Synthesis and evaluation of caged Garcinia xanthones

Inspired by the combination of unique structure and potent bioactivities exhibited by several family members of the caged Garcinia xanthones, we developed a synthesis of simplified analogues that maintain the overall caged motif. The caged structure of these compounds was constructed via a site-selective Claisen/Diels-Alder reaction cascade. We found that the fully substituted caged structure, in which are included the C18 and C23 geminal methyl groups, is necessary to maintain bioactivity. Analogue 17 had comparable activity to the natural products of this family, such as gambogic acid. These compounds exhibit cytotoxicity in a variety of tumor cell lines at low micromolar concentrations and were found to induce apoptosis in HUVE cells. In addition, studies with HL-60 and HL-60/ADR cells indicate that these compounds are not affected by the mechanisms of multidrug resistance, conferred by P glycoprotein expression, typical of relapsed cancers and thus represent a new and potent pharmacophore.