The natural product 2'-hydroxycinnamaldehyde (HCA) and its analogue, 2'-benzoyloxycinnamaldehyde (BCA), have been previously shown to have antiproliferative and proapoptotic effects in vitro and inhibit tumor growth in vivo. In this study, we use structure-activity analysis to de. ne structural features that are important for the activity of cinnamaldehyde analogues. Our results emphasize an important role for both the propenal group as well as the modi. cation at the 2'-position. Further studies were aimed to characterize the mechanism of action of BCA. Exposure to BCA induced cell death via caspase-dependent and -independent pathways. Cell death was not due to autophagy or necrosis as a result of energy depletion or induction of reactive oxygen species. Our findings have important implications for future drug design and highlight the importance of de. ning molecular drug targets for this promising class of potential anticancer agents. (C) 2009 Elsevier Inc. All rights reserved.