An acyl in the hole: The performance of the serine protease subtilisinCarlsberg (SC) is improved towards transacylation reactions by using secondary alcohols in THF. By enzyme immobilization, the enantioselectivity of SC is increased tenfold. By further protein engineering, an enzyme variant (G165L/M221F) shows increased conversion, enantioselectivity (E>100), substrate scope, and stability in THF