Zephycandidine A, the First Naturally Occurring Imidazo[1,2-f]phenanthridine Alkaloid from Zephyranthes candida, Exhibits Significant Anti-tumor and Anti-acetylcholinesterase Activities

Zephycandidine A (1), the first naturally occurring imidazo[1,2-f]phenanthridine alkaloid, was isolated from Zephyranthes candida (Amaryllidaceae). The structure of 1 was elucidated by spectroscopic analyses and NMR calculation, and a plausible biogenetic pathway for zephycandidine A (1) was proposed. Zephycandidine A (1) exhibited significant cytotoxicity against five cancer cell lines with IC50 values ranging from 1.98 to 7.03 μM with selectivity indices as high as 10 when compared to the normal Beas-2B cell. Further studies suggested that zephycandidine A (1) induces apoptosis in leukemia cells by the activation of caspase-3, upregulation of Bax, downregulation of Bcl-2, and degradation of PARP expression. In addition, zephycandidine A (1) showed acetylcholinesterase (AChE) inhibitory activity, and the docking studies of zephycandidine A (1) and galanthamine (2) with AChE revealed that interactions with W286 and Y337 are necessary.