Lupeol fatty acid esters and an alkyl cycloartane ether from Cynanchum acutum with antimicrobial, antioxidant, and cytotoxic activities

Phytochemical investigation of the n-hexane extract of Cynanchum acutum afforded one known lupeol fatty acid ester (1), reported here for the first time from C. acutum, and two previously undescribed lupane/cycloartane-type triterpenoid derivatives, including a lupane-type unsaturated fatty acid ester (2) and a C7 alkyl ether cycloartane derivative (3), together with three known triterpenoids (4-6) and one known sterol (7). The structures of the isolated compounds were established by comprehensive analyses of 1D and 2D NMR, EI-MS, and HRESIMS data. Antimicrobial assays using the agar well diffusion and broth microdilution methods revealed marked antimicrobial activities against selected bacterial and fungal strains. Notably, the acetylated lupane derivative 4 exhibited potent antibacterial activity against Bacillus cereus (MIC = 3.2 ± 0.2 μM; MBC = 6.4 ± 0.4 μM), exceeding that of the reference antibiotic amoxicillin. Additionally, the previously undescribed unsaturated fatty acid ester 2 showed strong antifungal activity against Aspergillus niger (MIC = 1.9 ± 0.1 μM). DPPH radical-scavenging evaluation revealed that the norditerpene ketone 6 possessed the highest antioxidant activity (IC₅₀ = 151.7 ± 3.5 μM), supporting the importance of a free C-3 hydroxyl group in radical-scavenging activity. Cytotoxic evaluation against MCF-7 and WI-38 cell lines showed moderate antiproliferative effects, with compound 2 displaying the highest activity against MCF-7 cells (IC₅₀ = 76.8 ± 4.7 μM). Overall, this study expands the chemical diversity of C. acutum and provides further evidence for the biological activities associated with structurally diverse lupane- and cycloartane-type triterpenoids.