Chemical synthesis is a method to produce or prepare amino acids by combining organic synthesis with chemical engineering. The chemical synthesis of DL tryptophan can be roughly divided into two kinds: the synthesis with indole as raw material and the synthesis with phenylhydrazine as raw material. Snydcr and MacDonald developed a simple method for the synthesis of DL tryptophan, that is, using indole and acetic anhydride in the presence of acetic acid and acetic anhydride α- N-ethylphthalide-DL-tryptophan is obtained by direct condensation of acetylaminoacrylic acid, which can be hydrolyzed in sodium hydroxide solution to obtain DL tryptophan in 57.7% yield. Moe and MacDonald reported that tryptophan was synthesized from phenylhydrazine, that is, in the presence of sodium acetate, acrolein and diethyl acetaminomalonate were condensed, and the condensate reacted with phenylhydrazine to generate phenylhydrazone. The phenylhydrazone was hydrolyzed in H2S04 or BF3 aqueous solution under reflux, and cyclized to obtain the compound 3-indolyl-methyl-acetylaminomalonate diethyl ester. The compound was hydrolyzed and decarboxylated to obtain DL tryptophan.
The greatest advantage of chemical synthesis is that it is not limited in the variety of amino acids. It can not only prepare natural amino acids, but also prepare various unnatural amino acids with special structures. However, this does not mean that it has industrial production value. Since the amino acids synthesized are DL type racemates, they must be separated to obtain L-amino acids that can be used by human body. Therefore, when DL tryptophan is produced by chemical synthesis, in addition to the synthetic process conditions, the resolution of isomers and racemic utilization of D-tryptophan isomers should also be considered. Therefore, the application of chemical synthesis of L-tryptophan in industry is also limited.