Aspartame is produced by coupling together L-phenylalanine (or L-phenylalanine methyl ester) and L-aspartic acid, either chemically or enzymatically. The former procedure yields both the sweet alpha-aspartame and nonsweet beta-aspartame from which the alpha aspartame has to be separated and purified. The enzymatic process yields only alpha-aspartame.
Production of aspartame normally starts from L-aspartic acid and L-phenylalanine or L-phenylalanine methyl ester. The production follows common routes of peptide synthesis, as the L-configuration of amino acids has to be retained (essential for sweetness). Common production routes require protective groups for aspartic acid. The protective groups commonly used in peptide synthesis have been suggested for aspartame synthesis, but simple protection for large-scale production can be obtained by use of formylaspartic acid anhydride. It can be reacted with phenylalanine methyl ester to N-formylaspartame, from which the protective group has to be removed. Especially simple production is possible from N-formylaspartic acid anhydride and L-phenylalanine. The resulting N-formylaspartylphenylalanine is treated with hydrochloric acid and methanol. The aspartame hydrochloride obtained can be crystallized for purification and transformed into aspartame after addition of a stoichiometric amount of a neutralizing agent. Adjustment of the solvent increases the yield by improving the ratio of alpha- to beta-isomers. Crystallization of alpha-aspartame hydrohalides is a suitable purification step, as beta-hydrohalides are more soluble.
Method for large-scale production of aspartame ... L-aspartic acid anhydride is condensed with L-phenylalanine methyl ester to form a mixture of beta-L-aspartyl-L-phenylalanine methyl ester and alpha-L-aspartyl-L-phenylalanine methyl ester. On acidification with hydrochloric acid, the latter precipitates and the precipitate is neutralized to form aspartame. /From table/
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