The invention discloses a method for preparing
spermidine. The method comprises the following steps: dissolving
oxalyl chloride and a base in a first
solvent, slowly adding 4-bromo-1-
butylamine hydrobromic acid, and reacting to obtain 2-((4-bromobutyl)amino)-2-oxoacetyl
chloride; adding a base to the reaction
solvent of the obtained 2-((4-bromobutyl)amino)-2-oxoacetyl
chloride, and slowly adding 3-bromo-1-
propylamine hydrobromic acid to obtain N 1 ‑(4‑Bromobutyl)‑N 2 ‑(3‑bromopropyl)oxalamide; 1 ‑(4‑Bromobutyl)‑N 2 ‑(3‑bromopropyl)oxalamide,
benzylamine and a base are added to a second
solvent to react to obtain 8‑benzyl‑1,4,8‑triazacyclododecane‑2,3‑dione; 8‑benzyl‑1,4,8‑triazacyclododecane‑2,3‑dione is added to an acid for
hydrolysis to obtain N 1 ‑(3‑Aminopropyl)‑N 1 Benzylbutane-1,4-
diamine; N 1 ‑(3‑Aminopropyl)‑N 1 Benzylbutane-1,4-
diamine is added to
Raney nickel /
methanol, and
hydrogen is passed through the reaction to obtain crude
spermidine, which is then distilled to obtain pure
spermidine. The preparation method of the present invention is easy to operate and safe, easy to industrial-scale production, and has a high conversion rate of spermidine and high product purity.