3-[1-(3-Bromophenyl)-1-hydroxy-n-butyl]benzoic Acid t-Butyl Ester-D9 is the deuterium labelled analogue of 3-[1-(3-Bromophenyl)-1-hydroxy-n-butyl]benzoic Acid t-Butyl Ester (B699930), which is an impurity of Lumacaftor (V900700), which is used in the stabilization of the CFTR protein used in the treatment of cystic fibrosis.