L-Phenylalanine-15N ((S)-2-Amino-3-phenylpropionic acid-15N) is the 15N-labeled L-Phenylalanine. L-Phenylalanine ((S)-2-Amino-3-phenylpropionic acid) is an essential amino acid isolated from Escherichia coli . L-Phenylalanine is a α2δ subunit of voltage-dependent Ca + channels antagonist with a K i of 980 nM. L-phenylalanine is a competitive antagonist for the glycine- and glutamate-binding sites of N-methyl-D-aspartate receptors (NMDARs) ( K B of 573 μM ) and non-NMDARs , respectively. L-Phenylalanine is widely used in the production of food flavors and pharmaceuticals [1] [2] [3] [4] .