DZ-/3-PHENYLALANINE

The enzymatic approach for the synthesis of aspartame has the advantage of producing only the (Z,)-a-aspartyl compound (the sweet diastereomer). The less expensive racemic (DZ)-phenylalanine can be used as the starting material. The unreacted (D)-phenylalanine can be recovered and racemized for further reaction. By contrast, the chemical methods used industrially also produce the (L)-p-aspartyl compound (non-sweet) in 10-40% yield, for which a purification step is needed. In 1999, the world market for enzymatically synthesized aspartame was reported to be 800 million US [13]. 

In almost all preparations the hydrazoic acid is dissolved in chloroform or benzene. Since chloroform is completely inert towards hydrazoic add it may be preferable, but imder most conditions benzene is just as satisfactory. Trichloroethylene also has been used successfully as a solvent. The addition of dioxane has been found to be of value in the preparation of dZ-phenylalanine from benzylmalonic acid." Ethyl ether is not a satisfactory solvent, although its use has been mentioned in patents. ... 

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