L-Phenylalanine-¹³C₆is intended for use as an internal standard for the quantification of phenylalanine by GC- or LC-MS. L-Phenylalanine is an essential amino acid.^1,2,3Blood and brain levels of L-phenylalanine are increased and associated with progressive cognitive impairments, seizures, motor deficits, and autism in patients with phenylketonuria, an inborn error of metabolism characterized by mutations in the gene encoding phenylalanine hydroxylase (PAH). L-Phenylalanine inhibits NMDA-induced currents in primary rat hippocampal neurons (IC₅₀= 1.71 mM).¹It also assembles into fibrilsin vitrothat are cytotoxic to PC12 and CHO cells when used at concentrations ranging from 1.16 to 15 mM.²

1.Glushakov, A.V., Dennis, D.M., Morey, T.E., et al.Specific inhibition of N-methyl-D-aspartate receptor function in rat hippocampal neurons by L-phenylalanine at concentrations observed during phenylketonuriaMol. Psychiatry7(4)359-367(2002) 2.Adler-Abramovich, L., Vaks, L., Carny, O., et al.Phenylalanine assembly into toxic fibrils suggests amyloid etiology in phenylketonuriaNat. Chem. Biol.8(8)701-706(2012) 3.Blau, N., van Spronsen, F.J., and Levy, H.L.PhenylketonuriaLancet376(9750)1417-1427(2010)