L-Phenylalanine

L-Phenylalanine is an essential aromatic amino acid — (2S)-2-amino-3-phenylpropanoic acid, C9H11NO2, MW 165.19 — that the human body cannot synthesise and must take in from the diet. Its benzyl side chain carries no hydroxyl group, which distinguishes it chemically from L-tyrosine and matters for both formulation and classification. Metabolically it is the substrate of phenylalanine hydroxylase, the enzyme that converts it to L-tyrosine, which in turn is the starting point for the catecholamines dopamine, noradrenaline and adrenaline as well as for melanin and thyroid hormone. That upstream position is why brands place it in mood, focus and daytime-energy formats, and why it appears in medical and parenteral nutrition where a complete essential amino acid profile is required. The largest single industrial outlet is aspartame, the dipeptide methyl ester sweetener built from L-phenylalanine and L-aspartic acid, which is manufactured in thousands of tonnes a year. Modern supply is made by fed-batch fermentation with metabolically engineered Escherichia coli on glucose or glycerol — strains run at commercial titres above 50 g/L in vessels up to 600 m³ — so the material is non-animal, vegan-suitable and free of protein hydrolysate residues. Pharmacopoeial specifications are tight and consistent: USP requires 98.5–101.5% on the dried basis with specific rotation −32.7° to −34.7° at 20 mg/mL in water, loss on drying not more than 0.3%, residue on ignition not more than 0.4%, chloride not more than 0.05%, sulfate not more than 0.03%, iron not more than 30 ppm and pH 5.4–6.0 at 10 mg/mL; Ph. Eur. sets 98.5–101.0% on the dried substance with sulphated ash at most 0.1% and iron at most 10 ppm; FCC limits lead to 5 mg/kg. One regulatory point buyers should build into artwork early: finished foods and drug products containing phenylalanine-releasing ingredients carry a mandatory declaration. US labelling requires "PHENYLKETONURICS: CONTAINS PHENYLALANINE" on aspartame-containing foods and a per-dosage-unit statement on OTC drugs, and Indian FSSAI rules require an equivalent declaration. Thovek ships pharmacopoeial and food-grade L-phenylalanine with a full batch certificate of analysis, elemental impurity and residual solvent data, allergen, GMO and TSE/BSE statements, and Kosher and Halal certification on request.