?Montelukast EP Impurity C ; Montelukast USP Related Compound A ; Montelukast Sulfoxide ; Montelukast S-Oxide ; [1-[[[1-[3-[(E)-2-(7-chloroquinolin-2-yl)ethenyl]phenyl]-3-[2-(2-hydrox-ypropan-2-yl)phenyl]propyl]sulfinyl]methyl]cyclopropyl]acetic acid.