d-phenylalanine

D-Phenylalanine, a necessary aromatic amino acid, is a precursor of thyroxine, dopamine, melanin, and noradrenaline (norepinephrine).

(S)-2-Hydroxy-3-phenylpropanoic acid (L-(−)-3-Phenyllactic acid) is a chiral aromatic compound involved in phenylalanine metabolism. It is likely produced from phenylpyruvate via lactate dehydrogenase. The D-form is derived from bacterial sources, while the L-form is endogenous. Phenyllactate levels are normally very low in blood or urine, but high levels indicate phenylketonuria (PKU) and hyperphenylalaninemia (HPA). PKU is due to a deficiency of phenylalanine hydroxylase (PAH), causing phenylalanine to convert to phenylpyruvic acid rather than tyrosine.