Weigh 50g of the by-product (+)1-amino-4-carboxy-2-cyclopentene extracted by γ-lactam enzymatic resolution and put it in a flask, add 200g of water, and slowly add dropwise at 25~30℃ Sulfuric acid, adjust the pH value of the solution to 1~2, after the dripping is completed, add 0.1g of the racemic catalyst o-phthalaldehyde, then heat to reflux, and react for 10~15h. Concentrate under reduced pressure to no fraction, add 200ml of methanol, 20g of tartaric acid, cool to 10-20°C, filter and wash with methanol. Then add 20g of thionyl chloride and 100ml of methanol to the filter cake, react at 65°C for 8h and concentrate under reduced pressure until there is no fraction. Add 100ml of dichloromethane, stir to dissolve and wash the dichloromethane layer twice with drinking water to obtain (- ) Methyl 1-amino-4-carboxylate-2-cyclopentene in dichloromethane solution, yield 42%.