Highly stereoselective synthesis of alpha,beta-linked, nonreducing disaccharides related to tunicamycin.
3,4,6-Tri-O-benzoyl-2-(benzoyloxyimino)-2-deoxy-alpha-D-arabino-++ +hexopyranosy l bromide (2) reacts with the O-protected 2-deoxy-2-phthalimido-beta-D-galactosamines 3 and 4 in the presence of silver triflate and sym-collidine at -78 degrees C, to give alpha,beta-(1-->1)-linked disaccharides 6a and 7a with an excellent selectivity. The 2-oxyimino function was stereospecifically converted into a 2-acetamido group by use of the LiBH4-Me3SiCl-THF reductive species, furnishing, after acetylation, the alpha-D-GlcNAc-(1-->1)-beta-D-GalNPhth nonsymmetrical, trehalose type disaccharides 13 and 14 related to tunicamycin (1, part A). Similarly, alpha-D-GlcNAc-(1-->1)-beta-D-GlcNPhth (15) was prepared, starting from 2 and 5. The factors governing the stereoselectivity of the glycosylation reactions were determined.
Institute of Organic Chemistry, Polish Academy of Sciences, Warsaw.
W
W
Karpiesiuk
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A
Banaszek
D002236:Carbohydrate Conformation; D004187:Disaccharides / Q000138:chemical synthesis*; D015394:Molecular Structure; D010084:Oxidation-Reduction; D014415:Tunicamycin / Q000737:chemistry*
D004187:Disaccharides; D014415:Tunicamycin