Aspartame is a methyl ester of the aspartic acid/phenylalanine dipeptide. They cannot synthesize isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Colchicine is biosynthesized from the amino acids phenylalanine and tryptophan. Latter is a dipeptide of phenylalanine and aspartic acid. The amino acids phenylalanine and tyrosine are precursors for catecholamines. Salicylic acid is biosynthesized from the amino acid phenylalanine. Radiolabeling studies identified phenylalanine and valine as the precursors to capsaicin. Amygdalin is a cyanogenic glycoside derived from the aromatic amino acid phenylalanine. It catalyzes the hydrolysis of peptide bonds in L-isomers of tyrosine, phenylalanine, and tryptophan. Tyrosine is synthesized by the hydroxylation of phenylalanine, an essential amino acid. Where they are, the cyanogenic compounds are derived from tyrosine, phenylalanine or leucine. Tyrosine is created from phenylalanine by hydroxylation by the enzyme phenylalanine hydroxylase. A similar attenuation mechanism regulates the synthesis of histidine, phenylalanine and threonine. Mammals synthesize tyrosine from the essential amino acid phenylalanine (phe), which is derived from food. They thereby deduced that the codon UUU specified the amino acid phenylalanine.