FUT8-IN-1 (Compound 37) is an inhibitor for α-1,6-fucosyltransferase ( FUT8 ) with an K D of 49 nM and an IC 50 of ca. 50 µM. FUT8-IN-1 generates a highly active naphthoquinone imine intermediate in the presence of FUT8 , and inhibits the enzymatic activity of FUT8.