Synthesis of methyl pyranosides and furanosides of 3-deoxy- d- manno-oct-2-ulosonic acid (KDO) by acid-catalysed solvolysis of the acetylated derivatives

Abstract

Treatment of methyl 2,4,5,7,8-penta- O-acetyl-3-deoxy-α- d- manno-oct-2-ulopyranosonic acid, or its methyl ester, with refluxing methanolic 0.1 m hydrogen chloride for 16 h gave 95% of methyl (methyl 3-deoxy-α- d- manno-oct-2-ulopyranosid)onate. Acetylation of the methyl ester of 3-deoxy- d- manno-oct-2-ulosonic acid (KDO) gave mainly methyl 2,4,6,7,8-penta- O-acetyl-3-deoxy-α,β- d- manno-oct-2-ulofuranosonate. Treatment of this mixture with methanolic 0.02 m hydrogen chloride at room temperature gave methyl (methyl 3-deoxy-α,β- d- manno-oct-2-ulofuranosid)onate and the corresponding 4-acetates which were isolated by reverse-phase column chromatography of their 7,8- O-isopropylidene derivatives. Confirmation of the position of the isopropylidene group was obtained by acetylation to give methyl (methyl 4,6-di- O-acetyl-3-deoxy-7,8- O-isopropylidene-α,β- d- manno-oct-2-ulofuranosid)onate. The furanose anomers were differentiated primarily by J 3,4 values (α ∼6.1 Hz, β ∼2.2 Hz). The anomeric configuration in the furanose series has been assigned on the basis of optical rotation.