Relative to theanine, the opposite ( D-, R-) enantiomer is largely absent from the literature, except implicitly. Theanine is a derivative of glutamine that is ethylated on the amide nitrogen (as the name N 5-ethyl- L-glutamine describes), or alternatively, to the amide formed from ethylamine and L-glutamic acid at its γ- (5-) side chain carboxylic acid group (as the name γ-L-glutamylethylamide describes).
Theanine is an analog of this amino acid, and its primary amide, L- glutamine (also a proteinogenic amino acid). The name theanine, without prefix, is generally understood to imply the L- ( S-) enantiomer, derived from the related proteinogenic L-amino acid glutamic acid. The chemical name N 5-ethyl- L-glutamine and other synonyms (see box) for theanine reflect its chemical structure. Therefore, health claims for L-theanine are not recognized in the European Union. In 2011, the European Food Safety Authority concluded that a cause and effect relationship had not been established between consumption of L-theanine and improved cognitive function, alleviation of psychological stress, maintenance of normal sleep, or reduction of menstrual discomfort. The German Federal Institute for Risk Assessment, an agency of their Federal Ministry of Food and Agriculture, objects to the addition of L-theanine to beverages. In the United States, the Food and Drug Administration (FDA) considers it to be generally recognized as safe (GRAS) and allows its use as an ingredient in dietary supplements or foods up to a maximum of 250 mg per serving. In Japan, L-theanine has been approved for use in all foods, with some restrictions in the case of infant foods. The regulatory status of theanine varies by country. The opposite enantiomer, D-theanine, has been studied less. The name theanine without a prefix generally implies the enantiomer, L-theanine, which is the form found in tea leaves and as a dietary supplement ingredient. Theanine provides a unique brothy or savory ( umami) flavor to green tea infusions. It was discovered as a constituent of green tea in 1949 in 1950, it was isolated from gyokuro leaves. Theanine / ˈ θ iː ən iː n/, also known as L-γ-glutamylethylamide and N 5-ethyl- L-glutamine, is an amino acid analogue of the proteinogenic amino acids L-glutamate and L-glutamine and is found primarily in particular plant and fungal species.
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