules. − Glycosides of C(2)-amino sugars are linked to other carbohydrates or amino acids via either a 1,2-cis or a 1,2-trans linkage. Direct synthesis of 1,2- trans -2-aminoglycosides can be accomplished by incorporating participating groups at the C(2) position of glycosyl donors; however, selective formation of the 1,2- cis -2-amino glycosides remains problematic because of the necessity for nonparticipating groups at C(2) of the donor. − Even though there have been a variety of methods reported for stereo­selective construction of 1,2- cis -2-amino sugars, − ,,,,,− each have their own set of disadvantages or limitations. The Nguyen group has made recent advances to overcome these limitations using cationic nickel(II) catalysis. , …”

Glycopeptide Synthesis

“…Application of a glucosyl halide derivative with an acyl group in the 2-position directs the β-bond formation with an appro priately protected chitobiose acceptor. After the acyl group has been selectively removed from the donor the free hydroxy group is either oxidized to the ketone and reduced affording preferentially the manno configuration (Ekborg et al, 1972) or transformed into a leaving group and substituted with inversion of configuration by a neighboring car bamoyl group (Gunther and Kunz, 1992) or with other nucleophiles (Paulsen et al, 1992).…”