Efficient Synthesis of p‐Tolyl 6‐Deoxy‐ d ‐Heptopyranose Thioglycosides

Capsular polysaccharides from a range of bacteria, notably campylobacters, possess 6‐deoxy‐heptose residues. Synthetic fragments of these polysaccharides have myriad applications in both fundamental and applied research, but few efficient routes for accessing these monosaccharides in a form suitable for glycosylation reactions are available. The synthesis of thioglycosides of 6‐deoxy‐ d ‐ manno ‐, 6‐deoxy‐ d ‐ talo ‐, and 6‐deoxy‐ d ‐ altro ‐heptoses from a single commercially available and inexpensive monosaccharide, methyl α‐ d ‐mannopyranoside, is reported here. The route involves C‐6 homologation and, in some cases, configurational inversion at C‐3 or C‐4. These routes provide access to glycosyl donors of three of the four naturally occurring 6‐deoxy‐ d ‐heptopyranoses, complementing previous work that has provided glycosyl donors of fourth such monosaccharide, 6‐deoxy‐ d ‐ ido ‐heptopyranose.