This compound is the L-leucine, N-acetyl salt of (S)-1-(3-ethoxy-4-methoxyphenyl)-2-(methylsulfonyl)ethanamine. It is a key intermediate in the synthesis of apremilast, a phosphodiesterase 4 (PDE4) inhibitor. Apremilast is an active pharmaceutical ingredient (API) approved for the treatment of moderate to severe plaque psoriasis and active psoriatic arthritis. The (S)-enantiomer of the free base amine is crucial for the biological activity of apremilast. This specific salt form, with N-acetyl-L-leucine as the counterion, is often employed to improve the physicochemical properties, such as crystallinity, stability, and solubility, of the amine intermediate during the manufacturing process. Its primary industrial application is strictly within the pharmaceutical supply chain for the production of the final drug substance. Handling requires standard laboratory precautions for fine chemicals. As a pharmaceutical intermediate, it is not intended for direct therapeutic use and is supplied for research and development purposes or for use in regulated API synthesis under current Good Manufacturing Practice (cGMP) conditions.