A series of sulfonium salts derived from 1,5-dithiopent-1-enopyranosides was prepared in a three-step sequence from protected D- and L-erythrofuranoses. The key step is the nucleophilic displacement of a leaving group by a sulfur atom of carbohydrate-derived ketene dithioacetals. Such compounds were assayed for their properties as glycosidase inhibitors. (C) 2009 Elsevier Ltd. All rights reserved.