Synthesis of the tetrasaccharide core region of antigenic lipo-oligosaccharides characteristic of mycobacterium kansasii

The oligosaccharide core region, β- d-Glc p-(1→3)-β- d-Glc p-(1→4)-α- d-Glc p-(1↔1)-α- d-Glc p ( 1), of the lipo-oligosaccharide-type antigens isolated from M. kansasii has been synthesised from 2,3,2′,3′,4′,6′-hexa- O-benzyl-6- O-(1-phenylethyl)-α,α-trehalose ( 4). Compound 4 was obtained by LiAlH 4-AlCl 3-type hydrogenolysis of 2,3,2′,3′,4′,6′-hexa- O-benzyl-4,6- O-( S)-(1-phenylethylidene)-α,α-trehalose. The β-laminaribiosyl part of the molecule was built-up by sequential glycosylation steps using 2,4,6-tri- O-acetyl-3- O-allyl-α- d-glucopyranosyl bromide in the presence of HgBr 2 and methyl 2,3,4,6-tetra- O-acetyl-1-thio-β- d-glucopyranoside promoted by methyl triflate. The complete a priori 13C-n.m.r. spectrum assignment of 1 was achieved by applying 2D methods.