A series of esters of brusatol, bisbrusatol, and bruceantin were shown to have potent antileukemic activity. Antineoplastic activity was correlated with the ability of the compounds to suppress DNA and protein synthesis in P-388 lymphocytic leukemia cells. Compounds with high T/C% values successfully inhibited DNA polymerase activity and purine synthesis. The ability to inhibit protein synthesis during the elongation process also correlated positively with high antileukemic activity in this series of quassinoids. Dihydrofolate reductase activity and basal and adenosine diphosphate stimulated respiration of P-388 cells were also inhibited.