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-a-D-manno-heptopyranosyl)-(1->3)-[(2,3,4,6-tetra-O-benzoyl-b-D-glucopyranosyl)-(1->4)]-7-O-acetyl-1,6-anhydro-2-O-benzyl-L-glycero-b-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 com. vinyl reagent. The anhydro bridge was formed by treatment of a 6-OH Me a-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. [on SciFinder (R)]