Multigram-scale synthesis of l,d-heptoside using a Fleming-Tamao oxidation promoted by mercuric trifluoroacetate

• Heptosides are important bacterial carbohydrates associated with key cellular functions.
• Heptosides are involved in the pathogenicity and the virulence of some important infectious agents.
• Multi-gram scale synthesis of L,D-mannoheptose, a key component of Lipopolysaccharide.
• Clickable heptosides as interesting molecular tools for generating libraries of heptose mimetics.
• Heptose glycomimetics.

An efficient multigram-scale synthesis of methyl 2,3,4,6-tetra-O-benzyl-l-glycero-α-d-manno-heptopyranoside from methyl 2,3,4-tri-O-benzyl-α-d-mannopyranoside is reported. It involves a sequence of Swern oxidation, Grignard addition and Fleming-Tamao reactions. The resulting scaffold was used as a precursor to design a small library of clickable l-heptosides. This study shows that the use of mercuric bistrifluoroacetate is required both to accelerate and to cleanly perform the Fleming-Tamao oxidation, without side-reactions.

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