Process for preparing and purifying a LFA-1 antagonist

It relates to a process for the preparation of lifitegrast (I) by: a) reacting benzofuran-6-carboxylic acid (II) with a non-chlorinated carboxyl activating agent; b) reacting the activated compound of formula (II) obtained in step a) with compound (III) or a salt thereof to give lifitegrast or a salt thereof; and c) optionally isolating the obtained lifitegrast. It also relates to a process for the purification of lifitegrast (I) by i) reacting lifitegrast (I) with dicyclohexylamine to give the dicyclohexylamine salt of lifitegrast (Ia); ii) isolating the compound of formula (Ia) from the reaction medium; iii) converting the dicyclohexylamine salt into lifitegrast by the treatment with an acid; and iv) isolating the compound of formula (I) from the reaction medium. It also relates to dicyclohexylamine salt of lifitegrast and to a process for its preparation.