Facile Synthesis of per-O-tert-Butyldimethylsilyl-β-d-galactofuranose and Efficient Glycosylation via the Galactofuranosyl Iodide

Abstract

The synthesis of crystalline per-O-TBS-beta-D-galactofuranose (4beta) as a new precursor of D-Gal f units is described. Anomeric iodination by reaction with TMSI followed by in situ coupling with simple alcohols and a wide variety of glycosyl acceptors, in the absence of a promoter, was employed as a new efficient glycosylation method for the assembly of D-galactofuranosyl moieties with high beta-stereoselectivity. Under the mild conditions of this reaction labile protective groups, like acetals, and furanosyl linkages are preserved.

Chemical Synthesis of Furanose Glycosides

“…This method has been applied both to D-arabinose (47) and D-galactose (48), and the resulting derivatives have been converted to other species that are suitable for use in glycosylation reactions.…”

Synthetic tools for the characterization of galactofuranosyl transferases: glycosylations via acylated glycosyl iodides

“…with 9-decen-1-ol under the conditions previously described, 18 afforded glycoside 14 in 83 % yield as an anomeric mixture / in a 3:1 ratio. A similar diastereoselectivity was observed with simple acceptors, which was increased when bulky acceptors were used.…”

“…Compound 12 was effectively glycosylated to afford O-, 18 S-, C-galactofuranosides, 20 and some nitrogenated derivatives, 19 under mild conditions compatible with labile acceptors.…”

“…For the synthesis of 2 it was necessary to introduce the alkenyl moiety with a glycosylation method that would preserve the Galf-(1→3)-Manp linkage. We decided to carry on this synthesis by two alternative approaches: one based on the trichloroacetimidate method, which required transformations that we have previously applied, 17,18 and the other involving a glycosyl iodide donor (Scheme 1). In this case, the conditions for the glycosylation of the acetylated mannose unit must be established.…”

“…The optimized conditions for the synthesis of 3 would be useful for the glycosylation of 1. On the other hand, as continuation of our studies on the scope of glycosylations via galactofuranosyl iodides, [18][19][20] For the synthesis of mannopyranoside 3 we used the glycosyl iodide method starting from penta-O-acetyl--D-mannopyranose (5). In first instance, we established the reaction conditions for the formation of the mannopyranosyl iodide and its subsequent glycosylation, in order to apply similar conditions to the synthesis of disaccharide 2.…”