Chemical Synthesis and the Stability of Theanine

A chemical synthesis procedure for theanine from L-pyrrolidonecarboxylic acid (L-PCA) and ethylamine was modified. L-PCA was allowed to react with excess anhydrous ethylamine (>99%) to produce theanine at 35°C for 10 days. The theanine crystallized from 84% ethanol (V/V) at 4°C with yield of 17-30%. Results shown that L-PCA was conversed into theanine and a 98.2% yield of theanine was obtained by freeze-drying of the reacted mixture directly after reaction in the same manner. The synthesized products were identified by 1H-NMR and MS analysis. Both the isomers existed in products while the L-theanine was dominant. When 10% L-PCA aqueous solution was kept at 4°C for 60 days, about 13% L-PCA decomposed to yield glutamic acid. Since the aqueous solution of ethylamine is a kind of strong base, which may result in decomposed of L-PCA and L-theanine to form glutamic acid. Therefore, the anhydrous ethylamine was used as the substrate. The optimal conditions for theanine crystallization were also discussed.