(S,E)-1-(3-(2-(7-Chloroquinolin-2-yl)vinyl)phenyl)-3-(2-(2-hydroxypropan-2-yl)phenyl)propyl-d6 Methanesulfonate is an intermediate in synthesizing Montelukast-d6 (M568004), is the labeled analogue of Montelukast (M568000), a selective leukotriene D4-receptor antagonist. Used as an antiasthmatic.