A series of analogs were synthesized in a straightforward manner from naturally available sesquiterpenes ilicic acid and tessaric acid. The in vitro antiproliferative activities were examined in the human solid tumor cell lines A2780, HBL-100, HeLa, SW1573, T-47D and WiDr. The most potent analog induced considerably growth inhibition in the range 1.9-4.5 microM. Cell cycle studies for tessaric acid derivatives indicated a prominent arrest of the cell cycle at the G(2)/M phase. Damage to the cells was permanent as determine by the so called 24+24 drug schedule.