Alkaloids with cytotoxic activities from Zanthoxylum nitidum

Two previously undescribed alkaloids, 8-O-demethylmaclekarpine D (1) and zanthonitine (2), along with a pair of inseparable rotamers, 4-hydroxyl-beecheyamide (3a) and (E)-3-(4-hydroxy-3-methoxyphenyl)-N-(4-methoxyphenethyl)-N-methylacrylamide (3b), were isolated from Zanthoxylum nitidum. These compounds were accompanied by 35 known alkaloids, including benzophenanthridines (4-21), quinolines (22-31), aporphines (32-35) and other structural types (36-38). Structural elucidation was achieved through comprehensive spectroscopic analyses, including NMR, HRESIMS, X-ray crystallography, ECD and calculated ¹³C NMR DP4+ analysis. Cytotoxicity evaluation revealed compounds 6, 7, 18 and 33 (IC₅₀ = 7.29-22.90 μM) exhibited potent inhibitory effects on the proliferation of HepG2 cells, outperforming the efficacy of doxorubicin (IC₅₀ = 28.92 ± 0.48 μM). Similarly, compounds 9, 16 and 21 (IC₅₀ = 21.77-25.13 μM) suppressed SW480 cells, superior to doxorubicin (IC₅₀ = 31.15 ± 0.24 μM).