A mixture of 2-S-(2,3,4,6-tetra-O-acetyl-α-D-mannopyranosyl)-2-thiopseudourea hydrobromide (1) (90 g, 0.185 mol), freshly crystallized 3-iodopropionic acid (37 g, 0.199 mol), potassium carbonate (29.6 g, 0.215 mol), and potassium metabisulfite (37 g, 0.167 mol) in acetone (150 ml) and water (150 ml) is stirred for 45 minutes at room temperature. Hydrochloric acid (5%, 700 ml) and chloroform (700 ml) are added to the mixture. The organic layer is separated and washed with water, dried, and evaporated in vacuo to an oil (80 g, quantitative yield) that is used, without further purification, for the preparation of 3.
