Structurally diverse flavonoids from Selaginella doederleinii and their biological activity against laryngeal cancer

Ten previously undescribed flavonoids, seladoeflavones J-Q, C, and E (1-10), together with fifteen known biflavones (11-25), were isolated from the whole herbs of Selaginella doederleinii. The structures of the new compounds were elucidated using 1D and 2D nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS). By comparing experimental spectral data with NMR calculations, the structures of compounds 1-5, 7, and 8 were assigned. The absolute stereochemistries of compounds 5-10 were confirmed by comparing their circular dichroism (CD) spectra with reported data. Notably, the originally proposed structures of seladoeflavones C and E were revised and found to be identical to those of compounds 7 and 8, respectively. All isolated compounds were evaluated for cytotoxic activity against a panel of cancer cell lines. Most notably, 2″,3″-dihydroochnaflavone (14) and involvenflavone G (19) exhibited significant anti-proliferative and pro-apoptotic effects in laryngeal cancer cells (Hep-2 and FaDu). Mechanistic studies revealed that compound 14 induced apoptosis by suppressing the protein kinase B (Akt)/mammalian target of rapamycin (mTOR) signaling pathway, whereas compound 19 downregulated endoplasmic reticulum (ER) stress pathways. These findings indicate that compounds 14 and 19 possess strong potential as anti-laryngeal cancer agents, providing robust evidence for the traditional use of S. doederleinii in the treatment of laryngeal cancer.