Double glycosylation

Dehydrativeglycosylation of 1-hydroxy donors with Ph2S0/Tf20 in conjunction with thioglycoside acceptors opens the way for sequential double glycosylation, one-pot procedures for trisaccharide synthesis, as exemplified by the efficient one-pot synthesis of the a-Gal epitope and a hyaluronan trisaccharide [566]. This study also shows the potential of selenoglycoside as acceptors in dehydrative glycosylation (Scheme 4.112). 

A/ -alanyl, O-acyl and O-methylzeatin were discovered in Lupinus species [16-18], Fig. (1). Double glycosylated derivatives of cytokinins sucb as zeatin-9-(glucop3nianosyl riboside) were found to be most abundant components of cytokinin pool in mature pine buds [19]. Recently, a barley pathogen Pantoea agglomerans was found to excrete 2-methylthio-A/ -isopentenyladenine and its deoxyriboside, both having cytokinin activity, to the culture medium [20]. 

Double glycosylation has previously been accomplished on the solid support see Ref. 70. 

Scheme 5. Synthesis of double-glycosylated gpl20 glycopeptide...

Danishefsky has described the synthesis of 173 which represents the fully functionalized core of staurosporine, a potent protein kinase C inhibitor. Central to his strategy is incorporation and then unmasking of a double glycosyl donor by activation of (i) an endocyclic enol ether and (ii) an exocyclic enol ether, as outlined in Scheme 36. 

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