What Is L-Theanine?

L-theanine is a naturally occurring, non-protein amino acid found in the leaves of Camellia sinensis, the plant from which tea is produced. It was first isolated and identified in 1949 by Japanese researcher Yajiro Sakato and described in a publication accepted that year and published in 1950.

(Source: PubChem CID 439378 — L-Theanine Compound Summary) (Source: Sakato Y — Isolation of Theanine from Gyokuro Tea, Journal of the Agricultural Chemical Society of Japan, 1950)

Chemical Identity

L-theanine is classified as a non-protein amino acid. It is structurally related to glutamine and is sometimes described as a glutamine analogue. The naturally occurring form is the L-enantiomer, which is reflected in the compound's name.

Accepted IUPAC Name	(2S)-2-amino-5-(ethylamino)-5-oxopentanoic acid
Molecular Formula	C₇H₁₄N₂O₃
Molecular Weight	174.20 g/mol
CAS Registry Number	3081-61-6
Classification	Non-protein amino acid; glutamine analogue
Stereochemistry	L-enantiomer

(Source: PubChem CID 439378 — L-Theanine Compound Summary) (Source: DrugBank DB04464 — Theanine)

Where L-Theanine Occurs Naturally

L-theanine occurs naturally in the leaves of Camellia sinensis. It is the predominant free amino acid found in tea leaves. Measured concentrations vary depending on leaf maturity, growing conditions, and harvest timing — young leaves and apical buds have been reported to contain higher concentrations, while older and more mature leaves contain lower amounts.

(Source: PubMed PMID 28605204 — Occurrence, Biological Activities and Safety of Theanine) (Source: PubMed PMID 18296328 — L-Theanine, a Natural Constituent in Tea, and Its Effect on Mental State)

L-Theanine in the Plant

Within Camellia sinensis, L-theanine biosynthesis is strongly associated with root tissue. Research has demonstrated that biosynthesis can occur in multiple plant tissues, and the roots are the primary documented site rather than the exclusive one.

From the roots, L-theanine is distributed through the plant via the xylem, traveling to developing above-ground tissues. This transport pattern is consistent with the observed accumulation of L-theanine in young leaves and apical buds, and its decline in older, more mature leaves.

(Source: Takeo T — Biosynthesis of Theanine in Tea Plants, Phytochemistry, 1974) (Source: PubMed PMID 28605204 — Occurrence, Biological Activities and Safety of Theanine)

How L-Theanine Can Be Produced

L-theanine can be obtained from Camellia sinensis leaves through extraction from plant material. It can also be produced through controlled enzymatic synthesis.

(Source: PubChem CID 439378 — L-Theanine Compound Summary) (Source: USP Food Chemicals Codex — L-Theanine)

Discovery and History

L-theanine was first isolated and identified by Yajiro Sakato, a Japanese researcher, from Gyokuro green tea leaves (Camellia sinensis). Sakato's work was accepted in 1949 and published in 1950 in the Journal of the Agricultural Chemical Society of Japan. His analysis identified L-theanine as a previously unknown amino acid constituent of tea — a compound that had not been characterized before that investigation.

(Source: Sakato Y — Isolation of Theanine from Gyokuro Tea, Journal of the Agricultural Chemical Society of Japan, 1950)

L-Theanine Quick Facts

Classification	Non-protein amino acid
Molecular Formula	C₇H₁₄N₂O₃
Molecular Weight	174.20 g/mol
CAS Number	3081-61-6
Primary Natural Source	Camellia sinensis leaves
Predominant Free Amino Acid In	Tea leaves (Camellia sinensis)
First Isolated	1949/1950 — Yajiro Sakato, Japan
PubChem CID	439378

Frequently Asked Questions

What type of compound is L-theanine?

L-theanine is a non-protein amino acid. It is structurally related to the amino acid glutamine and is classified as a glutamine analogue. It is not incorporated into proteins in the same way that standard dietary amino acids are.