Abstract
An efficient synthesis of the protected branched trisaccharide (2′S,3′S)‐(7‐O‐benzyl‐6‐O‐chloroacetyl‐3,4‐O‐(2′,3′‐dimethoxybutane‐2′,3′‐diyl)‐2‐O‐p‐methoxybenzyl‐L‐glycero‐α‐D‐manno‐heptopyranosyl)‐(1 → 3)‐[(2,3,4,6‐tetra‐O‐benzoyl‐β‐D‐glucopyranosyl)‐(1 → 4)]‐7‐O‐acetyl‐1,6‐anhydro‐2‐O‐benzyl‐L‐glycero‐β‐D‐manno‐heptopyranose, which is a key intermediate in the synthesis of inner core structures of Haemophilus and Neisseria LPSs, is described. The heptoses were formed by Grignard reactions using a benzyloxymethyl chloride or a commercial vinyl reagent. The anhydro bridge was formed by treatment of a 6‐OH methyl α‐heptoside precursor with FeCl3. The protecting group pattern allows modifications at the 2‐, 3‐, 4‐, and 6‐positions of the second heptose moiety and also, after acetolysis of the anhydro bridge, elongation at the reducing end, all known alterations found in the bacterial LPSs.
Acknowledgements
Financial support from the Swedish Science Research Council is gratefully acknowledged.