Notably , compound 7a exhibited potent anti - proliferative activity against HepG2 cells with the half maximal inhibitory concentration ( IC 50 ) value of 4 . 95 [UNK] , which was enhanced 8 . 8 - fold compared to the parent compound emodin ( IC 50 = 43 . 87 [UNK] ) , and it also exhibited better selective anti - proliferative activity and specificity than emodin .