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Glycosyl Imidates, 62. – Synthesis of the Heptasaccharide Moiety of Ganglioside BGM1

✍ Scribed by Greilich, Ulrike ;Zimmermann, Peter ;Jung, Karl-Heinz ;Schmidt, Richard R.

Publisher
John Wiley and Sons
Year
1993
Tongue
English
Weight
661 KB
Volume
1993
Category
Article
ISSN
0947-3440

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✦ Synopsis

Abstract

The synthesis of the O‐acetyl protected heptasaccharide moiety (2) of BGM~1~ was performed according to the following reaction sequence: Reaction of 2,3‐di‐O‐acetyl‐4,6‐O‐benzylidenegalactosyl trichloroacetimidate 4 (as donor) with 3‐O‐unprotected 2‐azidogalactose 5 (as acceptor) gave β(1→3)‐connected disaccharide 6. Subsequent O‐deacetylation followed by reaction with galactosyl donor 8 afforded regioselectively trisaccharide 9 which was converted into tetrasaccharide 12 by treatment with fucosyl donor 11. Transformation of 12 via acid‐catalyzed O‐deisopropylidenation, O‐acetylation, anomeric O‐desilylation, and then base‐catalyzed treatment with trichloroacetonitrile afforded trichloroacetimidate 16 as tetraosyl donor. Reaction of 16 with the known 4b‐O‐unprotected sialyllactose derivative 17 gave in acetonitrile at −40°C in the presence of TMSOTf as the catalyst the desired heptasaccharide 18. Azido group reduction with propanedithiol, N‐acetylation, hydrogenolytic O‐debenzylation, and O‐debenzylidenation under acidic conditions followed by O‐acetylation afforded the target molecule 2. The structural assignments were based on the ^1^H‐NMR data.

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