Synthesis of the Methyl Glycoside of Ganglioside GM3 Trisaccharide Derivative with N-Acetyl-5-N,4-O-Oxazolidinone Protected p-Toluenethiosialoside

The coupling reaction of N-acetyl-5-N,4-O-oxazolidinone protected p-toluenethiosialoside 1, with four kinds of benzyl or benzoyl protected methyl galactoside diols was deeply studied, which showed a-selectivity with alpha/beta = 1.6 similar to 2.0 and afforded the corresponding sialylation products in high yields (72%similar to 89%). Based on these results, a methyl 2,3,6,2',6'-penta-O-benzyl-beta-lactoside 17 was prepared from lactose with 7 steps in a 19% total yield. Sialylation of compound 17 with donor 1 successfully produced the methyl glycoside ganglioside GM(3) trisaccharide derivative in a 68% yield and alpha/beta = 1.6 : 1.