Sulfated oligosaccharides are a group of compounds with important biological properties as drug molecules. Phosphomannopentaose sulfate (PI-88) is a sulfated oligosaccharide with antitumor properties. PI-88 has been thoroughly investigated as a drug candidate to treat cancers, and it showed promising results in Phase 1 and Phase 2 clinical trials. The glycosidic linkages for the sulfated mannan in PI-88 are mainly of α(1→3) and α(1→2) types. It is important to determine whether the specific glycosidic linkages connecting the sulfated mannan are crucial for the biological activities of PI-88. Therefore, this study explores a method to rapidly synthesize sulfated mannan with α(1→6)linkages. We report here the rapid synthesis of sulfated-α-D-mannopyranan, a PI-88 analogue, by using a regio- and stereocontrolled polymerization of a mannosyl tricyclic orthoester. After the global protecting group removal, the sulfation was successfully carried out by treatment of the unmasked mannans with sulfur trioxide-pyridine complex in dimethyl formamide.
