Phytochemical profiling of Bai traditional food: Eight previously undescribed meroterpenoids derivatives with cytotoxic potential from the flowers of Rhododendron pachypodum

Abstract

The flowers of Rhododendron pachypodum (Ericaceae), a traditional edible vegetable of the Bai ethnic group in Yunnan Province, China, are widely used both as food and medicine. A systematic phytochemical survey was conducted to fill the knowledge gap regarding its bioactive constituents. Fourteen meroterpenoids, including eight previously undescribed meroterpenoid compounds, rubiginosin I–J (1–2), (±)-rubiginosin K (3), (±)-rubiginosin L (4), (±)-rubiginosin N (5), and six known analogues (6–11), were structurally elucidated using a combination of spectroscopic techniques (1D/2D NMR, HRESIMS, UV, IR). The absolute configurations were unambiguously established by X-ray crystallography and ECD calculations. ‌Selected compounds were assessed for their cytotoxicity, α-glucosidase inhibition, and DPPH radical scavenging activities. Compound 6 demonstrated cytotoxic effects against‌ HepG2 and HeLa cell lines, with IC₅₀ values of 40.56 μM and 57.43 μM, respectively. Compound 7 exhibited a slight cytotoxic activity against A549 cell lines, with an inhibition rate of 60 %, while compound 8 demonstrated mild activity against both A549 and MDA-MB-468 cells, with inhibition rates of 70 % and 65 %, respectively, at a concentration of 100 μM. In the α-glucosidase inhibition assay, compounds 2–11 showed weak activity at 100 μg/mL. Similarly, in the DPPH assay, these compounds exhibited poor free radical scavenging activity at 100 μg/mL. This study not only expands the chemical diversity of meroterpenoids in Rhododendron pachypodum, but also provides the first evidence of their cytotoxic potential, although structural optimization is required to enhance bioactivity.