Aspartame through Enzymatic Peptide Synthesis

Aspartame is a dipeptide ester, a-L-aspartyl-L-phenylalanine-OMe, 200 times as sweet as sucrose. Aspartame is utilized by now as a low-calorie sweetener in soft drinks, salad dressings, ready-made meals, table-top sweeteners, and pharmaceuticals, and had reached a market volume of 12000-15000 ha. One of the most successful and interesting syntheses is the Toyo Soda enzymatic process which runs on an industrial scale in a joint venture with DSM (Dutch State Mines, Geleen, NL). 

Formation of the peptide bond is catalyzed by thermolysin, a neutral zinc protease (Fig. 4-7). The enzyme employed was found in the bacterial strain Bacillus proteo-licus/thermoproteolyticus in the Rokko Hot Spring in Japan. The enzyme is stable up to temperatures of 60 °C. It is extracted and used in a form soluble in water. In this process the amino acids phenylalanine and asp artic acid are coupled by the enz5Tne. The process, including the main steps, is shown schematically in Fig. 4-7. 

The reaction is limited by the equilibrium position, and so products have to be removed from the mixture in order to a chieve high yields. In excess of phenylalanine methyl ester the protected aspartame forms a poorly soluble carboxylate anion which precipitates from the reaction mixture. This makes it easy to remove by fihra tion. The last step of the process is the removal of protecting group by conventional 

The enzyme is completely stereo selective, this means that it is possible to use either a racemic mixture or the L-isomer of the substrate. 

The reaction takes place under mUd conditions (pH 7.0-7.5, temperamre 50 °C, in aqueous solution). 

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Aspartame , Artificial Sweetener through Enzymatic Peptide Synthesis... 

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