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In this study, four previously undescribed flavonoids, named epimesatines P (<b>1</b>), Q (<b>2</b>), R (<b>3</b>), and S (<b>4</b>), were isolated from the aerial parts of <i>Epimedium sagittatum</i> Maxim. Their structures and absolute configurations were confirmed via spectroscopic analyses, quantum chemical electronic circular dichroism (ECD) calculations, Mo₂(OAc)₄–induced ECD, and Rh₂(OCOCF₃)₄–induced ECD experiments. Epimesatines Q and R were characterized by the presence of furan rings. A cytotoxicity assay demonstrated that epimesatines P–S exhibited significant inhibitory effects on the viability of MCF-7 human breast cancer cells, with IC₅₀ values ranging from 1.27 to 50.3 μM. Notably, epimesatines Q and R exhibited superior efficacy against MCF-7 cells compared to epimesatines P and S, suggesting that the presence of furan rings may enhance their activity against MCF-7 cells. Specifically, epimesatine Q displayed a more potent inhibitory effect at 1.27 μM compared to a positive control, docetaxel, which had an IC₅₀ of 2.13 μM, highlighting its potential as a therapeutic agent for breast cancer. Importantly, none of the tested compounds exhibited obvious toxicity toward MCF-10A human breast epithelial cells. Furthermore, compounds <b>1</b>, <b>3</b>, and <b>4</b> were found to significantly inhibit the expression of sphingosine kinase 1 (Sphk1) in MCF-7 cells.