N,N'-[1,2-Ethanediylbis[oxy[5-(2-methoxyphenoxy)[2,2'-bipyrimidine]-6,4-diyl]]]bis[4-(1,1-dimethylethyl)-benzenesulfonamide-d4 is labelled N,N'-[1,2-Ethanediylbis[oxy[5-(2-methoxyphenoxy)[2,2'-bipyrimidine]-6,4-diyl]]]bis[4-(1,1-dimethylethyl)-benzenesulfonamide (E676300) which is an impurity of Bosentan (B675900), a mixed endothelin receptor antagonist.