The fluorescence-labeled hexasaccharide (Glc alpha 1-2Glc alpha 1-3Glc alpha 1-3Man alpha 1-2Man alpha 1-2Man alpha) was synthesized as a substrate for the processing enzyme alpha-glucosidase I. To construct the 1,2-cis glucosidic linkages, we employed an alpha stereoselective coupling using the mannosyl donor by assisted neighboring-group participation, followed by conversion of the stereochemistry of the C-2 hydroxyl group in the mannose residue using sequential oxidation of C-2 hydroxyl group to a 2-keto group and stereoselective reduction of the hydroxyl group to the gluco-configuration to provide the corresponding alpha-glucoside derivative. Using this strategy, the three consecutive alpha-glucosidic linkages were easily obtained in a stereoselective manner. Finally, the Dansyl labeled hexasaccharide derivative was used to measure the activity of processing alpha-glucosidase I. (c) 2012 Elsevier Ltd. All rights reserved.