Abstract: Using DL-phenylalanine methyl ester as reaction substrate instead of L-phenylalanine methyl ester, aspartame was synthesized in good yield by the catalysis of either thermolysin or the immobilized thermolysin.In addition, optical resolution of DL-phenylalanine methyl ester could be achieved simultaneously in this reaction process.Costly D-phenylalanine methyl ester was also obtained in high yield.In the enzymatic reaction, the effects of reaction conditions on the synthetic yield were studied.Reuse of the immobilized thermolysin was also investigated.The experimental results showed that the immobilized thermolysin has better reuse ability.In comparison with the reaction catalyzed by thermolysin, the reaction catalyzed by the immobilized thermolysin required a longer time, and tile yield is slightly lower.The present work provided an economic and practical method for the preparation of aspartame.

Key words: Thermolysin, Aspartame, Immobilized enzyme, Enzymatic synthesis, Optical resolution