(βS)-rel-Ethyl N-(Diphenylmethylene)-3-(phenylmethoxy)-O-(phenylmethyl)-β-[(trimethylsilyl)oxy]-D-tyrosine Ester-D3 is an intermediate used in the synthesis of DL-threo-Droxidopa-d3 (D689953), which is an isotope labelled compound of DL-threo-Droxidopa (D689950), a synthetic amino acid precursor of Norepinephrine. An antiparkinson.