Preparative method of dihydrocucurbitacin f-25-o-acetate and the use thereof in the manufacture of medicaments for treating cancers

A preparation method of curcurbitacin IIa, comprising the following steps:

• a, the tuber of Hemsleya amalils Diels plant is obtained and comminuted, then extracted by a percolation method, using acetone of 18-26 weight times as solvent, then the extractant is recycled in water bathe of 60-70° C. for extract paste;
• b. the obtained extract paste is mixed with silica gel of 1-2 weight times, then dried and subjected to the silica gel column, then gradient eluted by a mixed solvent comprising chloroform and methanol, wherein a volume concentration of the methanol is 2-10%, then the eluent is recycled and crude product is obtained;
• c. the crude product is heated and dissolved in a water bath using methanol or ethanol, then the obtained solution is filtered and placed in a room temperature for recrystallization, then the obtained prismy crystals is the curcurbitacin IIa of 98% purity.