Different pathways for the deoxygenation of the A-ring of natural triterpene compounds

Semisynthesis of SY-1 for investigation of breast cancer stem cell selectivity of C-ring-modified salinomycin analogues

Salinomycin, a naturally occurring polyether ionophore was recently found to selectively reduce the proportion of CD44(+)/CD24(-) cells, a phenotype associated with breast cancer stem cells. Subsequent studies from our group showed that chemical modification of the allylic C20 hydroxyl of salinomycin, located at the C-ring, can enhance the activity of derivatives against breast cancer cells over 5-fold compared to the native structure. Access to C-ring-modified salinomycin analogues is thus of interest from both a mechanistic and a synthetic perspective. Here, we report efficient strategies for gram scale synthesis of the natural product SY-1 (20-deoxy salinomycin), and a saturated analogue, 18,19-dihydro SY-1, for a comparative in vitro investigation of the biological profiles of these compounds with that of salinomycin. Across several assays, the deoxygenated structures required higher concentrations to elicit similar cellular responses to that of salinomycin. Similarly to salinomycin, SY-1 or 18,19-dihydro SY-1 treatment was found to reduce the proportion of CD44(+)/CD24(-) cells with essentially complete selectivity up to ∼IC25. Importantly, the proportion of CD44(+)/CD24(-) cells showed a pronounced U-shaped dose response curve for salinomycin and its derivatives, but not for paclitaxel. The concentration for maximum response in this assay followed differences in IC50 for salinomycin and its analogues, which emphasizes the importance of taking concentration dependence into account when comparing effects on the CD44(+)/CD24(-) phenotype. Small differences in the global conformation within the triad of compounds investigated together with differences in activity across assays emphasize the importance of substitution at C20 for the activity of salinomycin and its derivatives.

Synthesis and biological evaluation of oleanolic acid derivative–chalcone conjugates as α-glucosidase inhibitors

Series of oleanolic acid derivative–chalcone conjugates were designed, synthesized and their α-glucosidase inhibitory activities were investigatedin vitro.

Esters and amides of maslinic acid trigger apoptosis in human tumor cells and alter their mode of action with respect to the substitution pattern at C-28

Cancer is one of the most commonly diagnosed diseases worldwide; its mortality rate is high, and there is still a demand for the development of antitumor active drugs. Triterpenoic acids show many pharmacological effects, among them antitumor activity. One of these, maslinic acid-1 is of interest because of its antitumor profile. It is not only cytotoxic but also triggers apoptosis in various human tumor cell lines. To improve the cytotoxicity of parent 1 we set out to synthesize a series of esters and amides differing in structure and lipophilicity. These compounds were tested in a sulforhodamine B assay for cytotoxicity, and screened for their ability to induce apoptosis using an acridine orange/propidium iodide assay, DNA laddering and cell cycle experiments. Esters containing small-chain, lipophilic residues increased the cytotoxicity whereas amides as well long-chain esters led to a decrease in activity. The antitumor activity seems to be independent from the substitution pattern at position C-28 for esters and amides but alters their mode of action.