The cells used comprised normal lung fibroblasts (MRC-5), gastric adenocarcinoma (AGS), leukemia (HL-60), lung cancer (SK-MES-1), and bladder carcinoma (J82). Jatropholone A ( 1) was inactive against all the tumor cell lines; however, its acetylation rendered a compound with antiproliferative activity. The epimeric Jatropholone B ( 8) was active against all the cancer cell lines, and its derivatives presented different effects on the selected cell lines.