Apremilast O-Desmethyl Impurity

N-[2-[(1S)-1-(3-Ethoxy-4-hydroxyphenyl)-2-(methylsulfonyl)ethyl]-2,3-dihydro-1,3-dioxo-1H-isoindol-4-yl]acetamide; 
(S)-N-(2-(1-(3-Ethoxy-4-hydroxyphenyl)-2-(methylsulfonyl)ethyl)-1,3-dioxoisoindolin-4-yl)acetamide;