NOVEL GLYCOSIDATION METHODOLOGY - THE USE OF PHENYL SELENOGLYCOSIDES AS GLYCOSYL DONORS AND ACCEPTORS IN OLIGOSACCHARIDE SYNTHESIS

The use of phenyl selenoglycosides as glycosyl donors and acceptors in glycosidation reactions is described. The versatility of these novel compounds is illustrated by the selective activation of both ''disarmed'' and ''armed'' phenyl selenoglycoside donors over ''armed'' ethyl thioglycoside acceptors with silver trifluoromethanesulfonate in the presence of potassium or silver carbonate to give disaccharides in excellent yield. Selective activation of glycosyl bromide donors over phenyl selenoglycoside acceptors is realized by silver trifluoromethanesulfonate promotion in the presence of collidine. Such selectivity is also demonstrated by the activation of a glycosyl trichloroacetimidate donor in the presence of selenoglycoside acceptors with triethylsilyl trifluoromethanesulfonate. The central role of selenoglycosides is illustrated by the synthesis of a trisaccharide that profits from the sequential, selective activation of a glycosyl bromide donor over a selenoglycoside acceptor and the resulting disaccharide selenoglycoside over a thioglycoside acceptor. The liberation of the anomeric hydroxyl group from a phenyl selenoglycoside is also described.