(1R)-1-(3-ethoxy-4-methoxyphenyl)-2-methylsulfonylethanamine

It serves as the (R)-enantiomer impurity that can be resolved or converted to the required (S)-enantiomer of 1-(3-ethoxy-4-methoxyphenyl)-2-methanesulfonyl-ethylamine, which is then reacted with 3-acetamidophthalic anhydride to produce Apremilast. (1R)-1-(3-ethoxy-4-methoxyphenyl)-2-methylsulfonylethanamine is a chiral intermediate mainly employed to synthesize Apremilast, a medication for psoriatic arthritis.