Two New Alkaloids and a Triterpenoid Glycoside from Rosa roxburghii with Antioxidant and Enzyme Inhibitory Activities

Rosa roxburghii is a distinctive medicinal and edible plant resource. In an effort to uncover structurally novel secondary metabolites from this plant and explore their pharmacological potential, a phytochemical investigation of the fresh fruits of R. roxburghii led to the isolation of two new dihydroavicine alkaloids, roxburghcids D (1) and E (2), and a new triterpenoid glycoside, roxburghcid C (6), together with five known compounds (3-5, 7-8). The structures of the new compounds were unambiguously elucidated through extensive spectroscopic analyses (including 1D and 2D NMR and HRESIMS), quantum chemical calculations, and single-crystal X-ray diffraction. In bioassay evaluations, compounds 2 and 3 exhibited significant ABTS radical scavenging activities, with IC₅₀ values of 39.59 and 17.38 μM, respectively. Additionally, compounds 2, 6, and 8 exhibited modest α-glucosidase inhibitory activities, with inhibition rates of 33.13%, 38.61%, and 36.85%, respectively, at a concentration of 100 μM. Furthermore, compounds 2 and 4 showed significant cytotoxicity against the A549 human cancer cell lines, with IC₅₀ values of 7.23 and 8.36 μM, respectively. This study represents the first report of alkaloids isolated from R. roxburghii, enriching its phytochemical profile and providing valuable chemotaxonomic insights for this species.