Bausteine von Oligosacchariden, LXXIV. Synthese von verzweigten Tri‐ und Tetrasaccharidsequenzen der „Repeating Unit”︁ der O‐spezifischen Kette des Lipopolysaccharides aus Aeromonas salmonicida

Abstract

Es wird die „Repeating unit”︁ des O‐Antigens des Lipopolysaccharides von Aeromonas salmonicida in der Form α‐D‐Glcp‐(1→3)‐[β‐D‐ManpNAc‐(1→4)]‐L‐Rha (17) und α‐D‐Glcp‐(1→4)‐α‐D‐Glcp‐(1→3)‐[β‐D‐Manp NAc‐(1→4)]‐L‐Rha (27) synthetisiert. Schlüsselreaktionen sind hierbei die Herstellung der β(1→4)‐glycosidischen Bindung zwischen 2‐Acetamido‐2‐desoxy‐D‐mannose und L‐Rhamnose sowie die Knüpfung der α(1→3)‐glycosidischen Bindung von Glucose und von Maltose mit dem Disaccharid 10 als Glycosyl‐Akzeptor.

2-Oxoglycosyl (“Ulosyl”) and 2-Oximinoglycosyl Bromides: Versatile Donors for the Expedient Assembly of Oligosaccharides with β-d-Mannose, β-l-Rhamnose, N-Acetyl-β-d-mannosamine, and N-Acetyl-β-d-mannosaminuronic Acid Units

“…An alternate means of constructing β- d -ManNAc-(1→4)- l -rhamnoside 236 has been devised via glycosylation of a 4-OH-free rhamnoside with 2-azidomannosyl bromide 197 . However, this donor is difficultly accessible (11 steps from d -glucose in 10% overall yield), must be used in situ due to its high sensitivity, and requires a 6-fold excess of the rhamnosyl acceptor to avoid loss of its 6- O -benzyl group toward formation of the 1,6-anhydro derivative .…”

“…An alternate means of constructing β- d -ManNAc-(1→4)- l -rhamnoside 236 has been devised via glycosylation of a 4-OH-free rhamnoside with 2-azidomannosyl bromide 197 . However, this donor is difficultly accessible (11 steps from d -glucose in 10% overall yield), must be used in situ due to its high sensitivity, and requires a 6-fold excess of the rhamnosyl acceptor to avoid loss of its 6- O -benzyl group toward formation of the 1,6-anhydro derivative . The oximinoglycosyl donors 205 and 213 , by contrast, are comparatively well accessible, in 59% and 50% yield for the six and seven steps, respectively, from d -glucose,are crystalline, storable compounds, and are glycosidated with 20:1 β-selectivities (vide supra, section 3.3.1).…”