O(4)-phospho-L-tyrosine is a non-proteinogenic L-alpha-amino acid that is L-tyrosine phosphorylated at the phenolic hydroxy group. It has a role as an Escherichia coli metabolite and an immunogen. It is a L-tyrosine derivative, an O(4)-phosphotyrosine and a non-proteinogenic L-alpha-amino acid. It is a conjugate acid of an O(4)-phosphonato-L-tyrosine(2-). It is an enantiomer of an O(4)-phospho-D-tyrosine.