An aromatic nonpolar amino acid with the formula C6
)COOH. The biosynthetic pathway (see shikimic acid
) to phenylalanine from erythrose 4-phosphate and phosphoenolpyruvate is similar for all the aromatic amino acids. Phenylalanine and the other aromatic amino acids are precursors of a large number of aromatic compounds, mostly found only in plants. Deamination of phenylalanine yields cinnamic acid, important in the synthesis of lignin. Phenylalanine is also a precursor of such alkaloids as morphine and curare (i.e. the isoquinoline alkaloids).