D-galacturonic acid derivatives as acceptors and donors in glycosylation reactions

Jones oxidation of suitably protected allyl beta-D-galactopyranosides and subsequent esterification were reinvestigated. Partial deprotection of the resulting D-galacturonic acid derivatives afforded compounds suitable for transformation into glycosyl acceptors. The synthesis of 2-, 3-, and 4-trityl ethers, relying on efficient differential protecting-group strategies, is described. Trityl-cyanoethylidene condensation of these trityl ethers, leading to the protected disaccharide units beta-D-GalpA-(1-->2)-D-GalpA and beta-D-GalpA-(1-->3)-GalpA with high stereoselectivity, is demonstrated. A beta-D-GalpA-(1-->4)-D-GalpA disaccharide was also prepared.