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Glycosyl Imidates, 61. – Synthesis of the Hexasaccharide Moiety of the Saponin Holotoxin A

✍ Scribed by Han, Xiao-Bing ;Jiang, Zi-Hua ;Schmidt, Richard R.

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

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✦ Synopsis

Abstract

Reaction of O‐(3‐O‐methylglucosyl) trichloroacetimidate 2a as glycosyl donor and 1,2:5,6‐di‐O‐isopropylidene‐D‐glucofuranose (3) as glycosyl acceptor furnished in the presence of TMSOTf as catalyst the β‐(1→3)‐connected disaccharide 5a. Similarly, from O‐quinovosyl trichloroacetimidate 2b and 3 the disaccharide 5b was obtained. Compound 5a was transformed via acid‐catalyzed O‐deisopropylidenation, O‐acetylation, and selective 1‐O‐deacetylation into 7. Treatment of 7 with trichloroacetonitrile in the presence of DBU furnished trichloroacetimidate 8 as glycosyl donor. Reaction of 8 with 2,4‐O‐unprotected xylopyranoside 9 as glycosyl acceptor afforded selectively trisaccharide 10. Similarly, reaction of 8 with 2,4‐O‐unprotected quinovoside 12 furnished selectively trisaccharide 13 which gave upon O‐acetylation, 1‐O‐desilylation, and then treatment with trichloroacetonitrile in the presence of DBU trichloroacetimidate 15 as triosyl donor. Reaction of 10 with 15 in the presence of TMSOTf as catalyst led to hexasaccharide 16; ensuing hydrogenolytic O‐debenzylation and then O‐acetylation afforded the desired hexasaccharide 17.

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