According to one kind of synthesis of Shaaban

The present invention provides a method of synthesis of the sand by classes, including [Step 1]: The solvent was the compound (2) was added to a nitrile of the C2-C4, under acidic conditions, the removal of N-Boc protecting group to produce compound (2-a); [step 2]: in step 1 of the reaction solution, first with a tertiary amine, then compound (3) the reaction, after the reaction the reaction solution was treated with lye. The prior literature synthesis method and compared by the method of Shaban, the advantage of mild reaction conditions in each step, high yield, readily available raw materials, simple operation, process stability, etc., and is not used the product purified by column chromatography, just once refined can reach medical requirements. The method of the present invention is therefore more suitable for industrial production.