N-Fmoc-(13C9,15N)-L-Tyrosine O-Tertbutyl Ether is the isotope labelled protected form of L-Tyrosine (T899975), an essential amino acid that exhibits in vitro antioxidant and antiradical activities. L-Tyrosine is used as a precursor to synthesize catecholamines (e.g. Norepinephrine HCl [N674500]) in human keratinocytes, and also for the synthesis of proteins and thyroid hormones.