Gambogic acid （GA, 1）, the most prominent representative of Garcinia natural products, has been reported to be a promising anti-tumor agent. In order to further explore the structure-activity relationship of GA and discover novel GA derivatives as anti-tumor agents, 17 novel C-37 modified derivatives of GA were synthesized and evaluated for their in vitro anti-tumor activities against A549, HCT-116, BGC-823, HepG2 and MCF-7 cancer cell lines. Among them, 11 compounds were found to be more potent than GA against some cancer cell lines. Notably, com- pound 8 was almost 5--10 folds more active than GA against A549 and BGC-823 cell lines with the IC50 values of 0.12 μmol·L^-1 and 0.57 μmol·L^-1, respectively. Chemical modification at C-37 position of GA by introducing of hydrophilic amines could lead to increased activity and improved drug-like properties. These findings will enhance our understanding of the structure-activity relationship （SAR） of GA and lead to the discovery of novel GA derivatives as potential anti-tumor agents.
