Standardized intermediates: Synthesis of model bacterial O-antigens. A regio-/stereoselective synthesis of 1,2-trans disaccharides as allyl glycosides suitable for chain extension

The synthesis of alpha-L-Rhap-(1-->3)-4-O-Me-alpha-L-Rhap; alpha-L-Rhap-(1-->6)-2,3-di-O-Me-alpha-D-Glcp and beta-D-Glcp-(1-->3)-4-O-Me-alpha-L-Rhap, the three chemically modified spacer armed disaccharide fragments related to bacterial O-lipopolysaccharides (lps) have been reported in the form of allyl glycosides for conjugation to protein. Allyl 4-O-Me-alpha-L-Rhap, allyl 2,3-di-O-Me-alpha-D-Glcp, 2,3,4-tri-O-acetyl-alpha-L-Rhap trichloroacetimidate, 2,3,4-tri-O-acetyl-alpha-L-rhamnopyranosyl chloride and 2,3,4,6-tetra-O-acetyl-alpha-D-Glcp trichloroacetimidate have been used as glycosyl intermediates. Stereoselectivity in the formation of 1,2-trans linked glycosidic bonds is governed by the O-2 acyl group in the glycosyl donor and the regioselectivity leaves margin for further chain extension. Such compounds are expected to be useful in the specificity studies of an antibody raised against related antigen.