Synthetic method of double-sialylated tetrasaccharide

The invention discloses a synthetic method of synthesizing double-sialylated tetrasaccharide by a chemically controllable enzyme method. The invention further provides two intermediates, which are used for synthesizing and preparing the double-sialylated tetrasaccharide, are compounds respectively as shown in formulas IV and V. According to the synthetic method disclosed by the invention, the flexibility of a chemical synthetic method and the high-area selectivity and high efficiency of the enzyme synthetic method are combined together, so that synthesis of the double-sialylated tetrasaccharide by using a chemical intervention method is firstly realized, defects such as low substrate reaction activity, multiple synthetic steps and low yield facing in existing chemical synthesis of the double-sialylated tetrasaccharide are solved, as well as a problem that sialyl transferase is difficult to obtain and only glycopeptides is identified in the enzyme method is solved; the synthetic method disclosed by the invention has the advantages of high substrate reaction activity and high yield, and therefore, the synthetic method has important significance in researching biological functions of sialic acid glucoside on molecular level and developing carbohydrate drugs based on the biological functions.