It is obtained by condensation of 3,4, 5-trimethoxybenzoyl chloride with & omega;-aminocaproic acid. Dissolve 26.2g (0.2 mol) & omega;-aminoacetic acid in 30 ml of water, neutralize with 12.2g of sodium hydroxide in 30 ml of aqueous solution, and cool to 0-5 ℃. 36 grams (0.15 moles) of 3,4, 5-trimethoxybenzoyl chloride were gradually added under stirring, and the temperature was kept below 5°C. The obtained solution was treated with activated carbon and filtered, and the filtrate was acidified with dilute hydrochloric acid to precipitate. Then filter, wash the cake with water, dry, and recrystallize with hot ethanol to decarbonic acid.