Due to the failure of using 3,5,7,20-O-tetraacetylsilybin as precursor for the selective esterification, free silybin, without any protection was used as starting material. As reported by Li and Decker , under Mitsunobu conditions, a regioselective 23-OH esterification of silybin moiety was formed preferentially. However, in our case the esterification did not occur when using Mitsunobu conditions (DEAD/PPh3 or DIEA/PPh3).