Studies on chemical modification and biology of a natural product, gambogic acid (II): Synthesis and bioevaluation of gambogellic acid and its derivatives from gambogic acid as antitumor agents

Gambogic acid (GA) has been reported to be a potent Apoptosis Inducer. The fact that it is amenable to chemical modification makes GA an attractive molecule for the development of Anticancer agents. We firstly reported the synthesis of gambogellic acid, which was generated under acid catalysis from readily available GA by a base-catalyzed diene intramolecular annelation. Sequentially, thirteen new compounds were synthesized and their inhibitory activity on HT-29, Bel-7402, BGC-823, and A549 cell lines were evaluated in vitro by MTT assay, and (38, 40)-epoxy-33-chlorogambogellic acid (4) was identified as a BGC-823 cell Apoptosis Inducer through MTT cell assay, observations of morphological changes, and Annexin-V/PI double-staining assay. Compound 4 showed significant effects in inducing Apoptosis and might serve as a potential lead compound for discovery of new Anticancer drugs. Further structure-activity relationships (SARs) of gambogic acid derivatives were discussed.