The Chemical Synthesis And Basic Properties Of L-theanine

As a new kind of natural food additive and a special amino acid in tea, L-theanine was approved in 1985 by FDA, and affirmed that L-theanine was GRAS (generally recognized as safety).When it is used, there is no restrictiveness in amount. Besides, it possesses many functions, which are useful to us. A review with summation in preface was given on the research progress of L-theanine in its natural resources, physiological functions, preparation, examination and applications.In order to overcome the shortcomings of chemical synthesis of L-theanine that it takes long time and reacts in high pressure, pyridine, secondary propyl alcohol, ethanol absolute and water were chose as solvent system principally from the point of view of reactants' solubility. Ethylamine anhydrous and L-pyroglutamic acid reacted in different homogeneous systems, and the dynamics were studied respectively. The results indicated that ethylamine anhydrous and L-pyroglutamic acid reacted in pyridine, reaction time 52 hours, the consistency of L-pyroglutamic acid 25g/100ml, mixture ratio 4:1 (mole ratio of ethylamine anhydrous and L-pyroglutamic acid), the yield and purity of theanine reached to 21.2% (counted by L-pyroglutamic acid ) and 98.2% respectively, under such conditions, the reaction time was the shortest, and the yield was the highest.The product of synthetic L-theanine was studied by Infrared Spectra, physical and chemical methods, and the results showed that the product' properties were similar with standard product. The purity of L-theanine were determined by titration in non-aqueous solvent and rotatory method, the results showed that the purity upwards of 98%.Based on the amino acid structure of L-theanine and the research progress of amino acid complexes, the coordinating properties of L-theanine, L-glutamic acid and L-pyroglutamic acid were studied. Judging whether they could coordinate with different metal ions by UV and pH potentiometic method, the mixes and stability constants were determined by spectrophotometer. The results showed that the coordinating properties as follows: L-glutamic acid >L-theanine > L-pyroglutamic acid,Hg²⁺> Cu²⁺ > Ni²⁺ > Cr3+ > Co²⁺ > Zn²⁺.