L-Theanine

L‑Theanine (γ‑ethylamino‑L‑glutamic acid) is a non‑proteinogenic amino acid most abundant in the leaves of Camellia sinensis (tea) and in certain mushroom species. It is primarily valued for its ability to modulate brain activity, promoting a state of relaxed alertness without sedation, which makes it a popular nutraceutical for stress‑reduction and cognitive support.

L‑Theanine is the N‑ethyl derivative of the amino acid glutamine.

• Its IUPAC name is (2S)-2‑amino‑5‑(ethylamino)pentanoic acid.
• Molecular formula: C₇H₁₄N₂O₃; molecular weight: 174.20 g/mol.
• It exists as a single stereoisomer (L‑form) with a chiral center at the α‑carbon (S‑configuration).
• The structure comprises a central α‑amino acid backbone (–CH(NH₂)–COOH) with an ethyl‑substituted side‑chain amide (–CH₂CH₃–NH–) attached to the γ‑ carbon, giving it both hydrophilic (carboxyl, amine) and moderate lipophilic (ethyl) characteristics.
• L‑theanine is water‑soluble (≈30 g/L at 25 °C) and relatively stable across pH 4–8.
• Its chemical stability makes it amenable to standard aqueous extraction from tea leaves or microbial fermentation, and it can be chemically synthesized via ethylation of L‑glutamine under controlled conditions.

The primary natural source of L‑theanine is the leaf of the tea plant (Camellia sinensis), where it accounts for 1–3 % of dry leaf weight.

• Commercially, L‑theanine is extracted using hot water or ethanol extraction, followed by purification via crystallization or chromatography to achieve >95 % purity.
• An alternative, increasingly common, method is microbial fermentation (e.g., Bacillus subtilis or Corynebacterium glutamicum engineered to produce L‑theanine from glutamate) which yields a product identical to plant‑derived L‑theanine but with higher batch consistency.
• Quality‑focused manufacturers verify identity and purity with HPLC, provide certificates of analysis (COA), and test for heavy metals, pesticide residues, and microbial contamination.
• For the highest quality supplement, choose products that are GMP‑certified, third‑party tested (e.g., NSF, USP), and label the source (e.g., “fermented L‑theanine, 99 %+ purity”).