Hexahydropyridine-alpha-carboxylic acid, DL-homoproline, piperidicytic acid (Pipecolicacid, referred to as PA), is an important rigid cyclic non-protein amino acid, which can not only define the conformation of polypeptides, but also serve as a multifunctional skeleton in different compound synthesis libraries, so it is widely used in the preparation of many chiral drugs and bioactive substances. For example, the new Chemicalbook local anesthetic Ropivacaine, the antipsychotic drug Thioridazine, the immunosuppressant Rapamycin and the antitumor antibiotic Sandramycin are all prepared with hexahydropyridine-alpha-carboxylic acid or its derivatives as the main raw materials.