L-Phenyl-d5-alanine-2,3,3-d3 is an isotope labelled compound of L-Phenylalanine (P319415). L-Phenylalanine (Aspartame EP Impurity C) is an essential amino acid. L-Phenylalanine is biologically converted into L-tyrosine, another one of the DNA-encoded amino acids, which in turn is converted to L-DOPA and further converted into dopamine, norepinephrine, and epinephrine. L-Phenylalanine is produced for medical, feed, and nutritional applications such as in the preparation of Aspartame. Neuroprotective product.