(S)-1-(3-Ethoxy-4-methoxyphenyl)-2-(methylsulfonyl)ethanamine is a chiral amine derivative featuring a 3-ethoxy-4-methoxyphenyl group and a methylsulfonyl ethylamine side chain. Its structure is characterized by the presence of a sulfonyl group and ether functionalities, making it a valuable synthetic intermediate. This compound is a key chiral intermediate in the synthesis of Apremilast, a phosphodiesterase 4 (PDE4) inhibitor. Apremilast is an active pharmaceutical ingredient (API) used for the treatment of moderate to severe plaque psoriasis and active psoriatic arthritis. The (S)-enantiomer is crucial for the biological activity of the final drug molecule. The synthesis and supply of this high-purity chiral intermediate are critical for the pharmaceutical manufacturing process of Apremilast. Its role underscores the importance of specialized chiral building blocks in the development of modern, targeted therapies for autoimmune and inflammatory diseases.