Improved synthetic process of apremilast

To optimize the process of hydrogenation reduction in the synthesis of apremilast (APST), 3-nitrophthalic anhydride (4) and (S)-1-(3-ethoxy-4-methoxyphenyl)-2-(methylsulfonyl) ethanamine-(S)-2-acetamido-4-methylpentanoate (7) were used as starting materials to synthesize (S)-2-(1-(3-ethoxy-4-methoxyphenyl)-2-(methylsulfonyl)ethyl)-4-nitroisoindoline-1,3-dione (8) by amination.Then compound 8 was reduced to (S)-4-amino-2-(1-(3-ethoxy-4-methoxyphenyl)-2-(methylsulfonyl) ethyl) isoindoline-1,3-dione (9) with ammonium formate as hydrogen source and palladium hydroxide as catalyst.Finally, apremilast was obtained by the acetylation reaction with acetic anhydride.The structure of the products were verified by optical rotation, ¹H NMR, ¹³C NMR, MS and elemental analysis.And the total yield of three steps was increased to 67.0%.The improved reduction process can avoid the special reaction of hydrogenation and pressurization, and reduce the safety risk and production costs with high commercial value.