256449-39-5Relevant articles and documents
Acyl Transfer as a Problematic Side Reaction in Polymer-Supported Oligosaccharide Synthesis
Nukada, Tomoo,Berces, Attila,Whitfield, Dennis M.
, p. 9030 - 9045 (2007/10/03)
Under a wide variety of glycosylation conditions acyl transfer to the polymer support competed with glycoside formation, including the pivaloyl protecting group. As well as acyl transfer, many glycosylations also led to the formation of polymer-bound β-1,2-linked oligomers of the donor. Using ethyl 2,6-di-O-pivaloyl-3,4-O-isopropylidene-β-D-galactothiopyranoside as donor under promotion of N-iodosuccinimide/silver trifluoromethanesulfonate in the presence of 2-methyl-2-butene, an 82% yield of glycoside was obtained along with pivaloylated polymer. Subsequent work showed that increasing the steric bulk about the alcoholic acceptor in conjunction with this 2-O-pivaloyl-protected glycosyl donor completely suppresses this side reaction, giving a nearly quantitative yield of glycoside. This contraintuitive approach of decreasing the reactivity of both the donor and the acceptor to minimize a side reaction is rationalized by assuming that the barrier to acyl transfer is more sensitive to the protecting groups than that of glycosylation. These developments led to a polymer-supported synthesis of the branch point trisaccharide of the group B type 1A Streptococcus capsular polysaccharide.
